Area Forecast Discussion
Issued by NWS State College, PA

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410 FXUS61 KCTP 210353 AFDCTP Area Forecast Discussion National Weather Service State College PA 1053 PM EST Mon Jan 20 2020 .SYNOPSIS... Northwest flow aloft and a large area of surface high pressure building southeast from the Upper Mississippi Valley will bring a lengthy string of dry days this week. Temperatures will start out below normal before moderating back to normal on Wednesday, then above normal to close out the work week. A slow-moving area of low pressure will bring the potential for snow or mixed precipitation this weekend. && .NEAR TERM /UNTIL 8 AM TUESDAY MORNING/... Clouds back into the NW and have caused the temps to rise again there. BFD got down to 6 F before the clouds rolled in. This is as expected. As is the mid teens at SEG and THV already. A few flurries are falling at JHW, OLE, and likely in nrn Warren/McKean Cos by now, too. Only a dusting of an accumulation is expected in the NW overnight. All is well on track. Prev... Temps dropping. Sky clear for all but the far SW and far NW. Still some wind to keep things mixed up. A weak sfc trough approaching from lower Ontario will create an increase in clouds over the NW third/half of the area tonight. There could be a few flurries, but opted to keep PoPs out of the forecast. The clouds may also bump the temps back up over the NW after an initial dip early tonight. Went below guidance for mins in the east where wind should continue to calm down. The usual cold spots in the valleys will get quite a bit colder than the cities and hill tops. Prev... GOES-16 visible channel shows inversion heights have suppressed shallow stratus bands over the eastern third of Lake Erie, leaving downwind locations of the NW Mountains in full sunshine this afternoon. Only parts of the Laurel Highlands are still seeing any locally enhanced stratus from overlake flow tracing from Lakes Huron and Erie. Boundary layer flow maintains similar trajectory tonight while slackening as high pressure builds across the Ohio Valley. A few clouds will likely drift back over the west and northwest tonight from time to time and over the Laurel Highlands, but the remainder of central PA is expected to remain mostly clear to clear. With decreasing wind and snow cover, tonight will be quite cold throughout with mins ranging from the single digits above zero over much of northern and central PA to 10 to 15 over the south. && .SHORT TERM /8 AM TUESDAY MORNING THROUGH THURSDAY NIGHT/... Upper ridge and elongated surface high will build southeast on Tuesday continuing fair and cold conditions. Highs will be a few degrees higher on Tuesday, ranging from the mid to upper 20s north to the lower 30s southeast. Fair weather and moderating temperatures are expected Wed and Thu, as high pressure settles along the east coast. && .LONG TERM /FRIDAY THROUGH MONDAY/... Focus in the long term remains on the potential winter storm this weekend. All medium range guidance shows a similar scenario playing out, with an upper low lifting northeast from the Miss Valley and high pressure parked north of New England. The resulting anomalous southeasterly low level jet and plume of Atlantic moisture overrunning a dome of cold/stable air east of the Appalachians justifies increasing POPs Saturday. The latest GEFS mean qpf ranges from 0.6 to 1 inch across the forecast area by Saturday evening. Despite the high confidence of significant precipitation, plenty of uncertainty remains with regard to ptypes across the area. Primary surface low is progged to weaken over the Ohio Valley Saturday, as secondary low deepens and tracks up the Mid Atlantic coast in classic Miller B fashion. Quicker development of the coastal low would imply low level winds backing from SE to NE, supplying cold air at low levels during the storm on Saturday. This would mean more wintry precip and less rain. Quicker development of the coastal low could also translate to better frontogenetical forcing/banding on the NW side of the developing low, which would translate to heavier precip and some dynamic cooling. It will be a couple of days before we have these answers. As always, it will be interesting to see how the hi-res guidance handles these features as the event comes in range. Based on the latest ECMWF ensemble 850temps and GEFS plumes, current forecast is for a wintry mix across much of the forecast area Friday night into Saturday, with primarily rain over the Lower Susq Valley and the best chance of significant snow over the northern counties. A deep, moist northwest flow associated with deformation band should result in lingering light upslope snow/rain showers Sat night into part of Monday, primarily over the Allegheny Plateau. Do not expect any contribution from the lakes, as the air mass behind departing storm looks too mild to support lake effect. && .AVIATION /04Z TUESDAY THROUGH SATURDAY/... Widespread VFR through tonight. MVFR conditions resume after midnight Tuesday morning at BFD and JST as low cigs redevelop. IFR conditions will be possible starting early Friday morning at BFD with snow showers. .Outlook... Tue...Mainly dry, but still a chance of snow showers across the northwest. Wed-Thu...Mainly dry. Fri-Sat...Snow/wintry mix Fri night and Saturday. Restrictions psbl. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir/Lambert NEAR TERM...Dangelo/DeVoir SHORT TERM...DeVoir/Lambert LONG TERM...Fitzgerald/Colbert AVIATION...DeVoir/Banghoff

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