171 FXUS61 KCTP 211443 AFDCTP Area Forecast Discussion National Weather Service State College PA 1043 AM EDT Sat Mar 21 2020 .SYNOPSIS... The first weekend of spring will be dry and relatively cool with temperatures below average. Odds are increasing for a late season snowfall across parts of the area late Sunday night into early Monday, with minor to moderate accumulations most likely over the interior north central mountains. Another brief dry spell is expected Monday night into Tuesday before the next round of precipitation for midweek. Temperatures will trend warmer and climb back above average into the second half of next week. && .NEAR TERM /THROUGH TONIGHT/... 1035 am update... The current forecast is in good shape, so only cosmetic tweaks are required at this time. What a change 24 hours makes, as the resident air mass covering the Commonwealth right now features temperatures 30+ degrees lower than yesterday. Highs this afternoon will feature highs ranging from the mid-upper 30s in the northern mountains, to the 45-50 range in the Middle and Lower Susquehanna Valleys. As for cloud cover, the mass of stratocumulus clouds is gradually shrinking back from the north and east late this morning, with cloudy skies still seen in areas generally north of I-80 and west of I-99. Given a shallow moist layer, as seen on morning soundings at Pittsburgh and Buffalo, and also strong dry air advection foreseen this afternoon, we're still anticipating a steady clearing trend. Previous discussion... Spring will go from fast-forward to pause/rewind this weekend with noticeably cooler temperatures expected. The chilly airmass is being directed into the area courtesy of 1040+mb Canadian high pressure migrating east from the Upper Great Lakes into southern Quebec by tonight. Highs in the mid 30s in the northwest mtns to around 50F in the lower Susq Valley will run -5 to -15 degrees below average with a 24hr change between -20 to -30 degrees. Expect clouds this morning to gradually give way to increasing sunshine by the afternoon. Clear skies tonight with lows in the teens and 20s. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... Morning sunshine will mix with and eventually fade behind increasing cloud cover during the afternoon and evening. Highs will be a tad warmer than Saturday in the low 40s to around 50F. Trended dewpoints lower than guidance given favorable synoptic setup. This results in min RH as low as 15-20 percent over the northeast zones - however recent rains and light winds will preclude fire wx risk. The aforementioned high pressure system will drift across northern New England to a center position over Nova Scotia at 12Z Monday. Models show a cold wedge pattern developing to the south of the strong high along the eastern slopes of the Appalachians. This pattern will set the stage for a potential late season snowfall across parts of CPA Sunday night into early Monday. The first shot of warm advection precip (rain/snow) should arrive between 00-06Z Monday as mid level shortwave moves into the Ohio Valley and sfc low weakens over WV. Expect an uptick in QPF in the 06 to 18Z Monday period as secondary sfc low develops near the VA Tidewater/southern Delmarva region and taps into anomalous PW plume off the NC coast via strengthening east/southeast low level flow. Increasing/heavier precip rates along with wet bulb effects should support sufficient column cooling to trend thermal profiles/ptype toward wet snow across most areas to the northwest of the I-81/78 corridor. Continued to utilize a blend of NBM/WPC for 6hr snowfall with manual adjustments to emphasize elevation dependence. Time of day (nighttime and early in the morning) is a key factor that is bullish for accumulating snow with some slippery travel possible especially at higher elevations. Latest snowfall totals remained pretty consistent with previous forecast: max 2-4" across the highest terrain over the interior north central mtns and slushy 0.5-2" across the rest of the Alleghenies (lower amounts in the valleys 1000-1500ft/higher amounts on the ridges 1500-2000ft). In general, anticipate less snow accum on paved surfaces which could reduce travel impact to some extent. Non paved and elevated surfaces/grassy areas should see the greatest snow accumulation. As the sfc low deepens and lifts to the northeast off the NJ coast, expect WAA and time of day to eventually transition most ptypes to rain Monday afternoon. Rain/snow mix will still be possible across the north central mtns with little to no additional accum in the PM hours. Precip should end Monday night with dry weather expected into Tuesday. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... Next round of precipitation is forecast to arrive Tuesday night and continue during the day on Wednesday. Temperatures should trend warmer mid to late week with lower but non-zero POPs Thursday and Friday. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... Large high pressure area building in from the NW will bring clearing skies today after some morning MVFR restrictions over the NW half. Winds will be from the NNW at around 10 mph, with mixing bringing gusts of 15-20 mph at times. Calm and quiet tonight with widespread VFR conditions as center of high slides by to the north. VFR continues through the day Sunday with morning sunshine slowly fading behind increasing cloud cover during the afternoon and evening. Storm system will bring rain/snow to the region Sun night into Monday, as restrictions develop over the western high terrain Sunday evening deteriorating to widespread IFR conditions by Monday morning. .Outlook... Sun...VFR during the day, with deteriorating conditions at night in rain or snow. Mon...Restrictions in rain and/or snow. Tue...Mainly VFR. Wed...MVFR and IFR conditions with rain likely. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Steinbugl NEAR TERM...Jurewicz/Steinbugl SHORT TERM...Steinbugl LONG TERM...Steinbugl AVIATION...RXR