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FXUS61 KPBZ 101152 AFDPBZ

Area Forecast Discussion National Weather Service Pittsburgh PA 652 AM EST Sun Dec 10 2023

SYNOPSIS
Temperatures will fall behind a cold front today, with daytime rain mainly east of Pittsburgh. Rain will change over to snow tonight and linger into Monday along with blustery and chilly conditions. Several inches will accumulate in the ridges, with less elsewhere. Drier weather and moderating temperatures will follow for Tuesday.

NEAR TERM /UNTIL 6 PM THIS EVENING/
Cold front is near PIT at this writing, showing up well as a thin line of showers. Next slug of rain will lift ahead of the boundary to the east of Pittsburgh this morning. Lift is being supplied by a weak low pressure wave on the boundary, as well as by upper divergence courtesy of a 130-150 jet streak over the eastern Great Lakes. The cold front will exit the region by 12Z, but precipitation will continue through the afternoon in the ridges thanks to the surface wave. Portions of the far southeastern CWA are in line for an additional 0.5 to 0.75 inch of rain, while areas west of HLG and PIT will receive 0.10 inch or less today. This is generally in line with HRRR and WPC thoughts.

Maximum temperatures will be set during the morning hours today, as fairly stout cold advection will follow the boundary, leading to falling daytime values. Soundings west of Pittsburgh show a temperature structure that could support snow by this afternoon, but the arrival of sufficient moisture will wait until after sunset.

SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/
A mid-level trough will cross the Great Lakes tonight and swing across southwest PA on Monday. The lower levels will saturate to some degree ahead of this shortwave, and low-level flow will veer to a more favorable northwesterly direction. This is what will fuel a blossoming of showers that will change from rain to snow this evening, with virtually all precipitation in the CWA in the form of snow from the overnight hours into Monday. Peak coverage of snow showers will likely occur between midnight and sunrise Monday, and be most favored north and east of Pittsburgh with lake influence and upslope flow being factors. Wind gusts will also pick up late tonight into Monday as the surface pressure gradient tightens. Snow shower coverage will become more isolated with time through Monday as the shortwave trough axis crosses and as inversion heights start to lower. Snow is currently expected to cease by 00Z Tuesday.

Accumulation should be muted in many cases by only partial penetration of the saturated sub-inversion layer into the dendritic growth zone, with cloud tops bottoming out around -13C to -15C. The warm ground will also hinder accumulation, especially in areas where the snow remains generally light. The main exception area will be the Laurel Highlands into the northern West Virginia ridges. Here, the changeover to snow will happen during the early evening, and surface temperatures in the higher elevations will drop faster. The far southeastern corner of the CWA, particularly eastern Tucker County, may even get skimmed by a very brief period of upper jet coupling that could enhance lift and lead to heavier snow rates for a few hours.
This, in addition to the elevation/upslope factors, leads to an expectation of 5 to 7 inches of snow for the event in this lone forecast zone. Grand ensemble probabilities of 6 inches or more have increased slightly to 40 to 50 percent for a decent portion of this zone. Think that this might be slightly underdone, and as a result, the existing advisory has been upgraded to a Winter Storm Warning. Confidence in advisory-level snow has also increased in the bordering zones of western Tucker and eastern Preston, where a new Winter Weather Advisory has been hoisted.
The Laurel Highland ridge zones of Fayette and Westmoreland also stand to receive 1 to 3 inches, perhaps a bit higher on the highest peaks such as near Seven Springs. This area will need to be monitored for a possible Advisory if confidence increases later today. Lake enhancement may lead to 1 to 2 inches in the far northern portions of Mercer and Fayette, as well as Forest County. An inch or less is expected elsewhere given the previously mentioned limiting factors.

Ridging over the Central Appalachians will likely clear the sky Monday night. Went a bit lower than NBM suggestion for low temps due to the cold advection, with mins generally in the 20 to 25 ranges, with teens on the highest ridges. If gusty winds continue, apparent temperatures could drop into zero to 10 above range in the higher terrain.

LONG TERM /TUESDAY THROUGH SATURDAY/
High pressure to our south and quasi-zonal flow will provide dry weather and temperatures moderating back to climatology on Tuesday.
A frontal passage Tuesday night/Wednesday appears to have too little moisture for precipitation, but could knock around 5 degrees off daytime highs as compared to the previous day.

Ridging then takes hold over the eastern CONUS during the Thursday/Friday period, continuing the dry weather trend. Rising heights will contribute to warming temperatures, perhaps to above- normal levels by Friday. Will continue with a dry forecast for Saturday for now, but increasing moisture from the south may put that forecast in jeopardy.

AVIATION /12Z SUNDAY THROUGH THURSDAY/
A cold front has pushes through much of the area to start the TAF period, with all but the easternmost terminals (DUJ/LBE/MGW)
reporting west or northwest winds. Expect the front to reach these remaining terminals within the first couple hours of the period. The entire area will see MVFR/IFR ceilings through much of today. Terminals west of a FKL-PIT-HLG line will see a break in showers this afternoon and slight improvement to widespread MVFR, while areas east of this line over the higher terrain likely remain socked in with rain and IFR ceilings. For the most part, showers have been light enough to keep reductions in visibility at or above 6 miles. However, cannot rule out some heavier showers in the higher terrain over northern WV and southern PA (mainly around and east of MGW/LBE) capable of dropping visibilities to 3-5 miles at times.

Showers return to the entire area this evening and transition to snow as temperatures begin to drop, with the best chances for impacts to local terminals being along/north of I-80 and over the high terrain east of PIT/MGW. Meanwhile, northwest winds strengthen tonight into Monday morning, with gusts to 20 knots in the lowlands and 30 knots closer to the ridges.
Ceilings continue to hold steady at MVFR (locally IFR) levels overnight and into Monday before finally beginning to improve just beyond this TAF period.


OUTLOOK
Restrictions in snow and rain into Monday, particularly at terminals north of I-80 and close to the mountains. A return to VFR is expected late Monday and should persist through much of next week with building high pressure.

PBZ WATCHES/WARNINGS/ADVISORIES
PA...None.
OH...None.
WV...Winter Weather Advisory from 7 PM this evening to 1 PM EST Monday for WVZ512-513.
Winter Storm Warning from 7 PM this evening to 1 PM EST Monday for WVZ514.

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