Scientific Forecaster Discussion
000 FXUS61 KPBZ 121720 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1220 PM EST Thu Dec 12 2019 .SYNOPSIS... Dry and relatively warmer weather will continue today into Friday before a low pressure system returns rain to the area Friday night and Saturday. && .NEAR TERM /THROUGH TONIGHT/... At 650 AM, made some minor updates to sky cover and hourly temperatures. Generally quasi-zonal flow aloft will bring patches of high clouds across the area through the afternoon, with plenty of sunshine still figured. Previous discussion... Strong, southerly return flow will begin today with eastward progression of the sfc high and a digging trough across the upper Midwest. WAA will drive temperatures up nearly 10 degrees higher than Wednesday, though still a couple degrees below seasonal average. Otherwise, quiet and mostly sunny(!) weather continues. && .SHORT TERM /FRIDAY THROUGH SATURDAY/... Continued warm, moist advection will slowly saturate the column overnight in advance of a mid-level shortwave trough, resulting in increasing cloud cover once again this evening. A warmer airmass along with the effects of cloud cover will result in minimum temperatures Friday morning around 10 degrees warmer than those of this morning and close to seasonal norms. The aforementioned mid-level wave will force weak cyclogenesis across the Southeast US tonight, resulting in a sfc wave lifting north as an eventual coastal low on Friday. While the low will remain to our east while sliding up the coast, warm/moist air will overrun a cold sfc layer in the ridges Friday late morning into the afternoon. The complicated thermal profile will be favorable for freezing rain and possible sleet mixing in with rain and snow in portions of the higher elevations until the sfc warms to above freezing. Additional freezing rain will be possible Friday evening as locations in the ridges drop back below freezing with warm air aloft. Some ice accumulation will be possible, especially across Garrett County, MD, and headlines may be needed. Outside of freezing rain, a decent rainfall event is likely with this system as QPF values from 0.5 to 1 inch are expected over much of the forecast area through the weekend. Warm advection will push afternoon temperatures on Friday and Saturday into the 40s. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Rain will transition to a mix of rain/snow or all snow Saturday night into Sunday morning as temperatures cool with cold advection in the wake of the low. At this time, do not expect much in the way of snow accumulation outside of light amounts in the ridges and higher elevations given lack of deep moisture in the dendritic growth zone. Continued westerly flow will also be unfavorable for typical, post- frontal upslope snow. Considerable model uncertainty continues with respect to the potential winter system Monday into Tuesday. Latest EC keeps the weak, crossing low to our south, keeping most of the CWA in the cold sector and in play for winter weather for much of the event. GFS, however, pushes a more robust low to our west and north across Lake Erie, limiting winter p-types to brief overrunning with the warm front. Given the uncertainty at this time, the winter weather threat for snow and ice will need to be monitored over the next several days. Expect temperatures to remain near seasonal average Sunday through Tuesday, depending on the track of the sfc low, with a cool down on Wednesday. && .AVIATION /17Z THURSDAY THROUGH MONDAY/... VFR conditions are expected through the forecast period. High clouds are expected through most of tonight, with lowering/thickening clouds after 12Z Friday as moisture increases ahead of an approaching shortwave. Light precipitation will arrive after that time as well, with freezing rain possible along the ridges and a rain/snow mix to the west. .Outlook... Restrictions are likely this weekend with crossing low pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None.