Scientific Forecaster Discussion
000 FXUS61 KPBZ 131451 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 951 AM EST Fri Dec 13 2019 .SYNOPSIS... Precipitation chances return today with a weak disturbance. Widespread rain is expected tonight and Saturday with crossing low pressure. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Late Morning Update: Due to lingering freezing conditions, the Winter Weather Advisory was expanded further north and west. Icy conditions have been reported in Marion, Preston, and Garrett County. Warm advection should increase temps to above freezing west of the ridges in the next few hours. Eastern Tucker/Garrett's Advisory may need to be extended if temperatures can not make it above freezing due to dynamic cooling. Previous Discussion: Quick update to expand the advisory to Preston and Wrn Tucker counties this morning. Precip advancing NEWD on radar, with temperatures in those areas mainly in the 20s. Expect some warming before precip arrives, though some areas are still expected to be below freezing. Previous...A shortwave embedded in SW flow aloft is progged to track from the Tennessee Valley to Central/Eastern PA today. Mainly slight/low chances for rain are expected across the region, though the higher terrain areas across Wrn MD and Nrn WV are expected to be closer to more favorable upper support and deep layer moisture with precip more likely. With cold air in place at the sfc, and cooling upslope SE flow, a period of light freezing rain is expected across Ern Tucker and Garrett counties. Will maintain the Winter Weather Advisory as is. Some brief, patchy, light freezing rain is possible across Preston county through the Laurel Highlands if precip occurs this morning. If later information indicates higher precip probabilities in these areas, a quick expansion of the advisory may be needed, otherwise not enough confidence in this occurrence to expand the advisory attm. Expect any precip to taper off this afternoon with the passage of the initial wave, with seasonable high temperatures. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... An upper trough is progged to dig across the Central CONUS tonight, crossing the Upper OH Valley region Saturday. A sfc low is expected to develop across the SE CONUS in response to the digging upper trough, tracking along the East Coast over the weekend. Rain should overspread the region tonight and Saturday in warm, moist advection and increasing shortwave support. QPF amounts are expected to range from 1/3 to 3/4 of an inch, so no significant hydro concerns are anticipated. Rain should mix with and eventually change to snow in cold advection after the sfc low tracks by to our E/NE later Saturday and Saturday night, though no significant accumulation is expected with the sfc/boundary layer slowly cooling for most locations, though colder areas across the higher terrain could see a couple of inches. Snow shower chances should continue Sunday both with upslope flow, and a sfc trough across Lake Erie/NW PA. Moisture in the dendritic layer is expected to be limited, precluding any more than a coating of additional accumulation in some areas. Brief shortwave ridging should return dry weather most of Sunday night, though snow chances return late with another approaching Central CONUS trough and associated sfc low. && .LONG TERM /MONDAY THROUGH THURSDAY/... Rain and snow chances increase Monday and Tuesday as the trough and sfc low track across the region. A reinforcing trough should maintain low/slight snow shower chances Wed before low level ridging returns mainly dry weather Thursday. Temperatures should average below seasonable levels through the period. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... MVFR cig restrictions expected today with increasing moisture and a crossing shortwave. Any precipitation will be scattered and light during the day. Further deterioration to IFR or lower is expected tonight through Saturday with more widespread precipitation associated with low pressure moving up the coast. Nearly all analogs show IFR restrictions during this time and 60-80% indicate LIFR restrictions. .Outlook... Restrictions are likely through much of the weekend. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Winter Weather Advisory until 3 PM EST this afternoon for MDZ001. OH...None. PA...Winter Weather Advisory until 11 AM EST this morning for PAZ031- 074>076. WV...Winter Weather Advisory until 11 AM EST this morning for WVZ021- 509>513.