Scientific Forecaster Discussion
000 FXUS61 KPBZ 061534 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1034 AM EST Fri Dec 6 2019 .SYNOPSIS... Light rain showers and drizzle will be possible today ahead of an advancing cold front. High pressure is expected to bring dry and quiet weather this weekend. && .NEAR TERM /THROUGH TONIGHT/... 1030am update...Added sprinkle/drizzle wording areawide this morning as moisture increases ahead of the advancing shortwave trough, but struggles to overcome drier air near the sfc. Otherwise, the forecast remains on track. Previous Discussion... Increasing moisture will increase chances for drizzle and light rain showers through this afternoon ahead of a passing shortwave trough. Dry air near the sfc will initially limit areas that see precip reaching the ground, but continued top-down moistening and additional lift with the arrival of the sfc cold front will allow for more developed rain showers. Timing of the sfc cold front plus upslope flow means light accumulating precip will favor areas south of I-70 and along the eastern ridges. Passage of the shortwave trough and cold front will create a brief period of NW-erly flow, that combined with cooler air, could create light wintry mix showers north of I-80 and at elevations above 2,000ft. Otherwise, building sfc high pressure will bring dry conditions to the region overnight. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Near-neutral temperature advection will maintain below average temperature given quasi-zonal flow aloft through Saturday. Clouds will gradually clear late Saturday afternoon, once drier advances into the region. A pattern shift is then anticipated Sunday as a Hudson Bay low deepens, returning swly flow and warm advection aloft. Above average temperature is expected Sunday, with surface high pressure prevailing. && .LONG TERM /MONDAY THROUGH THURSDAY/... Stratiform rain chances increase Monday as a series of shortwaves impact the region on the van of the deepening Hudson Bay low and associated central Plains trough. Deep moisture transport is expected given strong jet support, with PWAT values in exceedance of the climatological 90th percentile. This should support widespread rain Monday into Tuesday. Long term model blends agree on the arrival of an arctic front by Tuesday / Wednesday, changing rain over to snow given cold advection in nwly flow behind the frontal passage. Wednesday high temperature should top out 15 to 20 degrees below average. Some moderation, albeit limited, is expected Thursday as flow aloft becomes quasi- zonal. && .AVIATION /16Z FRIDAY THROUGH TUESDAY/... Low-level wind shear likely this morning ahead of an approaching cold front with frontal passage over the course of the afternoon. Scattered showers will be possible but given limited moisture should not bring widespread restrictions other than an MVFR cigs. .Outlook... More restrictions are likely early next week with the next disturbance. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None.