Area Forecast Discussion
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000 FXUS61 KPBZ 211715 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 115 PM EDT Sun May 21 2017 .SYNOPSIS...
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Periods of rain and some thunderstorms will continue until the passage of the cold front overnight. Rain chances will return Tuesday with the approach of mid-atlantic low pressure.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Update made to make small adjustments to the PoPs and temperatures based on radar and satellite coverage. Area of rain, associated with a shortwave ahead of the cold front, will slowly move across the region through the afternoon. With limited instability for thunderstorms expected, the mention of widespread thunder was taken out until later this afternoon/evening. A few embedded cells are still possible with this first wave, given the warming over the region with the lack of clouds early. Weak steering flow and ample moisture will support periods of heavy rain but the lack of strong ascent and high flash flood guidance values should generally limit widespread flood concerns. Still, a few localized water issues could arise in low spots or in areas of poor drainage through late this evening. Cold front, currently over Indiana, will slowly make it`s way toward the region this evening/overnight. Even with decent shear values, the timing of the front should limit available instability for strong/severe storms. Front should be aoa the ridges by Monday morning. With expected cloud cover and precipitation, temperatures both today and tonight should be just around or slightly above seasonal averages.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY/...
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Front should be almost through by Monday morning, with conditions improving under building high pressure through at least the start of Tuesday. The models continue to differ on the evolution of low pressure moving across the Tennessee valley on Tuesday. At this time, have opted to bump PoPs up based on some of the newer guidance and ensembles. Departure of this low will be quickly followed by yet another system, again which is being resolved a little differently between deterministic models. Opted to stay close to a model blend for midweek based on the uncertainty. Temperatures are expected to be near seasonal averages through the period.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... The broad trough will remain steadfast over the Great Lakes through the latter part of the work week. A re-enforcing trough will dig into the Midwest Wednesday, bringing increased rain chances that will linger into Thursday night. By the early part of next weekend, the Great Lakes trough is finally shunted off to the east by a weak ridge building into the Midwest. Temperatures will be at or below average through the latter half of the week, but will begin to climb into next weekend. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... Locally gusty southeast winds to around 20 knots will be the primary concern this morning across the higher elevation terminals, where early day sunshine has tapped a linger low level jet overnight. Otherwise, an upper level disturbance followed by a cold front will provide what should generally be two separate rain chances over the next 24 hours. Thickening/lowering clouds, and eventually areas of light showers will overspread the terminals from west to east by early afternoon. Upstream conditions suggest that pockets of MVFR conditions will accompany this first batch of rain. For now have removed thunder given the weak instability present in the generally mid level forcing present for this activity. Later this evening, a more strongly forced cold front will arrive with the likelihood for more locally heavy rainfall and thunderstorms in a narrow band of convection. Despite the time of day, the front should provide much stronger forcing to support brief downpours and thunderstorms in a narrow broken line of convection. IFR conditions may locally accompany this activity, although the time of year suggests that model guidance is much too pessimistic over the 24 hour period with the duration and degree of ceiling restrictions. Thus will maintain an MVFR outlook in the TAF for now. Improvement is expected later tonight (west) Monday morning (east) as winds shift westerly and skies quickly clear. .Outlook... The next chance for widespread restrictions and precipitation is expected Wednesday night into Thursday. Bookbinder && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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