Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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350 FXUS61 KPBZ 180510 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 110 AM EDT Wed Sep 18 2024 .SYNOPSIS... Some limited rain chances, best in the ridges southeast of Pittsburgh, will be present into Wednesday night thanks to slow-moving low pressure. Rainfall should be light in most cases. Dry weather returns for Thursday and through the weekend. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... KEY MESSAGES: - Best rain chances along east-facing slopes tonight; more limited towards Pittsburgh - Above-normal overnight lows are forecast ------------------------------------------------------------------- Evening update...biggest question is how far east any overnight showers will be able to reach. Much of the latest model data is keeping the best chance for rain over the ridges and low lands on the western edges. Additionally, the eastward movement of the showers have slowed from previous runs. Tried not to stray too far from the previous forecast, but have slowed the westward progression of the PoPs. Rest of the forecast is in good shape. Previous discussion... Vertically-stacked low pressure continues to rotate in the vicinity of the Carolinas, and will continue to do so through tonight. As moisture and vorticity lobes continue to lift northward with time, some modest rain chances will eventually reach to a Zanesville/Pittsburgh/Indiana PA line tonight. However, the previously mentioned challenges of dry air and downslope flow, plus little northward progress of the surface system, will tend to keep rainfall spotty and light for the most part. Upslope- prone areas, particularly eastern Tucker County, have the best chance of getting meaningful rain. The cloud increase will keep temperatures 5 to 10 degrees above climatology tonight. && .SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY NIGHT/... KEY MESSAGES: - Low rain chances expand across area Wednesday, still highest in the ridges - Dry weather returns by Thursday - Seasonable temperatures Wednesday, returning to above average readings by Thursday ------------------------------------------------------------------- The slow-moving, stacked low pressure system will continue to rotate in the general vicinity of the Carolinas through Wednesday, before opening up into a broader trough that will position itself over the Mid-Atlantic and New England areas by Thursday. Moisture/vorticity lobes will continue to rotate around the low, reaching further north into our region by Wednesday, such that most of the CWA has at least a mentionable chance of measurable rain. By Wednesday night, as the eastward transition of the system takes place, rain chances drop off in coverage, largely limited to the ridges, before ending on Thursday as a developing ridge starts to push up the Ohio Valley. The models continue the overall bleak outlook for wetting rain for many locations. When looking at the potential for 0.10" or more of rain over the entire event, the 13Z NBM keeps 50 percent or greater probabilities near and to the south of I-70, with eastern Tucker County still seeing the best chances (here, there is a 50/50 shot of a half-inch). Locations north of I-80 have a slightly higher than even chance of seeing no measurable rain whatsoever. The expected cloud cover and potential light rain will limit the diurnal temperature range Wednesday/Wednesday night, with highs near climatology and lows a touch above normal. Decreasing clouds on Thursday will lead to a warmer day, with values going above normal once again. && .LONG TERM /FRIDAY THROUGH TUESDAY/... KEY MESSAGES: - Dry weather through the weekend, very low rain chances early next week - Above average temperatures through early next week ------------------------------------------------------------------- Model ensembles are in good agreement that the developing ridge to our west will slowly build eastward, extending from the Texas Gulf coast into eastern Canada by Saturday. This will also push the East Coast trough further offshore with time. As a result, dry weather and above-normal temperatures are forecast for Friday through Sunday with high confidence. Uncertainty ticks up a bit with the new work week. A new trough approaching from the Northern Plains/Upper Midwest has at least some potential to weaken the ridge during the Monday/Tuesday period, which would lead to cooler temperatures and an uptick in rain chances. However, cluster analysis shows that the majority of ensemble members largely maintain the ridge over our region, which would tend to keep the dry and warmer-than-normal pattern going. For now, the forecast for early next week will lean towards this latter scenario, pending future model runs. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... VFR is expected overnight with mid and high cloud cigs on the northern side of a low pressure system, which was centered across the western Carolinas. The low will drift toward the Mid Atlantic region today, as moisture and ascent/vorticity advection rotate around it. Expect a lowering cig, as moisture increases in the lower and mid levels. Most airports will see a cig at or below 5kft east of a BVI-HLG line. LBE and MGW should see MVFR cigs developing by mid morning, with better low level moisture and limited rain chances. Any MVFR should return to VFR by late afternoon/early evening, as lower level moisture begins to decrease. A persistent east wind is expected at around 5 kt. .Outlook... Occasional restrictions and showers are possible, especially near MGW/LBE, through early Thursday, as the low slowly tracks across the Lower Ohio Valley and Appalachians region. VFR is then expected through Sunday as high pressure builds in. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...CL NEAR TERM...22/CL SHORT TERM...CL LONG TERM...CL AVIATION...WM