Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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140 FXUS61 KPBZ 232345 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 745 PM EDT Mon Sep 23 2024 .SYNOPSIS... An active weather pattern is expected through most of the week with a Marginal Risk for severe weather on Tuesday south of Pittsburgh. Even with the clouds and threat of rain, temperatures will remain warm through the week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... KEY MESSAGES: - Scattered showers along a passing cold front this afternoon. - Dry period likely for most of the overnight. ------------------------------------------------------------------- Update... Reduced POPs east of PIT to slight chance, as shortwave supported lift has shifted east of the area. A cold front was analyzed from western NY, to west of LBE, to just west of MGW. This front will continue to drift eastward through this evening, though little additional shower activity is expected as the upper support has exited. Previous discussion... Behind the front, drier mid-level air works in and we should mostly lose the precip chances with for most of the overnight, save the higher elevations where upslope flow with lingering low-level moisture may provide some drizzle. Some areas of fog and low stratus are also on the table, especially where rain fell today, with sufficient low-level saturation. With the cloud coverage and elevated dew points, lows will fall to the low to mid 60s, some 10 degrees above normal. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/... KEY MESSAGES: - Rain chances continue through mid-week. - Marginal Risk (1/5) for severe weather on Tuesday. ------------------------------------------------------------------- Height falls ensue on Tuesday as the shortwave ridging is shunted east by a digging central CONUS trough. Another center of low pressure, this one perhaps slightly deeper than Monday`s, and associated shortwave energy will track just off to our west. This will bring another round of showers and thunderstorms. Deep layer southerly flow will advect in much higher, Gulf source moisture with ensemble mean precipitable water values in excess of 1.5" which is above the 90th percentile of climatology. A look at forecast soundings shows a deep warm cloud layer to ~13kft with high equilibrium levels and skinny CAPE. This favors efficient rainfall producers with warm rain processes. In addition, CAMs continue to hint at potential localized areas of higher totals with convective enhancement, but this is lower confidence. Hi res ensemble probability for >1" through Tuesday night does show strips of up to 40%, so the potential is there. Probability for at least 0.5" is between 40-80%. In addition, a lower probability severe threat is also a possibility. How much instability we can generate will be in question with morning cloud cover and showers, and there won`t be much mid-level dry air to work with owing to the saturated profile. Ensemble probability of >1000 J/kg of CAPE maximizes in the WV Panhandle/southeast OH, and northern WV at 40-60%. With dew points in the mid 60s and forecast highs in the low 70s, LCLs will be low and CAMs all show a veering low level wind profile as 850 mb flow increases by afternoon atop backed southeasterly surface flow. This presents a lower probability, conditional tornado threat. Machine learning also suggests a low end wind and tornado threat, and we remain outlined in a Marginal Risk (1/5) from Pittsburgh south. The initial digging trough is favored to cut off into a closed low across the south-central CONUS with some uncertainty in the timing and depth of a northern stream trough north of the Great Lakes on Wednesday. Rain chances will continue with rounds of shortwave and general troughiness in southwest flow. With generally weaker forcing, 24 hour totals ending Thursday morning look on the lighter side, mostly less than 0.5", though a much lower probability solution with a deeper, phased trough exists with higher amounts. Temperatures through mid-week will be cooler owing to increased cloud coverage and precipitation. && .LONG TERM /THURSDAY THROUGH MONDAY/... KEY MESSAGES: - Uncertainty increases greatly for the latter half of the week with potential tropical low interaction. - Rain chances will continue through the end of the week. ------------------------------------------------------------------- A weak boundary may pass through the area sometime Thursday, but seeing significant spread in the ensembles on the timing which will impact when we lose the rain chances. Ensemble clusters exhibit quite a bit of disagreement at this point with how the upper level pattern evolves. The central CONUS trough may interact with the remnants of now PTC 9 as it moves inland out of the Gulf. Meanwhile, the northern stream trough will be sliding across the Northeast states. Ensemble clusters all show that the remnants will be absorbed by the trough but with much uncertainty after that. The highest probability scenario at this time is that the northern stream trough deflects the remnants off to our west and rain chances here are lower. There are potential wetter solutions with a track further east, but until we get a better idea on the evolution, will stick with NBM given all of the uncertainty which advertises low end rain chances into the weekend. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Expect ample low level moisture to persist through the overnight behind a weak frontal boundary and little advection. This will give the potential for fog development overnight. The caveat is with the lingering cloud cover and this may result into a more stratus layer overnight resulting in IFR and below conditions. Showers and thunderstorms will become more numerous towards dawn and begin to move into the Ohio counties after dawn. have put PROB30s in to account for the uncertainty in coverage. There is expected to be another round developing towards the 16Z and 18Z period with additional convection continuing through 20Z. Restrictions are expected to be IFR and below at times through the morning and into the early afternoon, especially near thunderstorms. .Outlook... Rain and restriction chance continues into Tuesday with another low pressure center. Unsettled weather is then possible through mid-week. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...22/MLB NEAR TERM...WM/MLB SHORT TERM...MLB LONG TERM...MLB AVIATION...Shallenberger