Area Forecast Discussion
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000 FXUS61 KPBZ 151848 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 248 PM EDT Sun Apr 15 2018 .SYNOPSIS...
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Rain, heavy at times, will overspread the region by this evening and continue through tonight ahead of a cold front. Behind the front, showery precipitation and colder temperatures will dominate through the early part of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Precipitation has only grudgingly made eastward progress this afternoon, but this will change over the next few hours as the approaching trough starts to take on a negative tilt and a moist low-level jet starts to arrive. Elected to expand the Flash Flood Watch to encompass eastern Ohio and the northern WV panhandle. Model consensus of a band of 1.5 to 2.5 inch QPF, perhaps locally higher, was getting harder to ignore. The western counties fall under the right entrance region of a 120-140 knot upper jet during the late afternoon and evening as the trough tilts. Layered frontogenesis and deformation will also be present, along with anomalously high PWAT values of 1.3 to 1.4 inches. Although flash flood guidance values are fairly high in this area, felt that rain rates may support at least isolated flooding concerns. The watch is maintained over the original eastern counties as well where a period of training heavy showers is also possible. SPC still has the southern counties in a marginal risk for severe storms. Instability still looks meager overall, and have maintained only a slight chance of thunder. If any storms can root in the boundary layer, there is a short window where storms could take advantage of long hodographs to allow for gusty winds or a QLCS-type spinup. However, flooding possibilities are the main concern. The cold front will arrive in the western counties this evening and depart to the east during the predawn hours. Steadier rain will end, to be followed by more showery precipitation as the upper low makes its way into the Ohio Valley.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY/...
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The upper low will swing across the region behind the boundary on Monday. Periodic shortwaves will then rotate through in the troughing pattern through Tuesday, producing showery precipitation. A mix with and change to snow is still figured first along the higher ridges Monday, and then areawide Monday night into Tuesday morning. Boundary layer warming should allow rain to become dominant again in the lowlands Tuesday afternoon. Any snow accumulation should be minor given the time of year and the antecedent warm conditions. Below normal temperatures will persist.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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Precipitation will linger into Tuesday evening north of Pittsburgh, with a brief period of dry weather late Tuesday night into Wednesday in advance of low pressure moving into the region from the Plains. The low should pass just north of the area Thursday morning, sweeping a cold front through. While a flake can`t be ruled out north of I-80 with the initial precipitation, at this point it appears that all precipitation Wednesday night and Thursday would fall as rain. Before precipitation ends Friday, all locations will have a chance for snow Thursday night into Friday morning. High pressure building across the Great Lakes should then keep weather dry into the weekend. Temperatures will be below normal through the extended forecast.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/... Conditions will deteriorate to MVFR/IFR at all sites during the evening hours. Thought that all sites would experience gusts this afternoon, but in the 18Z TAFs pulled the mention of gusts from any terminal that hadn`t had any so far. With a low level jet present ahead of the cold front, have gone ahead and added a period of low level wind shear to all TAFs, although LLWS will likely occur for a shorter time period than is suggested in the current forecast. Even with a wind shift with the cold frontal passage, appears that conditions should remain MVFR at all terminals into Monday afternoon. OUTLOOK... MVFR is anticipated for Tuesday as the area will remain under an upper trough of low pressure. The next chance for restrictions will come late Wednesday and Thursday as another front crosses the area. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Flash Flood Watch through late tonight for MDZ001. OH...Flash Flood Watch through late tonight for OHZ039>041-048>050- 057>059-068-069. PA...Flash Flood Watch through late tonight for PAZ020-021-029-031- 073>076. WV...Flash Flood Watch through late tonight for WVZ001>004-012-021- 509>514. && $$

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