Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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813 FXUS61 KPBZ 102235 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 635 PM EDT Fri May 10 2024 .SYNOPSIS... Dry conditions and mostly clear skies are expected overnight ahead of approaching low pressure that will return showers and thunderstorms for Saturday and lingering into Sunday. Temperatures will be below average this weekend. Warmer pattern returns next week with rain chances increasing again for Tuesday and Wednesday. && .NEAR TERM /THROUGH SATURDAY/... KEY MESSAGES: - Showers tapering off this evening with areas of fog possible by sunrise. - Lows tonight 5-10 degrees below average. ------------------------------------------------------------------- Forcing and daytime instability will be lost tonight as dry air wins out and brief shortwave ridging builds, dry conditions will ensue. Light wind will flip southerly overnight as a southwesterly gradient establishes ahead of approaching low pressure. Low temperatures tonight will dip into the low 40s and perhaps even upper 30s areawide which is a good 5 to 10 degrees below normal. With lingering low level moisture and light wind overnight, fog may form toward sunrise east of I-79. Some dense fog may be possible for areas that clear out and in river valleys through PA and WV. The current aurora forecast favors mostly clear skies overnight west of and including the Pittsburgh metro. With fog mentions more limited the farther west you go, viewing conditions should remain favorable should the auroras materialize in eastern Ohio. Viewing conditions will deteriorate the farther east you travel into PA and WV with fog and low stratus. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... KEY MESSAGES: - Warm front followed quickly by a cold front brings another shot of showers and thunderstorms. - Highs nearly 10 degrees below average. ------------------------------------------------------------------- Another upper wave dives southeast out of the Great Lakes Saturday as aforementioned low pressure tracks by to our north and its warm front reintroduces rain showers. Hi res ensemble timing is in good agreement on arrival of precipitation into eastern OH after 11am, PIT 2pm, and the ridges 3pm with even the earliest and latest timing only an hour to two on either side of the most likely. Overall totals with the warm advection driven precip should be light between 0.2-0.3". The cold front then arrives quickly after leaving us little time in the open warm sector. Southerly gradient flow will try to pull in warmer and more moist air but only have a short window to do so. Scattering of the cloud deck appears low probability, so this should help to keep instability in check ahead of the cold front. That said, hi res ensemble mean CAPE values range from 400-600 J/kg across the area with the 90th percentile closer to 900 J/kg (contingent on low probability clearing). Effective shear values should reach 20-25 knots and mostly southeasterly unidirectional. Combined with decent low and mid level lapse rates of 7-8 C/km, the environment may be able to support some gusty wind and small hail from the taller cores that manage to develop. Probability of exceeding 0.5"/hour rainfall rates are sub 30%. With clouds being dominant for most of the day and rain arriving by late morning, erred slightly below NBM for highs which should be just around either side of the 60 degree mark. Scattered showers may linger into the day on Sunday as the core of the 500 mb low gets closer overhead and the occluding surface low throws a weak trough across the area with lingering low level moisture. Additional rainfall totals look minimal and highest totals will be along the ridges with upslope enhancement. High pressure wins out by late afternoon with dry weather returning. && .LONG TERM /MONDAY THROUGH FRIDAY/... KEY MESSAGES: - Temperatures rebound into next week. - Showers and thunderstorms return Tuesday/Wednesday. ------------------------------------------------------------------- Upper ridging takes hold come Monday with surface high pressure establishing to our southeast. Uncertainty with the depth of an upper low well off to our north in Canada lends low confidence precipitation chances north of I-80. The most likely ensemble solution brings light rain there for the first half of the day, though a less likely solution with a weaker low would keep the rain further north. Pittsburgh and south should stay dry regardless. More widespread rain chances then arrive for Tuesday and Wednesday as low pressure ejects out of the Plains and high pressure breaks down. At this point, machine learning doesn`t indicate any potential for severe weather. Ensemble total precipitation sits around a 30-60% chance of >0.5" by Wednesday night. Tuesday will be the coolest day of the week owing to plentiful cloud cover and precipitation. Much more ensemble spread is exhibited by the latter half of the week with a developing trough to our west, but a dry period to close out the week with rain returning for the weekend looks more likely than not. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Light rain showers, increasing in coverage between 18z-22z, rising cig heights are expected through this evening. Intrusion of drier air as low pressure exits east will erode showers and cigs during the early evening hours, resulting in areawide VFR conditions. The combination of residual boundary layer moisture, some cig deck clearing, and light wind may promote fog formation during the pre-dawn hours Saturday morning. Highest probabilities are along the higher terrain east/southeast of KPIT where daytime showers will linger longest and drier air will be late on arrival (KMGW/KLBE/KDUJ). A cold front will approach from the NW at the end of the TAF period, producing a swath of light rain showers with low probability for thunder. .Outlook... Additional restrictions are likely in conjunction with the mentioned showers and low probability thunderstorms above. Scattered light rain showers will linger into Saturday night as the upper trough axis crosses. VFR returns Sunday and Monday under high pressure, before low pressure returns restriction and precipitation potential on Tuesday. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...MLB/Milcarek NEAR TERM...MLB/Milcarek SHORT TERM...MLB LONG TERM...MLB AVIATION...Frazier