Area Forecast Discussion
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439 FXUS61 KPBZ 201628 AAC AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 1228 PM EDT Tue Mar 20 2018 .SYNOPSIS... A wintry mix of precipitation is expected today with low pressure. The mix should change to snow tonight before gradually tapering off Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The 12Z RAOB at KPBZ indicated a warm layer present in a sharp dry layer. However ongoing precipitation will lead to its erosion via wet-bulb effect and ely cold air advection. As one might expect from such an evolution, initial freezing rain has been widely supplanted by sleet, with the ridges changed over to all snow. Reports of ice accrual have come in along the nrn fringe of the current precipitation band, where dry low-level air is helping wet-bulb temperature to remain below freezing. Given the current reports of slippery conditions in several locations, ice accrual in valleys of WV and ice accrual at ASOS sites, a short-duration Winter Weather Advisory has been issued from far-ern OH to wrn Preston County through this afternoon, until FZRA threat subsides. Little in the way of warming is expected today as overcast sky and ely wind will reinforce current sfc temperature in the low- mid 30s. Temperature may warm slightly N of I-80, where precipitation is slowest/least likely to arrive. The morning precipitation will diminish this afternoon as the associated upper wave weakens ahead of a second wave, which will strengthen tonight and provide renewed snowfall.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/... A second low is progged to dig across the OH/TN Valleys tonight and part of Wed. Cold advection in the wake of the initial Tue low should result in all snow across the region. Accumulating snow is expected as temperature drops below freezing at night. A non-trivial ely H8 wind anomaly will supply increasing moisture into the ridges, where snow totals were increased over the previous 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. Headlines generally were kept intact. Only adjustment was to expand the Winter Storm Warning to the Westmoreland County Ridges, where snow has already commenced. The snow should taper off from N-S Wed as lift/upper support shift off the east coast with a developing coastal low. Dry weather returns with shortwave ridging Wed night and Thu. Below-average temperature is expected to persevere. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Surface ridging should maintain dry weather until a srn-stream low returns rain and snow chances S of I-80 Sat thru early Sun night. Limited PoPs to chance with a significant model shift swd with the low in recent solutions. An ern-CONUS ridge should return dry weather later Sun and part of Mon before a Midwest trough returns low precip chances late Mon. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... Conditions will continue to deteriorate as precipitation spreads north and low levels. KMGW should remain all rain however, ports to the north will see a wintry mix eventually changing over to all snow and IFR restrictions by early afternoon. Improvement to low MVFR late afternoon through the evening until snow coverage increases again as a second sfc low approaches the region. OUTLOOK... Restrictions, albeit with gradual improvement, are likely into Thursday morning. && .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...Winter Storm Warning until 8 PM EDT Wednesday for MDZ001. OH...Winter Weather Advisory from 8 PM this evening to 8 PM EDT Wednesday for OHZ039>041-048>050-057>059-068-069. Winter Weather Advisory until 5 PM EDT this afternoon for OHZ050. PA...Winter Weather Advisory from 8 PM this evening to 8 PM EDT Wednesday for PAZ013-014-020>023-029-031-073-075. Winter Storm Warning until 8 PM EDT Wednesday for PAZ074-076. Winter Weather Advisory until 5 PM EDT this afternoon for PAZ014-020>023-029-031-073-075. WV...Winter Weather Advisory from 8 PM this evening to 8 PM EDT Wednesday for WVZ001>004-012-021-509. Winter Storm Warning until 8 PM EDT Wednesday for WVZ512>514. Winter Weather Advisory until 5 PM EDT this afternoon for WVZ001-002-509>511. Winter Storm Warning from 8 PM this evening to 8 PM EDT Wednesday for WVZ510-511.
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