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.
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