Area Forecast Discussion
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000 FXUS61 KPBZ 160309 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1009 PM EST Thu Feb 15 2018 .SYNOPSIS... Low pressure and a cold front will result in widespread rain tonight. Precipitation should taper off Friday as the front exits. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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...Widespread Flooding Expected Through the Night... A band of training rainfall has worked its way north of Pittsburgh and gradually weakened a bit over the past couple of hours in conjunction with strong low level convergence on the nose of the 850 mb low level jet flow. Multi-model PWATs suggest we are in the neighborhood or exceedingly record levels of that variable in our area, so with strong forcing and deep moisture overlapping, it should be no surprise that heavy rainfall has resulted. Interwoven convective elements are propagating down this corridor, as well, in concert with some weak elevated instability. With that in mind, hi-res guidance generally likes the idea of shifting the band of best low level convergence slightly just slightly more northward over the next several hours before gradually translating it southward with the advance of an incoming frontal boundary. This will mean the heavy rainfall band should start to slowly meander back southward from its current location, yielding the highest amounts generally south of its current location. As a result, the best flooding chances will likely lie in this corridor as well as in the urban areas around Pittsburgh, Wheeling, Greensburg, and Washington. Multiple flood warnings are in effect for a vast region of the CWA as almost all area creeks are near or far exceeding bankful. Most of the rain should start to become constrained toward the southeastern portions of the area by morning as the frontal boundary advances southeastward. As it does so, the threat of flooding will lessen progressively from the northwest to southeast. Fries
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... Widespread coverage of rain will shift south and east of Pittsburgh by sunrise Friday, although precipitation will continue for several hours and most likely end as snow with falling temperatures during the day. However, it does not appear that colder air and moisture will overlap enough to allow for much, if any snowfall accumulation. After a warm day today, temperatures will be near or below freezing by sunset Friday. Dry weather should return Friday night and Saturday morning as high pressure slides east across the region. Similar to last night, models continue to struggle with low pressure and a cold front moving up the coast Saturday afternoon and night. Models have trended slightly farther west with the system, but still vary wildly in how much precipitation makes it into our region and how much stays to the southeast. Slightly backed off on snow amounts compared to previous forecast based on model depictions of QPF/snow, but this is a low confidence forecast. High pressure should return dry weather for Sunday. Temperatures should be near to a few degrees above seasonal levels. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Southwest flow between a Wrn CONUS trough, and a SE CONUS high should result in warm weather through the period. Shortwaves embedded in the flow, and proximity to a slow moving frontal boundary, should keep periodic rain chances through mid to late week. The warmest day of the week looks to be Tuesday, before the front arrives. Highs then could be well into the 70s for some locations. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... Rain (and possibly thunderstorms) will continue overnight across the TAF sites the next several hours. This will lead to MVFR conditions, and possibly temporary IFR conditions. Most sites will go to IFR conditions into the overnight hours, but eventually rain will come to an end by morning, with MVFR ceilings persisting well into the day. Winds tonight will remain out of the southwest with gusts of 20-25 knots, but there will be a wind shift overnight to the northwest, and some gusts may continue. Northwest winds of 10-15 knots (gusts to around 20 knots) will continue on Friday. OUTLOOK...MVFR conditions are expected to continue through Friday before clouds scatter out. MVFR conditions are possible again on Monday into Tuesday. && .HYDROLOGY... Widespread moderate to heavy rain should overspread the area this evening and through tonight as low pressure and a cold front approaches and crosses the area. Rainfall amounts are expected to range from around an one inch S of I 80, to around 2 inches across the N I 70 . The flood watch has been expanded N and W and various river flood watches for specific points along the Ohio and Mon rivers continue. The point at Pittsburgh is expected to rise to 18 ft Fri morning which affects the Mon Parking Wharf, and above flood stage, 25 ft, Sat morning. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Flood Watch through Friday afternoon for MDZ001. OH...Flood Watch through Friday afternoon for OHZ039>041-048>050- 057>059-068-069. PA...Flood Watch through Friday afternoon for PAZ013-014-020>023- 029-031-073>076. WV...Flood Watch through Friday afternoon for WVZ001>004-012-021- 509>514. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.