Category: Weekly Brief

CAWA Weekly Meteorology Brief — October 5, 2026

The week at a glance

Central Appalachia is heading into a quieter stretch of weather. A cold front will bring cooler air and a gusty breeze Monday, followed by the week’s main concern: frost Monday night into Tuesday morning.

The best chance of frost will be across northern Pennsylvania, the mountains of northern West Virginia and western Maryland. A few of the coldest ridgetops may approach freezing. Gardeners and anyone with temperature-sensitive plants should be ready to protect them Monday evening.

Tuesday through Saturday should be mostly dry. Temperatures gradually recover later in the week. Rain may return Sunday, but the timing and coverage are still uncertain.

The practical takeaway: prepare for frost Monday night, then expect several low-impact fall days.

Full technical briefing

Seven-day forecast for Central Appalachia

This outlook covers western Pennsylvania, eastern Ohio, northern West Virginia, western Maryland and nearby portions of Central Appalachia.

Day	Expected pattern	Main concern	What CAWA should do
Monday, Oct. 5	Cold front followed by clearing	Gusty wind; frost developing at night	Prepare frost messaging for northern and mountain counties
Tuesday, Oct. 6	Cold morning, sunny afternoon	Morning frost; isolated freezing temperatures on ridgetops	Check observations and any official frost or freeze headlines early
Wednesday, Oct. 7	Dry and warmer	Breezy in parts of eastern Ohio; localized early mountain frost	Routine monitoring is enough
Thursday, Oct. 8	Mostly sunny and seasonable	No significant hazard expected	Use normal forecast coverage
Friday, Oct. 9	Weak front nearby	Little or no rain expected	Watch for small timing changes, but no active coverage is indicated
Saturday, Oct. 10	Dry and mild	No significant hazard expected	Routine monitoring is enough
Sunday, Oct. 11	Clouds increasing; rain possible	Timing and coverage of returning rain remain uncertain	Monitor the Gulf system before making a firm rainfall forecast

Monday: Cooler air arrives

A cold front will cross the region, but it should have little moisture to work with. Most places will stay dry. Clouds should decrease through the day as cooler air spreads southeast.

Northwest winds may gust between 20 and 25 mph, especially across western Maryland and the higher terrain. This is below typical advisory criteria, but it may be noticeable during outdoor activities.

Attention then turns to Monday night. Canadian high pressure settling over the region will allow temperatures to fall into the middle and upper 30s across many northern and elevated locations. The Allegheny ridges could approach freezing.

The most likely frost areas include northwestern Pennsylvania, Forest and Jefferson counties in Pennsylvania, Preston and Tucker counties in West Virginia, and the colder valleys and ridges of western Maryland. Confidence is moderate: temperatures support frost, but lingering clouds or a slight breeze could limit how widespread it becomes.

Prepare a simple frost graphic Monday afternoon. Clearly identify any Frost Advisory or Freeze Warning as an official NWS product if one is issued.

Sources: NWS Pittsburgh forecast discussion, NWS Baltimore/Washington forecast discussion forecast.weather.gov

Tuesday: Frosty start, quiet afternoon

Tuesday morning should be the coldest part of the week. Frost may be widespread west of the Blue Ridge and more localized around Pittsburgh and eastern Ohio. Temperatures on the highest Allegheny ridgetops could briefly reach freezing.

Patchy valley fog is also possible in West Virginia, with locally dense fog in protected mountain valleys. It should lift during the morning.

Sunshine will follow, but afternoon temperatures will remain cool—generally in the 60s, with 50s in some mountain communities.

Check temperatures, visibility and official NWS headlines early Tuesday. Once fog and frost clear, routine coverage should be sufficient.

Sources: NWS Charleston forecast discussion, NWS Baltimore/Washington forecast discussion forecast.weather.gov

Wednesday: Warmer, with a breeze in the west

Southerly flow will begin returning warmer air to the region. Most areas should remain sunny and dry.

A few sheltered locations in the northern West Virginia mountains could see another touch of frost early Wednesday, but the threat should be less extensive than Tuesday morning. Farther west, southwest winds may gust around 20 to 25 mph during the afternoon in portions of eastern Ohio.

Neither concern currently appears significant enough for broad public messaging. Routine monitoring is enough unless local observations become more impactful.

Source: NWS Cleveland forecast discussion forecast.weather.gov

Thursday through Saturday: A quiet fall stretch

High pressure should keep most of Central Appalachia dry through Saturday. Temperatures will gradually recover, with pleasant afternoons and cool nights.

A weak cold front may pass late in the week, but current guidance suggests it will have little moisture. No organized severe-weather, flooding or excessive-heat signal is apparent in the local NWS guidance.

Use normal forecast coverage. This should be a good period for reviewing tools and preparing for the upcoming operational model transition.

Sources: NWS Pittsburgh forecast discussion, NWS Cleveland forecast discussion forecast.weather.gov

Sunday: Rain may return

Forecast guidance suggests moisture could move north from the Gulf late in the weekend. That would bring increasing clouds and a chance of rain, particularly across West Virginia and western Maryland.

Confidence is low on the system’s track, timing and rainfall totals. The possibility is worth watching, but it is too early to advertise heavy rain or flooding.

Monitor later model runs and any National Hurricane Center outlooks during the week. Hold off on specific rainfall graphics until the track becomes clearer.

Sources: NWS Pittsburgh forecast discussion, NWS Charleston forecast discussion forecast.weather.gov

Operational meteorology and communication updates

RRFS and REFS implementation is now scheduled for October 14

Updated scheduled implementation

An important correction to earlier CAWA briefings: NCEP’s latest service notice schedules the operational implementation of RRFS and REFS for October 14, 2026—not October 6.

The retirement of NAM, SREF, HREF, HiresW and NAM MOS has also moved to October 14. Parallel RRFS and REFS data remain available for testing.

The extra eight days provide more time to check CAWA scripts, bookmarks, dashboards and graphics. Any workflow that directly requests a retiring model could fail after the transition. Particular attention should go to HREF severe-weather probabilities, NAM soundings, SREF plumes and NAM MOS displays.

Before October 14:

Search code and configuration files for nam, namnest, sref, href, hiresw and NAM MOS products.
Confirm that replacement RRFS or REFS fields use the expected units and accumulation periods.
Test missing-data and stale-data alarms.
Avoid assuming that similarly named RRFS and HRRR fields are directly interchangeable.

Sources: Updated RRFS and REFS implementation notice, updated model-retirement notice weather.gov

WPC’s Probabilistic Precipitation Portal is operational

Implemented around October 1

The Weather Prediction Center’s Probabilistic Precipitation Portal has moved from experimental to operational status.

The portal can help answer questions that a single deterministic rainfall map cannot, such as the probability of exceeding a certain amount at a location. That should be useful when CAWA is evaluating marginal heavy-rain situations or explaining why confidence in a specific rainfall total is limited.

If portal graphics are used publicly, always retain the threshold, probability and valid period. A map showing a “40% chance” is incomplete without explaining what rainfall amount has a 40% chance of being exceeded.

Sources: NWS service-change notices, WPC Probabilistic Precipitation Portal weather.gov

“Particularly Dangerous Situation” wording expands to two winter warnings

Implemented around October 1

The NWS can now include Particularly Dangerous Situation wording in exceptionally serious Blizzard Warnings and Ice Storm Warnings.

PDS is not a separate warning. It is stronger wording within an existing official warning, reserved for unusually dangerous situations with potentially extreme impacts.

CAWA’s alert automation should preserve the PDS language instead of dropping it during summarization. Public posts should immediately explain the expected impact—such as prolonged whiteout conditions, crippling ice accumulation or extended power failures—rather than assuming everyone understands the label.

Source: NWS service-change notices weather.gov

Graphical Hazardous Weather Outlook begins operational transition October 15

Scheduled change

The experimental Graphical Hazardous Weather Outlook is scheduled to begin transitioning to operational status October 15, with completion expected by October 30.

These outlooks can support quick briefings by presenting potential hazards graphically, but they are still outlook information—not watches or warnings. CAWA should verify any links or automated retrieval routines that depend on an experimental label or endpoint.

When using GHWO graphics publicly, pair them with a plain-language explanation of timing and confidence. Avoid presenting a shaded outlook area as proof that hazardous weather will occur at every location inside it.

Source: NWS Graphical Hazardous Weather Outlook notice

This briefing is planning guidance, not an official warning or substitute for current forecasts. Follow watches, warnings and advisories issued by the National Weather Service. This post was created with AI assistance.

October 5, 2026

CAWA Weekly Meteorology Brief — September 27, 2026

The week at a glance

This should be a fairly quiet week across Central Appalachia.

Clouds left behind by the departing coastal storm may linger Monday, particularly across western Pennsylvania and the mountains. Patchy valley fog is also possible during the first few mornings of the week.

Tuesday through Thursday should be dry and increasingly warm. Thursday looks like the warmest day, with highs near 80 around Pittsburgh and well into the 80s in parts of West Virginia and western Maryland. Humidity will remain low enough to prevent a significant heat hazard.

A front may bring scattered showers beginning Thursday night or Friday. Rain chances could linger into the weekend, but forecast confidence drops considerably after Thursday. At this point, neither severe weather nor heavy rainfall appears likely.

Full technical briefing

Seven-day forecast for Central Appalachia

This outlook covers western Pennsylvania, eastern Ohio, northern West Virginia, western Maryland and nearby portions of Central Appalachia.

Day	Expected pattern	Main concern	What CAWA should do
Monday, Sept. 28	Mostly dry with lingering clouds	Early fog and low ceilings; isolated ridge drizzle	Check valley visibility before the morning update
Tuesday, Sept. 29	Dry and seasonable	Patchy morning valley fog	Routine monitoring is enough
Wednesday, Sept. 30	Sunny and warmer	No significant hazard expected	Routine monitoring is enough
Thursday, Oct. 1	Warmest day of the week	Unseasonable warmth; showers possible late	Watch the front’s timing Thursday evening
Friday, Oct. 2	Scattered showers possible	Wet roads; low-confidence storm chance	Keep coverage flexible rather than planning a full operation
Saturday, Oct. 3	Front may remain nearby	Scattered showers; cooler temperatures	Check whether rain is clearing from northwest to southeast
Sunday, Oct. 4	Uncertain frontal position	Additional showers possible	Reassess after the late-week system becomes better sampled

Monday: Clouds and pockets of fog

The coastal storm responsible for the weekend’s clouds and wind will continue pulling away. Most of the region should remain dry, although a little drizzle or an upslope shower could linger along the Laurel Highlands and the higher terrain of northern West Virginia and western Maryland.

Low clouds may be stubborn around western Pennsylvania. NWS Pittsburgh indicates a 40–60% chance that IFR ceilings linger into Monday morning at several aviation locations. Patchy valley fog is also possible, especially where skies clear and winds become light.

No land-based watches, warnings or advisories were in effect for the Pittsburgh, Cleveland or Charleston forecast areas Sunday afternoon.

Check webcams and visibility observations in the river valleys before posting the morning forecast. Conditions should gradually improve during the day. NWS Pittsburgh forecast discussion forecast.weather.gov

Tuesday: Quiet and seasonable

High pressure takes control Tuesday. Afternoon temperatures should generally reach the lower and middle 70s across eastern Ohio and western Pennsylvania, with somewhat warmer readings farther south.

Fog may redevelop before sunrise in the sheltered valleys of West Virginia and western Pennsylvania. NWS Charleston expects any dense valley fog to lift quickly after sunrise.

Routine monitoring is enough once the morning fog clears. NWS Charleston forecast discussion forecast.weather.gov

Wednesday: Warmer, with plenty of dry weather

Upper-level ridging will build across the eastern United States, allowing temperatures to climb. Most lower elevations should reach the middle or upper 70s, with lower 80s possible in parts of West Virginia.

Dry air and weak forcing should prevent meaningful shower development. No organized hazardous weather is evident.

Routine monitoring is enough. If fog forms early, it should be confined mainly to the usual sheltered valleys.

Sources: NWS Cleveland forecast discussion, NWS Baltimore/Washington forecast discussion forecast.weather.gov

Thursday: Warmest day of the week

Thursday should be the warmest day across most of the coverage area. NWS Pittsburgh places the probability of reaching at least 80 degrees between 50% and 80% across most lower elevations south of Interstate 80. Western Maryland may reach the middle 80s, while parts of the West Virginia lowlands could also climb well into the 80s.

This is unseasonably warm, but it does not currently qualify as a meaningful heat hazard. Dew points are expected to remain near or below the lower 60s, and NWS Pittsburgh places the chance of moderate-or-greater heat impacts at 10% or less.

A front approaching from the west may bring showers into eastern Ohio late Thursday or Thursday night. Timing remains uncertain, with recent guidance trending slower.

Watch the front’s progress Thursday evening. There is no reason yet to prepare heat alerts or active storm coverage. NWS Pittsburgh forecast discussion forecast.weather.gov

Friday: Scattered showers, but limited hazards

The front should bring scattered showers into more of the region Friday. Rainfall is expected to remain modest: NWS Pittsburgh places the chance of exceeding half an inch during any 24-hour period below 40%.

Severe-weather potential also appears muted because instability should be weak. A rumble of thunder cannot be ruled out, but current official local guidance does not identify an organized damaging-wind, hail or tornado threat.

Confidence is moderate that some rain occurs, but low on its exact timing and coverage. Keep coverage flexible and avoid presenting Friday as a washout this far in advance.

Saturday and Sunday: Forecast confidence drops

The weekend depends on how quickly the front moves through the Appalachians. Scattered showers may linger, especially over West Virginia and western Maryland, while eastern Ohio and western Pennsylvania could begin drying sooner.

NWS Charleston notes substantial model-to-model and run-to-run differences after Thursday. NWS Baltimore/Washington likewise says temperatures and rain chances hinge on how far south the front advances.

No official severe-weather or excessive-rainfall signal is identified at this range. Check Saturday morning whether conditions are clearing from northwest to southeast, then reassess Sunday rather than carrying an outdated broad rain message through the entire weekend. forecast.weather.gov

Operational meteorology and communication updates

WPC’s Probabilistic Precipitation Portal becomes operational this week

Status: Operational transition scheduled around October 1

WPC’s Probabilistic Precipitation Portal is scheduled to transition from experimental to operational status around October 1. The portal displays the probability of exceeding selectable precipitation amounts during the next 72 hours, along with ranges of plausible totals.

For CAWA, its best use is helping explain uncertainty when deterministic rainfall maps disagree or when narrow heavy-rain corridors are possible. It may be especially useful for deciding whether public messaging should emphasize a likely general rainfall or a lower-probability, higher-impact outcome.

If CAWA uses its graphics publicly, always include:

The rainfall threshold being shown
The probability of exceeding that threshold
The valid period
A reminder that the probability is not a predicted coverage percentage

Bookmark and begin testing the NWS Probabilistic Precipitation Portal. wpc.ncep.noaa.gov

RRFS and REFS implementation is one week away

Status: Scheduled implementation October 6

NCEP remains scheduled to implement RRFS and REFS on October 6. Operational production of NAM, NAM Nest, SREF, HREF, HiresW and NAM MOS is expected to end with that transition.

This is now an immediate data-continuity issue. Any CAWA dashboard, spreadsheet, downloader or forecasting workflow using the retiring datasets should have a tested replacement before next week’s briefing.

The field names and statistical construction of REFS products are not necessarily identical to similarly named HREF fields. Avoid swapping URLs while assuming the resulting probabilities mean exactly the same thing.

Source: NWS RRFS and REFS implementation notice

CAP comment period has closed

Status: Proposal remains under consideration

The initial NWS comment period concerning a possible transition from VTEC-centered alert dissemination to Common Alerting Protocol messages closed September 21.

No final implementation decision or transition schedule is identified at this time. CAWA should continue supporting its current alert workflow while documenting any dependence on raw VTEC strings.

Do not remove VTEC processing based solely on the proposal. Wait for a formal NWS decision, technical documentation and implementation schedule.

Source: NWS CAP transition information weather.gov

No other consequential national change identified

No additional NWS, SPC, WPC, NCEP, MRMS or AWIPS change with a clear operational impact on CAWA was identified since the previous briefing.

The primary work items remain the October 1 precipitation-portal transition and the much larger October 6 RRFS/REFS implementation and legacy-model retirement.

September 27, 2026

CAWA Weekly Meteorology Brief — September 20, 2026

The week at a glance

Keep the rain gear handy. Several weather systems will cross Central Appalachia through the middle of the week, bringing repeated rain and a few thunderstorms.

The greatest immediate concern is flooding Monday. Official Flood Watches cover much of southeastern Ohio, northern and central West Virginia, southwestern Pennsylvania and areas near and south of Pittsburgh. Another half-inch to inch and a half of rain is possible in parts of the region, with narrow corridors potentially receiving more.

Rain becomes lighter and less organized after Monday, but additional showers through Wednesday could keep streams elevated and cause slower river rises. Temperatures will also turn sharply cooler. Many communities from eastern Ohio through western Pennsylvania may remain in the 60s for several days.

Drier weather should return late Thursday or Friday. The weekend currently looks cool, pleasant and much quieter.

Full technical briefing

Seven-day forecast for Central Appalachia

This outlook covers western Pennsylvania, eastern Ohio, northern West Virginia, western Maryland and nearby portions of Central Appalachia.

Day	Expected pattern	Main concern	What CAWA should do
Monday, Sept. 21	Periods of rain with embedded storms	Flash flooding, standing water and isolated strong wind	Plan for active flood coverage through the morning
Tuesday, Sept. 22	Cool, cloudy and damp	Additional rain; elevated streams and rivers	Continue checking rainfall totals and water levels
Wednesday, Sept. 23	More widespread showers	Longer-duration flooding; poor visibility	Keep flood messaging available even if rain is lighter
Thursday, Sept. 24	Lingering showers, gradually improving	Gusty wind east; isolated remaining water issues	Confirm the upper low and coastal system are moving away
Friday, Sept. 25	Drier with partial clearing	Chilly morning temperatures	Routine monitoring should be enough
Saturday, Sept. 26	Dry and seasonably cool	No significant hazard expected	Routine monitoring is enough
Sunday, Sept. 27	Mainly dry with increasing clouds possible	No organized hazard identified	Watch for changes in the next approaching system

Monday: Flooding is the main concern

Official NWS Flood Watches extend through Monday morning across much of southeastern Ohio, northern and central West Virginia, southwestern Pennsylvania and counties near and south of Pittsburgh.

A moisture-rich system will produce another round of rain overnight into Monday morning. NWS Pittsburgh expects a general half-inch to inch and a half near and south of the city, but high-resolution guidance shows the possibility of narrow two- to three-inch corridors. The exact placement will depend on where the slow-moving front settles.

The ground is already wet in many locations. That raises the risk of flash flooding along small streams, in low spots and in poor-drainage areas. NWS Charleston notes that places hit by heavy rain Sunday will be particularly vulnerable.

A few thunderstorms may produce strong wind, especially across southeastern Ohio and West Virginia. Widespread severe weather is not the primary concern; extensive clouds and limited instability should keep that threat isolated.

Confidence is high that more rain occurs and moderate on the flash-flood threat. Confidence is lower on exactly where the heaviest stripe sets up.

Plan for active flood coverage through Monday morning. Track observed rainfall, road closures and stream responses instead of relying on the regional forecast alone.

Sources: NWS Pittsburgh forecast discussion, NWS Charleston forecast discussion

Tuesday: Cooler, with lingering rain

Canadian high pressure pressing south will bring much cooler air into eastern Ohio and western Pennsylvania. Highs there may struggle to leave the lower or middle 60s. West Virginia will remain somewhat warmer, particularly south of the stalled boundary.

Clouds, scattered showers and low ceilings will continue. Rainfall rates should generally be lower than Monday, reducing the immediate flash-flood threat. Even so, runoff from several days of rain may keep streams elevated.

Western Maryland could receive steadier rain Monday night into early Tuesday as moist easterly flow strengthens against the terrain.

Continue checking rainfall totals, river forecasts and any extensions of the Flood Watch. Public messaging should separate ongoing river or stream responses from the lower risk of new, rapid flash flooding.

Sources: NWS Cleveland forecast discussion, NWS Baltimore/Washington forecast discussion

Wednesday: Another round of showers

An upper-level trough will move into the Ohio Valley, bringing another period of widespread showers. Thunder is possible, but cool temperatures and limited instability should keep severe-weather potential low.

NWS Pittsburgh notes that longer-duration rainfall may produce river rises or overflow flooding through Wednesday, even as the risk of intense short-term rainfall decreases. Areas along and south of the Pennsylvania–West Virginia border deserve particular attention.

It will feel distinctly autumnal. Lower elevations in western Pennsylvania and eastern Ohio should remain in the lower or middle 60s, while some higher ridges may struggle to reach 60.

Keep flood messaging available Wednesday. If water problems develop, emphasize that flooding can continue after the heaviest rain ends.

Thursday: Slow improvement

The upper trough may close off before finally moving east. Scattered showers could linger, particularly over West Virginia, the higher terrain and western Maryland.

A coastal low moving north near the Mid-Atlantic coast may also produce gusty northerly or northeasterly winds in western Maryland. The stronger wind and coastal-flood threat should remain east of CAWA’s primary coverage area, but gusts may become noticeable along exposed ridges.

Confidence in gradual improvement is moderate; the main uncertainty is how quickly the upper and coastal lows depart.

Confirm that the systems are pulling away before dropping rain and wind coverage. Otherwise, routine monitoring should become sufficient later in the day.

Source: NWS Baltimore/Washington forecast discussion

Friday: Drying out

High pressure should begin taking control, bringing clearing skies and a welcome break from the rain.

Morning temperatures may fall into the 40s across inland northeastern Ohio, northwestern Pennsylvania and the higher terrain. Widespread frost or freezing conditions are not currently expected.

Routine monitoring should be enough. Check sheltered valleys for lower temperatures if skies clear more quickly than forecast.

Saturday and Sunday: A quieter fall weekend

The weekend currently looks dry and seasonably cool. Afternoon temperatures should generally reach the upper 60s or lower 70s, with chilly nights in the 40s and lower 50s.

Forecast confidence is moderate to high for Saturday and somewhat lower by Sunday. No organized hazardous-weather signal is evident at this range.

Routine monitoring is enough, with a check Sunday for the timing of the next system beyond the seven-day period.

Additional operational concerns

Lake Erie remains hazardous early in the week

NWS Cleveland has issued Beach Hazards Statements for portions of the Ohio and Pennsylvania Lake Erie shoreline through Wednesday evening. Small Craft Advisories are also in effect.

Persistent northeast winds may gust around 30 mph in northwestern Ohio, with higher waves and dangerous currents along the lakeshore. These are official NWS hazards and are separate from the inland flood threat.

If CAWA’s coverage includes Erie County or the northeastern Ohio lakeshore, keep the beach and marine message visible through Wednesday.

Source: NWS Cleveland forecast discussion and active headlines

Operational meteorology and communication updates

No major new national product change was identified this week

No consequential new NWS, SPC, WPC, NCEP, MRMS or AWIPS change relevant to CAWA operations was identified since the previous briefing. Several previously announced deadlines still require attention.

CAP transition comments close September 21

Status: Proposal under review

The NWS comment period on potentially making Common Alerting Protocol messages its primary alert format closes Monday.

This remains an early proposal, not an implementation notice. A future transition could affect any CAWA automation that depends on raw VTEC strings to identify warning actions, event numbers, extensions or cancellations.

If CAWA has concerns about migration time, alert tracking or access to legacy text products, Monday is the last scheduled day to provide initial feedback.

Source: NWS CAP transition proposal

Verify the completed NEXRAD Level II migration

Status: Scheduled change date has passed

NWS scheduled the old NOMADS directory for NEXRAD Level II data to be discontinued September 15. Identical files are available through TGFTP, and Level III products were not affected.

Any CAWA tool using Level II data should now be checked for both connectivity and freshness. A successful request is not enough; confirm that file timestamps continue advancing and that all expected radar sites are present.

Source: NEXRAD Level II migration notice

WPC precipitation portal approaches operational status

Status: Operational transition planned around October 1

WPC’s Probabilistic Precipitation Portal is scheduled to move from experimental to operational status around October 1.

This week’s repeated-rain setup is a good example of where probabilistic information can add value. A single rainfall-total map may obscure uncertainty in the location of a narrow heavy-rain corridor. Threshold probabilities can better show how likely a location is to receive one, two or three inches.

When sharing probabilistic rainfall information publicly, always include the accumulation threshold, valid period and geographic context.

Source: NWS service-change notices

RRFS/REFS transition is about two weeks away

Status: Implementation scheduled for October 6

RRFS and REFS remain scheduled to become operational October 6. NAM, SREF, HREF, HiresW and NAM MOS production is expected to end with the transition.

CAWA should be beyond the inventory stage by now. Any dashboard, automated download, bookmark or forecast process using the retiring systems should have a tested replacement or a documented plan for temporary loss of that component.

Source: RRFS and REFS implementation notice

September 20, 2026

CAWA Weekly Meteorology Brief — September 13, 2026

The week at a glance

Monday will feel noticeably cooler and less humid across Central Appalachia. That break will not last long: temperatures and humidity climb Tuesday, with hot conditions returning to West Virginia by Wednesday.

Thunderstorms may begin near Lake Erie and northeastern Ohio Tuesday night. Scattered storms remain possible Wednesday and Thursday as a front wavers across the region. Another front may bring additional showers and storms from Thursday into the weekend.

The forecast supports keeping an eye on storms, but it does not yet point to a widespread or high-confidence severe-weather event. The more certain concern is heat across the West Virginia lowlands Wednesday and Thursday, where heat-index values may approach 100 degrees.

Full technical briefing

Seven-day forecast for Central Appalachia

This outlook covers western Pennsylvania, eastern Ohio, northern West Virginia, western Maryland and nearby portions of Central Appalachia.

Day	Expected pattern	Main concern	What CAWA should do
Monday, Sept. 14	Cooler and less humid	Breezy conditions; early clouds or fog south	Routine monitoring is enough
Tuesday, Sept. 15	Dry and quickly warmer	Storms may approach northeastern Ohio at night	Watch northern Ohio Tuesday evening
Wednesday, Sept. 16	Hot and humid; scattered storms	Heat in West Virginia; isolated strong storms	Publish heat reminders and monitor afternoon storms
Thursday, Sept. 17	Humid with on-and-off storms	Heat, gusty storms and locally heavy rain	Keep coverage plans flexible
Friday, Sept. 18	Front crossing or nearby	Scattered showers and storms	Follow the front before scaling back
Saturday, Sept. 19	Front may linger south and east	Additional showers or storms	Focus monitoring on West Virginia and western Maryland
Sunday, Sept. 20	Unsettled in some guidance	Scattered storms; timing uncertain	Check updated guidance before weekend messaging

Monday: Cooler air settles in

A cold front departing early Monday will leave behind a cooler, drier air mass. Highs should range from near 70 in northeastern Ohio and northwestern Pennsylvania to the middle and upper 70s farther south. Mountain locations will be cooler.

Northwest winds may gust between 20 and 25 mph in western Maryland and the higher terrain. That falls short of a significant land-based wind hazard, but it will make the day feel more autumnal. Low clouds or fog could briefly affect parts of West Virginia early in the morning.

NWS Cleveland has issued Beach Hazards Statements along portions of Lake Erie through Monday morning, along with Small Craft Advisories for the lake. These are official NWS alerts, primarily affecting marine and lakeshore interests.

Routine monitoring is enough away from Lake Erie. Mention the lakeshore hazard if CAWA’s morning coverage reaches northwestern Pennsylvania or northeastern Ohio.

Sources: NWS Cleveland forecast discussion, NWS Baltimore/Washington forecast discussion

Tuesday: Temperatures rebound

High pressure shifts east and return flow develops, allowing temperatures to climb quickly. Many lower elevations should return to the lower and middle 80s. The West Virginia lowlands may become hotter, although humidity should remain below its midweek peak.

A warm front near Lake Erie may produce showers or thunderstorms Tuesday night across northern Ohio. Confidence decreases farther south, where most of the day should remain dry.

Watch northeastern Ohio Tuesday evening. Broader active-weather coverage probably will not be necessary unless storms become more organized than currently expected.

Sources: NWS Cleveland forecast discussion, NWS Pittsburgh forecast discussion

Wednesday: Heat south, scattered storms possible

Wednesday brings summer back to the region. Temperatures should reach the middle and upper 80s across much of western Pennsylvania, eastern Ohio and western Maryland. Lower elevations in West Virginia may reach the lower 90s.

NWS Charleston expects heat-index values in the middle and upper 90s across much of the lowlands, with readings approaching 100 in urban parts of the Kanawha Valley. That is the clearest impact signal in the current forecast. This is not a statement that a Heat Advisory has been issued.

A nearly stationary boundary could also support scattered thunderstorms. NWS Pittsburgh notes early guidance suggesting a low-end severe and flooding signal Wednesday and Thursday, but that signal remains uncertain. NWS Cleveland has not yet identified a focused severe threat and plans to reevaluate the convective environment as the event gets closer.

Publish a straightforward heat reminder for West Virginia. Monitor afternoon storm development, but wait for stronger support from SPC or later local NWS forecasts before advertising an organized severe threat.

Sources: NWS Charleston forecast discussion, NWS Pittsburgh forecast discussion

Thursday: Humid with several possible hazards

A front may remain near northeastern Ohio and western Pennsylvania while another disturbance approaches. Scattered or periodically more numerous thunderstorms are possible.

The main concerns are locally gusty wind, downpours and lightning. Repeated storms could create isolated drainage or poor-drainage flooding, but the available guidance does not support presenting a widespread flash-flood event as likely.

Hot weather may continue in the West Virginia lowlands, where afternoon heat indices could again reach the middle or upper 90s. Farther north, clouds and storms may hold temperatures down.

Confidence is moderate that some part of the region receives storms, but lower on their timing, coverage and strength. Keep coverage plans flexible and review the newest SPC convective outlook and WPC excessive-rainfall outlook before drawing a specific risk area.

Friday: Frontal timing becomes important

Forecast guidance generally brings a cold front through part of the region late in the week. Showers and thunderstorms may accompany it, particularly from western Pennsylvania southward into West Virginia and western Maryland.

Severe probabilities currently appear limited in the eastern coverage area. The front’s timing is still unsettled, and an earlier passage would reduce both instability and storm intensity.

Follow the front rather than committing to a full-day storm message. If it clears early, much of eastern Ohio and western Pennsylvania may turn cooler and quieter.

Source: NWS Baltimore/Washington forecast discussion

Saturday and Sunday: Lower-confidence storm chances

The weekend forecast depends on how quickly the late-week front clears the Appalachians. Western Pennsylvania and eastern Ohio have the better chance of turning cooler and drier first. Showers and thunderstorms could linger or redevelop across West Virginia and western Maryland.

NWS Charleston also notes that passing upper-level disturbances may provide daily opportunities for storms as the ridge weakens. At this range, neither day stands out as a defined severe-weather day.

Focus Saturday monitoring on the southern and eastern coverage area. Reassess Sunday after the front’s position becomes clearer.

Operational meteorology and communication updates

NEXRAD Level II data moves off NOMADS Monday

Scheduled change — September 15, 2026

NWS plans to discontinue the existing NEXRAD Level II directory on the NOMADS server at 1200 UTC Monday. Identical data are already available from the replacement TGFTP directory. Level III data are not included in this change.

Any CAWA script that still retrieves Level II files from:

https://nomads.ncep.noaa.gov/pub/data/nccf/radar/nexrad_level2

should be moved to:

https://tgftp.nws.noaa.gov/data/radar/nexrad_level2

The file format, frequency, filenames and directory structure are unchanged. After migrating, verify timestamps rather than merely confirming that the downloader runs successfully.

Source: NWS NEXRAD Level II migration notice

WPC’s Probabilistic Precipitation Portal is going operational

Scheduled implementation — on or about October 1, 2026

NWS Service Change Notice 26-75 says WPC’s experimental Probabilistic Precipitation Portal will transition to operational status around October 1.

The portal presents precipitation probabilities in a form that can help answer questions that a single deterministic QPF map cannot—for example, the chance of exceeding a particular rainfall amount at a location. That can be useful when CAWA needs to explain uncertainty around localized heavy-rain or flooding setups.

CAWA should evaluate the portal as an internal briefing and forecast-confidence tool. If its graphics are eventually used publicly, include the threshold and valid period prominently; a probability without those details is easy to misread.

Source: NWS service-change notices and announcements

CAP transition feedback remains open

Proposal — comments due September 21, 2026

NWS is gathering early feedback on making Common Alerting Protocol messages its primary watch, warning and advisory format, potentially ending traditional VTEC-formatted dissemination later.

This remains a proposal, with no implementation date. It still deserves attention because CAWA’s alert poster and other automated tools must correctly follow warning updates, cancellations and event identifiers.

Document every place where CAWA relies directly on VTEC strings. If the alert poster primarily consumes the NWS API, confirm which structured fields it uses and whether any event-tracking logic still parses raw product text.

Source: NWS CAP transition proposal

RRFS and REFS appear in local forecast operations

NWS Pittsburgh’s September 13 forecast discussion directly compared HREF and parallel REFS guidance while assessing the day’s severe-weather environment. That is a useful real-world sign that forecasters are already evaluating REFS alongside established convection-allowing guidance ahead of the planned October 6 operational transition.

CAWA can do the same during this week’s less-certain storm periods: compare REFS probabilities with HREF, observed instability and actual radar evolution. Keep the comparisons internal until there is enough experience to understand each field’s strengths and biases.

RRFS and REFS are still scheduled to become operational October 6, when NAM, SREF, HREF, HiresW and NAM MOS production is expected to end.

Sources: NWS Pittsburgh forecast discussion, RRFS and REFS implementation notice

September 13, 2026

CAWA Weekly Meteorology Brief – September 6, 2026

The week at a glance

Most of Central Appalachia gets a pleasant Labor Day before heat and humidity return. Wednesday will be the hottest day, with afternoon temperatures reaching the upper 80s and lower 90s in many valleys and lower elevations.

A cold front will bring thunderstorms into eastern Ohio and western Pennsylvania Wednesday evening or night. Storms should spread through northern West Virginia and western Maryland by Thursday. A few could produce damaging wind, but the forecast still depends heavily on when the front arrives and how many storms develop.

Cooler, less humid weather should follow Friday. Temperatures begin climbing again over the weekend.

The practical takeaway: enjoy Monday and Tuesday, use some heat caution Wednesday, and keep an eye on the forecast before Wednesday evening and Thursday plans.

Full technical briefing

Seven-day forecast for Central Appalachia

This outlook covers western Pennsylvania, eastern Ohio, northern West Virginia, western Maryland and nearby portions of Central Appalachia.

Day	Expected pattern	Main concern	What CAWA should do
Monday, Sept. 7	Dry and comfortable	Patchy early valley fog	Routine monitoring is enough
Tuesday, Sept. 8	Sunny, warmer	No organized hazard expected	Watch the developing heat trend
Wednesday, Sept. 9	Hot and increasingly humid	Heat; storms arriving northwest late	Update heat messaging and monitor storms approaching Ohio
Thursday, Sept. 10	Cold front with showers and storms	Isolated damaging wind; locally heavy rain	Be ready for active coverage if storms organize
Friday, Sept. 11	Front departing	Lingering early showers, mainly southeast	Check southern and eastern counties before scaling back
Saturday, Sept. 12	Dry and warmer	No significant hazard expected	Routine monitoring is enough
Sunday, Sept. 13	Warm with increasing humidity	Heat trend; forecast confidence lower	Watch whether the next warmup becomes more impactful

Monday: A quiet Labor Day

High pressure will keep Monday dry, with afternoon temperatures generally in the upper 70s and lower 80s. Humidity remains manageable.

Patchy river-valley fog may briefly reduce visibility around sunrise, especially in sheltered portions of West Virginia and western Pennsylvania. It should dissipate quickly. No weather alerts were in effect for the Pittsburgh, Cleveland or Charleston forecast areas Sunday afternoon.

Routine monitoring is enough. If CAWA publishes a morning forecast, mention fog only where it is actually observed.

Sources: NWS Pittsburgh forecast discussion, NWS Charleston forecast discussion

Tuesday: Warmer, but still quiet

Southerly flow develops as high pressure moves east. Afternoon temperatures should reach the lower and middle 80s, with a few warmer readings in the valleys. Humidity will begin creeping upward, but dangerous heat is not currently expected.

Use Tuesday to prepare Wednesday heat graphics and review staffing for the midweek frontal passage.

Source: NWS Cleveland forecast discussion

Wednesday: The hottest day, then storms approach

Wednesday should bring the week’s highest temperatures. Most lower elevations will reach the upper 80s or lower 90s. NWS Cleveland expects heat indices in the lower to middle 90s, while NWS Charleston forecasts lower 90s in parts of the Ohio–West Virginia–Kentucky Tri-State area.

This is a meaningful heat day, although current forecasts do not suggest a widespread high-end heat episode. People working or practicing outdoors should still take breaks and drink water.

A cold front will approach during the evening. NWS Cleveland expects moderate to strong instability ahead of it and says organized thunderstorms may develop across northern Ohio Wednesday evening or night. Damaging wind would be the main concern if a substantial line or cluster forms.

Confidence is moderate that thunderstorms reach eastern Ohio and northwestern Pennsylvania, but lower on their coverage and arrival time. This is an official local NWS forecast signal—not a claim by CAWA that a categorical SPC risk covers the region.

Update heat messaging Wednesday morning. By afternoon, watch radar and upstream observations across northern and central Ohio rather than assuming storms will wait until Thursday.

Sources: NWS Cleveland forecast discussion, NWS Pittsburgh forecast discussion

Thursday: The main storm day for much of the region

Showers and thunderstorms should accompany the front through western Pennsylvania, eastern Ohio, northern West Virginia and western Maryland.

The environment may support damaging wind where storms encounter sufficient afternoon instability and wind shear. NWS Baltimore/Washington describes the severe threat as non-zero but emphasizes considerable uncertainty over the front’s timing and strength. A faster morning passage would limit instability; a slower arrival near peak heating would increase the chance of stronger storms.

Locally heavy rain is possible, especially if the front stalls over Ohio or storms repeatedly cross the same area. The available local discussions do not establish a widespread flash-flood threat, so CAWA should avoid leading with flooding unless later WPC guidance or rainfall trends support it.

Prepare for possible active coverage Thursday. Check the latest official SPC outlooks and WPC excessive-rainfall outlooks before publishing a more specific threat area.

Sources: NWS Baltimore/Washington forecast discussion, NWS Cleveland forecast discussion

Friday: Cooler air returns

The front should move south and east, allowing cooler and less humid air to spread across eastern Ohio and western Pennsylvania. Showers could linger early in West Virginia or western Maryland if the boundary moves more slowly than forecast.

Check southern and eastern counties Friday morning. If the front has cleared, routine coverage can resume.

Saturday and Sunday: Warmer again

Saturday looks mainly dry and comfortable. The upper-level ridge is expected to rebuild during the weekend, bringing warmer conditions by Sunday.

There is no clear organized hazard signal at this range. Confidence in the general warming trend is moderate; confidence in exact temperatures and humidity is lower.

Routine monitoring should cover Saturday. On Sunday, check whether the returning heat and humidity will carry into the following workweek.

Operational meteorology and communication updates

NWS is considering making CAP its primary alert format

Status: Proposal open for comment through September 21, 2026

On September 1, the National Weather Service requested initial feedback on transitioning watch, warning and advisory dissemination to the Common Alerting Protocol, or CAP, as its primary format. The proposal could eventually discontinue traditional VTEC-formatted products, although CAP messages would retain event tracking, calls to action and impact-based warning information.

This could be a major change for any CAWA system that parses raw warning text or uses VTEC strings to identify events, updates and cancellations. CAP offers better support for structured and geospatial information, but a complete transition would require careful testing.

CAWA should inventory which tools read VTEC directly and which already consume CAP or the NWS API. Automated warning posts must continue recognizing corrections, extensions, upgrades and cancellations—not merely the initial alert.

No production workflow should change yet. This is an early proposal, not an announced implementation.

Source: NWS CAP transition proposal

NEXRAD Level II address changes September 15

Status: Scheduled implementation

NWS will discontinue the current NEXRAD Level II directory on NOMADS at 1200 UTC September 15. Identical files are already available from the replacement TGFTP location. Level III radar products are not affected.

Any CAWA downloader using the retiring NOMADS address will stop receiving Level II files unless its URL is changed. The format and filenames are staying the same, so this should be a straightforward migration.

Check radar scripts this week and add a freshness alarm if one is not already present. A feed that silently stops updating is more dangerous than one that fails visibly.

Source: NEXRAD Level II migration notice

RRFS and REFS testing should continue

Status: Operational implementation scheduled for October 6

NCEP still plans to introduce RRFS and REFS on October 6, alongside the retirement of NAM, SREF, HREF, HiresW and NAM MOS. Parallel RRFS and REFS data are available for testing.

The Wednesday-night and Thursday storm setup offers another useful comparison opportunity. CAWA can examine simulated reflectivity, updraft-helicity guidance and ensemble precipitation probabilities without treating the parallel system as established operational truth.

Continue auditing scripts, dashboards and graphics for dependencies on the retiring model families.

Source: RRFS and REFS implementation notice

WPC’s ERO comment period has ended

Status: Proposal awaiting a decision

Public comment closed September 5 on WPC’s proposal to add an Enhanced Risk category to the Excessive Rainfall Outlook, creating a five-level scale. No implementation decision is identified here.

CAWA should leave existing ERO graphics and category parsing unchanged until NWS publishes a formal decision and effective date.

Source: WPC Excessive Rainfall Outlook proposal

September 7, 2026

CAWA Weekly Meteorology Brief – August 31, 2026

August 31, 2026

Summary:

Heat and humidity will take over much of Central Appalachia this week. Wednesday should be the hottest day around western Pennsylvania and eastern Ohio, while dangerous heat may last into Thursday across parts of West Virginia and western Maryland.

There will also be several chances for thunderstorms. Instead of one clearly defined system, multiple disturbances will travel around the northern side of the heat ridge. That makes the forecast unusually dependent on the timing and track of individual storm complexes.

Tuesday deserves some attention across the northern part of the region, but Thursday currently looks like the most concerning day overall. Strong or severe storms may then continue into Friday, particularly across West Virginia and western Maryland.

Damaging winds and torrential rainfall appear to be the main concerns. Flash flooding could become more likely in places hit by repeated storms.

The week in brief

Monday: A few showers remain possible, but widespread hazardous weather is not expected.
Tuesday: Hotter weather arrives, with a conditional severe threat across the northern part of the region.
Wednesday: This should be the hottest day of the week. Storm chances may increase later in the day or at night.
Thursday: This currently looks like the best opportunity for organized severe thunderstorms and flash flooding.
Friday: The severe and flooding threat may shift into West Virginia and western Maryland.
Saturday: Most locations should improve, but showers or storms may linger in the mountains.
Sunday: Cooler and generally quiet weather is expected.

Storm timing may change considerably as the week unfolds. Residents should continue checking the forecast and make sure they have more than one way to receive warnings.

Full technical briefing

Monday night

Cloud cover kept temperatures lower than originally expected across much of the region Monday. Any showers left this evening should be isolated and light, although a brief thunderstorm is still possible near Wheeling, Morgantown and the surrounding ridges.

Patchy fog may develop overnight in West Virginia’s sheltered valleys. Elkins has the best chance of seeing dense fog or very low visibility.

Routine monitoring should be enough tonight. Watch for fog-related travel issues in the deeper mountain valleys early Tuesday morning.

Sources: NWS Pittsburgh forecast discussion and NWS Charleston forecast discussion.

Tuesday

Temperatures will rise into the middle 80s and lower 90s, with heat indices climbing into the middle or upper 90s around western Pennsylvania and parts of eastern Ohio.

NWS Cleveland has issued a Heat Advisory from Tuesday afternoon through Wednesday for locations generally along and west of a Cleveland–Akron–Wooster–Mount Vernon line. Most of CAWA’s eastern Ohio counties are not included right now, although the advisory could be expanded farther east Wednesday.

The severe-weather forecast is less certain. The atmosphere around western Pennsylvania may contain 2,000–3,000 J/kg of MLCAPE by late afternoon. That is plenty of instability, but warm air aloft and limited forcing may prevent storms from developing.

If storms do form, they could quickly become strong or severe. The best opportunity currently appears to be across northeastern Ohio, northwestern Pennsylvania and locations farther northeast. Another round could approach the northern part of the region Tuesday night.

Keep an eye on the northern counties Tuesday afternoon and evening. Check the strength of the cap, lake-breeze boundaries and approaching shortwaves before increasing the public severe-weather message.

Sources: NWS Cleveland forecast discussion and NWS Pittsburgh forecast discussion.

Wednesday

Wednesday should bring the hottest weather of the week. Most places outside the mountains will reach the upper 80s or 90s.

Heat indices around Pittsburgh should reach the middle or upper 90s. Parts of West Virginia and western Maryland may exceed 100°F, with a few locations possibly approaching 105°F.

NWS Charleston says advisory-level heat may develop across much of the lowlands. NWS Baltimore/Washington is also forecasting widespread heat indices between 100°F and 105°F Wednesday.

The heat ridge should keep most of the day dry, but another disturbance may arrive Wednesday evening or Wednesday night. If storms organize, they could bring damaging winds and very heavy rain.

Prepare heat-safety graphics and messaging before Wednesday afternoon. Storm coverage is still too uncertain for aggressive messaging, but radar and upstream observations will need closer attention later in the day.

Source: NWS Baltimore/Washington forecast discussion.

Thursday

Thursday is the day we are watching most closely.

A cold front and stronger disturbance will begin breaking down the heat ridge. At the same time, increasing northwest flow should bring stronger wind shear into a hot and unstable air mass.

That combination may support organized clusters of severe thunderstorms. Damaging winds currently appear to be the main concern, but torrential rain, frequent lightning and isolated hail will also be possible. Training or repeated storms could lead to flash flooding.

NWS Baltimore/Washington says the environment may support significant severe thunderstorms. Experimental AI and machine-learning guidance currently favors Thursday, although the exact timing and placement of storms remain uncertain.

What happens Wednesday night could change Thursday’s forecast. Early storms might stabilize the atmosphere and reduce the later threat. They could also leave boundaries behind that help new storms organize.

Dangerous heat may continue before storms arrive, especially in West Virginia and western Maryland.

Plan for possible active coverage Thursday. Confirm staff availability, prepare graphics and test the alerting dashboard ahead of time. A final decision on activating Storm Mode should wait until the timing and storm corridor become clearer.

Friday

The front may move slowly enough to keep thunderstorms in the region Friday. By then, the greatest concern should be shifting toward southern Pennsylvania, West Virginia and western Maryland.

Areas that receive heavy rain Thursday could be more vulnerable to flooding Friday. Damaging winds would also remain possible if another organized storm complex develops.

Treat Thursday and Friday as one possible multi-day operation rather than two separate threats. Keep track of rainfall totals, flooded locations and areas affected by repeated storms.

Saturday

Cooler and less humid air should begin moving into western Pennsylvania and eastern Ohio. The front may take longer to clear West Virginia and western Maryland, leaving a chance of additional showers or thunderstorms there.

Continue monitoring the southern and eastern parts of the coverage area until the front fully clears. Routine coverage should be enough elsewhere.

Sunday

High pressure should bring seasonable temperatures, lower humidity and generally quiet weather.

Return to normal forecast coverage unless the front stalls farther north than expected.

Seven-day outlook

Day	Main concern	What CAWA should do
Monday	Isolated shower and overnight valley fog	Routine monitoring is enough
Tuesday	Heat and conditional northern severe storms	Watch the northern counties during the afternoon and evening
Wednesday	Peak heat; storms possible later	Prepare heat messaging and monitor upstream storms
Thursday	Organized severe storms and flash flooding	Plan for possible active coverage
Friday	Continued severe and flooding potential	Track rainfall and repeated storm corridors
Saturday	Lingering storms south and east	Monitor mountain and southern counties until the front clears
Sunday	No significant hazard identified	Return to normal coverage

Changes CAWA should know about

RRFS and REFS arrive October 6

NCEP plans to place the Rapid Refresh Forecast System and RRFS Ensemble Forecast System into operations on October 6.

The deterministic RRFS will provide hourly, convection-allowing forecasts across North America at roughly 3-km resolution. The main forecast cycles will extend to 84 hours, while the other hourly cycles will run to 18 hours.

REFS will provide ensemble guidance through 60 hours. Its output will include probability fields, ensemble-agreement products and flash-flood recurrence-interval probabilities.

Parallel RRFS and REFS data are already available, giving forecasters time to evaluate the new guidance before it becomes operational.

For CAWA, the best next step is to compare RRFS and REFS forecasts against observations during this week’s storms. Simulated reflectivity, updraft helicity and precipitation forecasts are good places to start. REFS probabilities should also be compared with HREF before they are used in public messaging.

Read the official RRFS and REFS implementation notice.

Several familiar models are being retired

When RRFS and REFS become operational, NCEP will discontinue the NAM, NAM Nest, NAM MOS, SREF, HREF and most HiresW products.

This is more than a change in model preference. Scripts and dashboards that request those files may stop working entirely on October 6. Some fields will not have identical replacements in the new systems.

CAWA should search its tools and configuration files for references to nam, namnest, sref, href and hiresw. The severe-weather scoring program uses GFS as its main model source, but it is still worth confirming that it does not contain a legacy-model fallback.

Read the official model-retirement notice.

NEXRAD Level II data are moving

NWS will stop distributing NEXRAD Level II files through the current NOMADS directory on September 15. Identical files are already available from the replacement TGFTP location.

The format, filenames and update frequency are not changing. Level III radar data are also unaffected.

Any CAWA radar downloader using the old NOMADS directory will need its URL changed. A freshness check would also help catch situations where a feed silently stops updating.

CAWA’s RainViewer-based display is not directly affected by this change.

Read the official NEXRAD migration notice.

WPC is considering a fifth excessive-rainfall category

WPC is considering adding an Enhanced Risk category to the Excessive Rainfall Outlook. The proposed scale would be:

Marginal — 5%
Slight — 15%
Enhanced — 25%
Moderate — 40%
High — 70%

The public-comment period ends September 5.

An Enhanced Risk could be useful for Appalachian flood events that are more concerning than a routine Slight Risk but do not warrant the stronger Moderate Risk signal.

The possible drawback is confusion. Someone could see “Level 3” on both the SPC and WPC outlooks and assume they carry the same probability or meaning.

CAWA should not change its risk graphics or automated parsing unless WPC formally approves the new system. However, this is the final week to submit feedback.

Read the official WPC proposal.

What CAWA should focus on this week

The immediate concern is the heat from Tuesday through Thursday. Heat messaging should be ready before the most dangerous conditions arrive.

Tuesday’s severe threat needs to be monitored, but it is still too conditional for aggressive messaging. Thursday and Friday deserve more advance preparation. CAWA should be ready to increase coverage if confidence continues to grow.

Behind the scenes, this is also a good week to begin testing RRFS and REFS, check for legacy-model dependencies and confirm that no CAWA radar tool uses the retiring NEXRAD Level II address.

This briefing is intended for planning and situational awareness. It is not an official warning or a replacement for National Weather Service forecasts, watches or warnings. Conditions can change quickly. Visit weather.gov for current hazard information. This post was created with AI assistance.

August 31, 2026