Area Forecast Discussion
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125 FXUS61 KPBZ 162203 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 603 PM EDT Fri Mar 16 2018 .SYNOPSIS... High pressure will build into the region through this evening. Gusty northwesterly wind will subside toward sunset as temperature falls amid clearing sky. Wintry precipitation could clip northern West Virginia, southeastern Ohio and the ridges on Saturday. && .NEAR TERM /THROUGH SATURDAY/...
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Updated hourly temperature and dewpoint curves for the evening, as well as making some minor adjustments to sky cover. Lower clouds in the northeastern CWA continue to erode as high pressure builds in, albeit briefly. Previous discussion... Temperature tonight will remain considerably-below seasonal average as prime radiational cooling conditions will support a rapid loss of heat this evening. Occluding low pressure currently in the Plains states will be weakened by the stagnant upper ridge across the Dakotas, and will accelerate ewd tomorrow as it is absorbed into the stronger mid-level flow. Warm advection in advance of this wave will support the development of light precipitation approaching the srn zones beginning near dawn. The NAM and GFS/ECMWF models differ in their depiction of the thermal profiles with this system, with the GFS/ECMWF remaining cold (yielding all snow) while the NAM identifies a warm layer aloft (yielding a wintry mix of sleet and snow and possibly light freezing rain, although the nwd extent of the FZRA may be very close to the CWA border with RLX). 12Z RAOBs from the Plains do show a strong warm layer aloft, offering some credence to the NAM`s depiction. However, if the GFS/ECMWF turn out to be correct, precipitation would remain all snow. The forecast for tonight sided more with the NAM, yielding predominantly sleet/snow/rain with freezing rain localized to the ridges/valleys where the forecasted warm layer is deepest and warmest. From ZZV to MGW, soundings suggest the warm layer is sufficiently elevated to yield sleet rather than FZRA. But modest shifts in the position of the system could tank this forecast. As far as headlines go, the ridge zones of Garrett, ern/wrn Tucker and ern Preston are expected to yield advisory-threshold wintry precipitation no matter the outcome (either light FZRA in the warmer case or all snow in the colder case), so a Winter Weather Advisory has been issued. Along the srn tier of counties, we have opted for a whites-of-its-eyes approach until a trend toward FZRA or all snow becomes clearer. If the precipitation remains predominantly sleet as expected, it will cut down considerably on accumulation totals. As precipitation winds down and cloud cover breaks, there may be additional heating toward day`s end, which is why Sat maxima have been forecasted in the mid-upper 30s.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... Amid building high pressure, Sun and Mon will feature generally- sunny sky and little chance of precipitation given drying air and subsident upper levels. Temperature will rebound to near seasonal level ahead of an upper-level wave exiting the srn Plains. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... GFS Ensemble members disagree on the strength and precise path of a srn Plains trough exiting into the Appalachians, but generally identify the presence of a broad ern-CONUS trough ensconcing cold air in the region for the latter half of the coming week. As this srn Plains system approaches, a wintry combination of rain/snow and ice can be expected Tue/Wed, but details will depend on the position and placement. Thereafter, the system will transfer to a coastal low with waning precipitation locally. && .AVIATION /22Z FRIDAY THROUGH WEDNESDAY/... MVFR stratocu confined largely to the broad band emanating from Lakes Huron and Erie impacting FKL/DUJ and (at times) LBE. Outside of this area, light snow has all but ceased, the mid- level winds have started to back towards the west and warmer/drier air is moving in, quickly eviscerating the stratocu. VFR conditions under mostly-clear sky are expected this evening into the early overnight period. Another system will encroach from the southwest early Saturday, bringing the potential for snow and sleet for southern ports of ZZV and MGW. MVFR ceilings and shower activity should remain mostly south of I-70, but cannot rule out a brief MVFR ceiling extending northward to PIT/AGC/HLG. IFR is not expected at this time. Gusty northwesterly surface flow is already beginning to dissipate as the pressure gradient slackens. This trend should continue overnight. OUTLOOK... High pressure will limit restriction potential for Sunday and Monday. Low pressure will arrive Tuesday, bringing restrictions lasting through mid-week. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Winter Weather Advisory from 4 AM to 6 PM EDT Saturday for MDZ001. OH...None. PA...None. WV...Winter Weather Advisory from 4 AM to 6 PM EDT Saturday for WVZ512>514. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.