Area Forecast Discussion
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000 FXUS61 KPBZ 170109 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 909 PM EDT Fri Mar 16 2018 .SYNOPSIS... High pressure will keep most of the night dry. Approaching low pressure should allow wintry precipitation to clip northern West Virginia, southeastern Ohio and the ridges on Saturday. && .NEAR TERM /THROUGH SATURDAY/... A few straggling stratocumulus are leaving the northern fringe of the CWA at present, leaving increasing cirrus over the rest of the area in a developing warm advection pattern. Temperatures have fallen off more quickly in areas, such as Franklin and DuBois, with fewer of these clouds, while areas to the south are a bit warmer. Still expect precipitation to arrive in the ZZV vicinity near or just after sunrise, as depicted in the majority of guidance. Making no changes at this time to the advisory or the expected weather types, as it seems prudent to allow the models to update with the 00Z sounding data. Looking at upstream soundings, particularly OAX, the NAM still appears to be doing a better job handling the warm layer aloft than the GFS. If this trend holds, it would point more to the wintry mix/freezing rain scenario for the southern counties rather than accumulating snow. Previous discussion ... 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. && .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 /01Z SATURDAY THROUGH WEDNESDAY/... Last of the stratocumulus will depart the vicinity of DUJ this evening. VFR conditions will continue through most of the night areawide, although mid and upper level clouds will be on the increase with time. The next system approaches Saturday morning, confining most of its impacts to areas south of PIT. There is still the potential of a snow and/or sleet mix at ZZV and MGW from midmorning through early afternoon, and freezing rain cannot be ruled out either. Ceilings in this area should bottom out at MVFR. Areas to the north should remain VFR, although a brief period of restriction at locations like HLG, AGC, and PIT is still within the realm of possibility. Winds will continue to slacken this evening, and remain variable or light out the northwest overnight and into Saturday. 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.