Area Forecast Discussion
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000 FXUS61 KPBZ 152244 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 544 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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...Heavy Rainfall Developing Along and Just North of I-70... A strong band of training rainfall has managed to already develop late this afternoon just to the north of I-70 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 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 will be move likely to meander north then south of its current location, yielding the highest amounts in total generally near where it is current. 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. Flood Watches have already been hoisted, and radar trends are being closely monitored as minor flooding is already becoming evident in portions of Westmoreland County, especially. Fries
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
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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.
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&& .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 /00Z FRIDAY THROUGH TUESDAY/... High MVFR/low VFR cigs will persist for another hour or two before conditions deteriorate with the approach of an upper level shortwave. Rain will begin to spread into the region over the next couple of hours, with temporary vsby restrictions until the heavier precipitation reaches the area this evening. Made most of the adjustments to the terminals based on the placement of the heavier precip in the hi res model guidance. Still expect a period of IFR almost everywhere overnight as lift and thus precipitation rates are enhanced with the passing cold front. Improvement to MVFR is expected behind the front passage tomorrow though scattering out of the clouds is not likely until late. A wsw to nw wind shift will occur overnight. Gusts to 20+kts are possible tonight and Friday. && .HYDROLOGY... Widespread moderate to heavy rain should overspread the area this aftn and tonight as low pressure and a cold front approaches and crosses the area. Rainfall amounts are expected to range from around an inch N of I 80, to around 2 inches across the OH and Monongahela basins. 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. && $$

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