Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 171309 AFDCTP Area Forecast Discussion National Weather Service State College PA 809 AM EST Wed Jan 17 2018 .SYNOPSIS... The trough of surface low pressure near the Mid Atlantic Coast and slow-moving upper level disturbance over Pennsylvania that brought us our recent bought of moderate to heavy snow accumulations, will slide off the East Coast late this morning. Surface high pressure will build into the region this afternoon through Thursday, bringing clearing skies but cold temperatures. Temperatures will moderate to near normal Friday, then climb into the 40s or about 10 degrees above normal over the upcoming weekend with mainly dry weather continuing. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Steady light snow is quickly diminishing to just flurries across our SE zones and we`ll see a steady improving trend there late this morning and this afternoon. The Winter Weather Advisory across the Lower-Mid Susq Valley and Wrn Poconos expired at 12Z. Little or no additional accumulation will occur, but roads will be slick for at least a few-svrl more hours as temps stay well below freezing. Strong, deep-layer subsidence beneath the thermally direct, Left Entrance region of a swrly 130-140kt upper jet, will combine with a light westerly surface flow of much drier air to bring a sharp line of clearing and several hours of sunny skies to the Central Mtns late this morning into this afternoon. Overcast skies in the east will see cloud bases rise from between 2-4kft agl early today...to 18-20 kft agl by noon with some sunshine later this afternoon. Over the western high terrain, variable cloudiness in the form of shallow, upslope strato cu will bring some flurries near and to the west of the Route 219 corridor as temps of -12 to -18C within this cloud layer reside smack in the middle of the DGZ. A light additional coating of snow will occur at most on the western slopes and ridges of the Laurels and NW Mtns today. NBM/Superblend numbers indicate readings by dawn ranging from the lower single digits over the Alleghenies, to the low 20s over the Lower Susq Valley. Ensemble mean 925mb temps of around -13C support highs this afternoon ranging from the mid teens across the Western Mountains, to the mid 20s over the Susq Valley. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Periods of strato cu and brief flurries will linger across The Western Mtns early tonight, with just some sct-bkn alto cu clouds afterward across much of the CWA. Low temps tonight will vary from near 5 above zero across the perennial cold spots of the NW Mtns, to the low to mid teens across the Southern Valleys of PA. Mostly sunny skies will occur Thursday with temperatures rebounding to near or slightly below normal. Westerly sfc flow will freshen during this short term period, and will gust between 20-25 mph tonight (mainly over the western mtns). Gust potential will increase to 30 to 35 mph Thursday across Central and Western parts of the CWA as high pressure builds over the Lower Ohio Valley and SE States, while a strong North- South pressure gradient resides across the Midwest, Great Lakes Region, and Upper Ohio Valley into PA. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... The medium range will feature a fairly long period of dry- tranquil weather with soon to moderating temperatures. A milder westerly flow will develop to close out the week as a surface high slides along the Gulf coast toward the SERN US. By Friday...WSW flow will push daytime highs above freezing over most of the forecast area, and temperatures are expected to continue to creep upward into the weekend. Temperatures by the weekend will be well above normal under the building eastern ridge. The next chance for precipitation looks to not be until later Saturday into the overnight with a surge of warm advection that is made to develop with the approach a warm front that should slide up to our west into NY state. The chance of showers favoring mainly western areas will continue through Sunday. There is remarkably good agreement at this range in dragging a significant cold front through the area Monday afternoon or evening. The GEFS takes the best PWAT anomaly up through the eastern lakes mainly west of the CWA and right now shows a generally light-moderate rain event. Of course any kind of warmup accompanied by rain will create ice-jam and flooding concerns so that looks to be the next big threat moving forward. && .AVIATION /13Z WEDNESDAY THROUGH SUNDAY/... Snow just about over for eastern portions of CWA (just ended at KMDT) as low responsible for it continues to drift to the NE away from central PA. Restrictions will end over the Lower Susq by mid morning as conditions improve to VFR with NW downslope flow taking over. Already VFR over central/southern mountains in chilly NW flow - but a short period of ceiling restrictions possible mid morning as trough slides through. This trough will keep restrictions in the western/northern higher terrain much of the day before seeing improvement there tonight. Winds will become breezy, esp in the SE with gusts increasing to around 20 mph. High pressure builds in tonight, bringing a mainly VFR night to the region. Cig restrictions may still be lingering into the evening at KJST though, with a breezy night in store there as well. Outlook... Thu...Mainly VFR. Breezy. Fri-Sun...Mainly VFR. && .HYDROLOGY... The threat of ice jamming is diminishing. Dry and colder weather into mid week will form additional ice as stream flows and open channels decrease. Another warm up is expected by the end of the week into the weekend with rain to accompany a frontal system early next week. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...La Corte/Lambert AVIATION...RXR HYDROLOGY...

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