Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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393 FXUS61 KPBZ 260040 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 840 PM EDT Tue Jun 25 2024 .SYNOPSIS... Mainly dry weather is expected tonight. Strong to severe thunderstorms will be possible Wednesday afternoon and evening with a crossing cold front. Isolated flooding is also possible with heavy rainfall. Temperatures will trend upwards into the weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... KEY MESSAGES: - Mainly dry conditions are expected overnight, though light showers may be possible for some. - Mild temperatures with increasing humidity overnight. ------------------------------------------------------------------- Evening Update... Convective-allowing models have backed off on the chances for shower and storms overnight tonight in our area. The PIT 00Z sounding shows a dry deep-layer profile and with no development or even percolating occurring upstream, that solution is a bit more believable right now than the alternative. As such, lowered PoPs across much of the area at least through Midnight. Some light shower activity could be possible on the fringes of our area, primarily north of I-80 and over central/eastern Ohio, during later overnight hours and into Wednesday morning. Elsewhere, dry weather is expected tonight but mild temperatures and increasing humidity as moisture gradually returns from the west and dense cirrus prevents much radiative cooling. Previous Discussion... A mesoscale convection system (MCS) continues to dive south, within an elongated ridge. Precipitation chances have remained west of Pittsburgh due weak instability. There was a brief period of thunder near Coshocton/Muskingum County earlier, along the edge of the MCS. However the threat has subsided and rain showers remain. With increasing cloud coverage from outflow of the MCS and precipitation chances, temperatures north of I-70 will likely trend near average. Areas south may trend 5 degrees above average. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... KEY MESSAGES: - Showers and thunderstorms are likely Wednesday with a new disturbance. - All threats (flooding, tornadoes, hail, and wind) appear promising early afternoon through late evening. - Storm Prediction Center continues to have a Slight Risk for portions of our region, Weather Prediction Center continues the Marginal risk for flooding. ------------------------------------------------------------------- An ejecting shortwave out of the Midwest will regenerate showers and storms Wednesday across the Ohio River Valley. A few storms may be considered strong to severe if conditions permit, damaging wind gust and hail will be the main threat. However, the tornado threat is considered slightly above the climatological average given directional and vertical wind shear. Based on Hi-Res model ensembles, the joint probabilities of bulk wind shear (>= 30kts) and instability (CAPE >= 500J/kg) are elevated between the period of 1pm to 8pm Wednesday. However, storms could evolve as early as 10am under a warm, moist unstable air mass. The severe threat will likely evolve into a flooding threat as the day progresses, especially late evening with ongoing convection. With PWATS well above the climatological average (1.65" to 1.90") and training showers and storms under zonal flow, swaths of 1 to 2 inches may occur across the region Wednesday night. If these noted high amounts occur over urban areas in a short time period, flash flood products will need to be issued. The severe weather and flash flood threat will likely decrease after midnight as the shortwave tracks east. && .LONG TERM /THURSDAY THROUGH TUESDAY/... KEY MESSAGES: - Dry, quiet weather is expected Thursday. - Probability of above average temperatures increase Friday into Saturday. - Shower and thunderstorm chances return Saturday into Sunday with a new disturbance. ------------------------------------------------------------------- In the wake of Wednesday`s shortwave and associated front, temperatures return to normal and dry conditions resume as high pressure builds in across the region. A warming trend in temperatures is forecasted Friday and into the weekend as heights gradually rise, reaching about 588-590dm by Saturday. If showers and storms are absent for a prolonged period of time, apparent temperatures could range from 95F to 100F. However, confidence is still low on heat impacts given long range ensembles tracking a new trough over the Great Lakes and could stir strong to severe storms. Dry conditions and near to slightly above normal temperatures are forecast early next week as high pressure resumes control. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/... An upper level shortwave will approach the area late tonight into Wednesday with an associated surface cold front. Confidence is high that this wave will increase shower and thunderstorm coverage mainly after 18z on Wednesday, with showers then continuing until cold frontal passage around 06z Thursday. Confidence has increased in mainly dry conditions tonight through most of Wednesday morning, so have removed prior mention of showers and thunderstorms for that timeframe. There remains some uncertainty with timing of storm initiation after 18z. Afternoon storms will carry potential for damaging winds, large hail, and possibly isolated tornadoes. Southwesterly winds will diminish overnight, then gust 15-20kt Wednesday afternoon. Wind become northwesterly Wednesday night behind the front. .Outlook... Showers and thunderstorms will taper off Wednesday evening, though MVFR to IFR ceilings will linger with cold FROPA. High pressure and rising heights aloft is favored to support VFR and dry weather Thursday/Friday. The next upper level shortwave and surface cold front will increase thunderstorm and restriction chances Saturday. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Hefferan NEAR TERM...Cermak/Hefferan SHORT TERM...Hefferan LONG TERM...Hefferan AVIATION...Rackley/Frazier