Area Forecast Discussion
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000 FXUS61 KPBZ 211156 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 756 AM EDT Sun May 21 2017 ...UPDATED AVIATION DISCUSSION... .SYNOPSIS... Rain chances increase today ahead of a cold front arriving late tonight. Temperatures will be at or slightly below seasonal averages for most of next week. && .NEAR TERM /THROUGH TONIGHT/... Showers and thunderstorms will begin to move into the far western zones by 12-14Z. As the weakening pre-frontal wave lifts northeastward through the afternoon, rain chances will spread east. Thunderstorms are expected to develop, but will ultimately be limited in strength due to limited instability and weak forcing away from the parent low. Upper- level flow pattern will favor showers and thunderstorms moving southwest to northeast, quasi- parallel to a lagging cold front. Despite favorable moisture availability and cell motion, the aforementioned lack of strong ascent should keep precipitation efficiency from reaching a widespread flood concern. Still, a few localized water issues could arise in low spots or in areas of poor drainage through late this evening. With increasing clouds and rain chances, high temperatures will be moderated to just above averages. Lows tonight will remain above average, ahead of the approaching cold front. && .SHORT TERM /MONDAY THROUGH TUESDAY/... The large parent low pressure system will move through the western Great Lakes tonight, sweeping a cold front through our area Monday morning. The bulk of the remaining rain chances will be in the pre-dawn hours Monday, but a few showers could linger in the Ridges through midday. High pressure will begin to establish drier weather through Monday afternoon, despite a broad upper-level trough holding in the Great Lakes. Dry weather is expected to last through much of Tuesday. Some model differences exist on the northern extent of a system passing to our south Tuesday evening. For now, will continue to side with the drier solutions, ignoring the NAM as a fast and northern outlier. Temperatures are expected to be near seasonal averages Monday and Tuesday as we remain in southwesterly flow on the eastern periphery of the broad trough. && .LONG TERM /TUESDAY 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 /12Z SUNDAY THROUGH THURSDAY/...
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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
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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