Area Forecast Discussion
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000 FXUS61 KPBZ 210145 AAB AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 945 PM EDT Tue Mar 20 2018 .SYNOPSIS... Snow will continue overnight, before gradually tapering off Wednesday. && .NEAR TERM /THROUGH WEDNESDAY/... 945pm update...continue to update PoPs and snow totals overnight. Models have not handled evening snow development well at all. Expanded the cat PoPs late tonight with the passage of the main upper level trough. Previous discussion... This second low is progged to dig across the OH/TN Valleys tonight and part of Wed. Cold advection in the wake of the initial low should result in all snow across the region. Accumulating snow is expected as temperature drops below freezing at night. The highest snow rates will occur late tonight, from 3 AM to 10 AM roughly, as upward motion is maximized, and likely will pose a concern for the morning commute. A non-trivial, ely H8 wind anomaly will supply increasing moisture into the ridges, where snow totals were increased over the previous shift`s forecast. Otherwise, very few changes to snow totals were made. In general, 1-3" in ern OH, 2-5" from near PHD-LBE, 6-12" in the ridge zones, with localized 16-18" reports possible in the highest ridges. Less than 1" is expected N of I-80, where temp today will be highest and the least amount of precipitation is anticipated owing to lingering low- level dry air. Snow will wane quickly Wed afternoon as a coastal low pressure system intensifies. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... Dry weather returns amid shortwave ridging Wed night and Thu. Below-average temperature is expected to persevere as nwly flow supplies a steady source of cooler air. Some models indicate the passage on Fri of a shortwave trough in nwly flow. A lack of moisture may preclude snow showers, but this period may be one to watch for needed forecast adjustments. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... A srn-stream low is noted in most medium-range model forecasts during the Sat/Sun timeframe. However, the nrn extent to which its precipitation shield can spread differs by model. It does appear that the nrn-stream ridge building in the Great Lakes region over the weekend could limit its influence on the Ohio Valley, but a wintry mix is not out of the question. Upper-level wave breaking late in the weekend and eventual swly flow aloft will lead to a warm-up to near seasonal average beginning early next week. But such a pattern also will increase chances for precipitation. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... MVFR restrictions in the snow south of I-80 will continue into Wednesday. May see a brief respite this evening, as we hit a lull in the snow activity. A deterioration to IFR is possible late tonight/early Wed morning as precipitation coverage and intensity ramps up again. OUTLOOK... Restrictions, albeit with gradual improvement, are likely into Thursday morning. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Winter Storm Warning until 8 PM EDT Wednesday for MDZ001. OH...Winter Weather Advisory until 8 PM EDT Wednesday for OHZ039>041-048>050-057>059-068-069. PA...Winter Weather Advisory until 8 PM EDT Wednesday for PAZ013- 014-020>023-029-031-073-075. Winter Storm Warning until 8 PM EDT Wednesday for PAZ074-076. WV...Winter Weather Advisory until 8 PM EDT Wednesday for WVZ001>004-012-021-509. Winter Storm Warning until 8 PM EDT Wednesday for WVZ510>514. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.