... Dry, mostly clear, and warm weather is expected through Thursday under high pressure. A potent Friday cold front will bring a pattern change, ushering in cool, wet, and gusty conditions for the weekend.
NEAR TERM /THROUGH TONIGHT/... Early Morning Update...A Special Weather Statement has been issued for much of the area along and east of the Ohio River for patchy dense fog, mainly concentrated in river valleys, through 9:30 AM local time. Motorists are urged to exercise caution when driving through fog and leave a safe following distance. Conditions are expected to improve after 9 AM. The rest of the forecast remains on track and details can be found in the previous discussion immediately below this update.
Previous Discussion...The persistent pattern of upper subsidence and surface high pressure continues under an anomalous eastern ridge. This will maintain pleasant, dry conditions through this evening and into tonight.
Continued dry conditions will mean that lower dew points will be present and also limit the amount of fog development. Development will still be confined to the river valleys and will impact roads near these areas. Any fog development will dissipate by 13Z.
Heading into the day, another day of light winds and mainly sunny skies will result in high temperatures once again nearing 10 degrees above average. As dry conditions and clear skies persist going into tonight, another night of patchy river valley fog is possible.
SHORT TERM /WEDNESDAY THROUGH THURSDAY/... As the ridge axis moves off of the coast on Wednesday and a central CONUS trough approaches from the west, the region will return to light southerly flow. High clouds may impinge from the west throughout the day. Warm flow will keep highs above average, roughly 10 to 13 degrees above average. Wednesday has the highest probability that temperatures exceed 80 in the Pittsburgh metro all week.
With the return of light nocturnal winds on Thursday morning, the fog probabilities will decrease, though patchy visibility obstructions are still possible.
The ridge will continue its progression offshore on Thursday. High cloud cover is anticipated to be a bit more robust, capping heating a bit in what is otherwise a very similar setup to the day prior. Probabilities greater than 50 percent of high temperatures exceeding 80 are only highlighted for the river valleys.
With stout high pressure to the east the approaching trough, added some pops to the northwest. However, it is possible given the antecedent conditions will yield a dry forecast for Thursday.
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... A deepening trough advances across the Plains/Midwest region. A lead shortwave ahead of the main trough, and its associated surface cold front, are progged to approach the region Thursday night. Rain chances are expected to escalate through the night from west to east with increasing moisture and ascent. Rain is likely on Friday into Friday night as the initial shortwave and cold front cross the Upper Ohio Valley region.
The surface cold front and initial shortwave should complete their passage Friday night. Cold advection will result in steep lapse rates Saturday and Sunday, as the deepening upper trough tracks across the Great Lakes and Upper Ohio Valley regions. This will result in scattered showers developing across the region. Instability in a strong pressure gradient will elevate wind gusts into Saturday and Sunday as well, particularly in any stout showers. Thus, the pattern and mesoscale conditions for Friday and Saturday would suggest a front undergoing frontolysis and model soundings showing a lessening of instability. have removed thunder as a possibility for these days and just left showers in the forecast.
850mb temperatures are currently progged to drop to 0 to 2 deg C by Saturday. Lake Erie water temperatures are around 20 deg C. Currently boundary layer wind progs would keep any lake enhancement to the showers north of the forecast area, with a WSW trajectory.
As this setup develops the low that pushed the trough across the Upper OH Valley reaches the ridge off the east coast and retrogrades west over the Great Lakes. This keeps a period, as mentioned above, winds out of the northwest keeping the potential for showers over the area for Sunday and Monday, invigorated each day with heating. Cooler air advected in behind the low will keep the potential for near freezing temps in the higher terrain. This setup will need monitored for any possible frost potential and perhaps a flurry.