Area Forecast Discussion
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000 FXUS61 KPBZ 212004 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 304 PM EST Mon Jan 21 2019 .SYNOPSIS... Building high pressure will suppress residual snow showers later today. Precipitation chances return Tuesday night with approaching low pressure. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Continued wind chill headlines across the northeast zones as well as the WV/MD mountains as gusty winds continue coincident with two areas where temperatures have struggled to climb. Winds should gradually subside with sunset, but this will far and away go down as the coldest day of the early winter season thus far. Elsewhere, lake-effect cloud cover and a few passing flurries will steadily wane with the loss of daytime mixing and a loss of cross-lake trajectories as the center of an impressive 1038mb high spreads east tonight. Another bitterly cold night in store for the region. Expected overnight lows near or slightly below zero in most areas, and would not be surprised to see an isolated reading approach -10F in the protected Allegheny forest or the deep valleys of Preston/Tucker counties WV. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/... A 1040mb surface high will quickly shift east of the CWA early Tuesday morning, with strong low level warm advection expected beneath a transient mid level ridging. An impressive diurnal spread is expected, especially south and west of Pittsburgh where the snow pack is light to non-existent, and highs may approach 40 degrees late in the day. Highs should approach freezing around Pittsburgh, and will be restricted in the mid 20s across the I-80 corridor and into the eastern mountains where high pressure will hold out the longest. Temperatures will fall back early Tuesday evening before skies cloud up in advance of a deepening storm system over the Midwest. Very strong low-mid level warm advection will occur Tuesday night coincident with sharp pressure/height falls ahead of the deepening trough. Deep layer flow trajectories off the Gulf of Mexico will quickly reach the area on a 50 knot low level jet early Wednesday morning. Although all model solutions show a warm nose aloft, prefer the much warmer NAM solution given its typical handling of these types of systems. This suggests that precipitation will likely begin as rain* with perhaps some sleet across the far northeast at onset. The caveat is that we are coming out of a several day deep arctic plunge. Other than areas which reach the upper 30s tomorrow, surface temperatures will remain well below freezing at the onset. Having worked several events in my career in similar scenarios (arctic outbreak to rapid warmup), it is always a challenge figuring out when freezing rain will cease. With heavier precipitation arriving for the Wednesday morning commute, it`s key that we get this right and perhaps err on the side of caution. I`ve seen freezing rain accrue until air temperatures reach the lower 40s in prior arctic events, and thus will keep a mention of FZRA for areas north of I-70 as well as the WV/MD mountains through mid morning Wednesday despite hourly temperatures above freezing. Headlines may be necessary in that 06Z to 15Z. Rain, heavy at times, will continue through Wednesday and at least across the southeast zones into Wednesday evening as several lower tropospheric waves ridge through the mean trough position. Deep convection along the southwest tail of the frontal zone will only act to further moisten the local environment, with mid-upper moisture carried by a strong southwesterly jet. Not surprisingly, forecast precipitable water values in the 0.80 to 0.90" range are at the upper echelon of climatology for Jan 23rd, and I am expecting a widespread 0.75" to 1" of QPF for the region. This rainfall, coupled with snowmelt, on top of rapid ice growth on area rivers over the past 36 hours, yields a moderate to high confidence that hydrologic issues will follow for the mid-late week. A surface cold front will sweep across the region Wednesday night, but will be coincident with rapid dry advection aloft. Thus, expecting that any changeover to snow on the backside of the system will be inconsequential with maybe an inch or two max of upslope snow in the WV/MD mountains through Thursday morning. Bookbinder && .LONG TERM /THURSDAY THROUGH MONDAY/... The longer term period suggests a very high confidence of much below normal temperatures. Highly amplified ridging over the western US, coupled with an incredible sub 500dm vortex over southern Ontario, will lead to repeated clipper systems bringing periodic snows and a series of arctic intrusions. Cut guidance temperatures in the extended, perhaps not enough. Best chance for minor snow accumulations looks to be Saturday night, but could change given the speed of these systems embedded within a very fast polar jet branch. Bookbinder && .AVIATION /20Z MONDAY THROUGH SATURDAY/... Cold advection stratocu and lingering snow shower activity will dissipate this evening as upper level trough shift easts and surface ridging takes place. Until this time, ceilings will fluctuate between high MVFR and VFR though visibility should generally remain greater than 6sm. Pressure gradient will continue to slacken with wind gusts diminishing through the eve. NW wind will back to the SSW in advance of the next system. VFR prevails Tuesday. .Outlook... Restrictions will return late Tuesday/Wednesday with the next low pressure system. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Wind Chill Advisory until 7 PM EST this evening for MDZ001. OH...None. PA...Wind Chill Advisory until 7 PM EST this evening for PAZ008-009- 015-016. WV...Wind Chill Advisory until 7 PM EST this evening for WVZ512>514. && $$

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