Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 140146 AFDCTP Area Forecast Discussion National Weather Service State College PA 846 PM EST Mon Nov 13 2017 .SYNOPSIS...
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High pressure will build into the area from the Ohio Valley and last into Wednesday. Shallow, moist upslope flow ahead of this high will produce areas of drizzle across the northern and western mountains early tonight, with patchy freezing drizzle possible late tonight across the highest terrain in the north and west. One cold front will move through Wednesday night and then another over the weekend with high pressure in between the two.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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High pressure will be slowly pushing into the area from the west late tonight and Tuesday. Shallow, cold and moist upslope flow (with cloud layer temps in the -1 to -6C thermal ribbon, and deep dry air aloft) will support super-cooled water droplets. As temps in that part of the state dip a few to svrl deg F from their current 01Z Tuesday readingsin the 34F to 37F range, there is the potential for some patchy freezing drizzle Late tonight through shortly after sunrise Tuesday. There are some mid level clouds moving into far Wrn PA with IR imagery indicating temps in the favorable thermal ribbon for dendritic growth (-13 to -18C), so it`s not out of the question to see some wet snowflakes produced with the help of this seeder-feeder deck, especially accompanying the fleeting/stronger radar returns (one of which is heading SE across Clearfield County ATTM). The cloud cover is the problematic part of the forecast, since precip type hinges on it and the ultimate effect on sfc temps. The low clouds will scatter some warmth back to the earth, and this could keep the sfcs just a little milder than freezing. Therefore, refrained from hoisting any flags pertaining to the patchy light freezing drizzle, but rather mentioned it in the Gridded forecast database, ZFOCTP and Hazardous Weather Outlook (HWOCTP). SE of a KAOO to KUNV and KIPT line to the I-81 corridor. skies will be partly to mostly cloudy with mainly dry conditions. Skies acrs the Lower Susq Region will be clear to partly cloudy until very late tonight when periods of BKN sky cover may develop. Min temps will vary from near 30F across the northern and western mtns, to the lower and middle 30s elsewhere.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... The axis of the big sfc high floats over the area and the thermal trough aloft begrudgingly gives up and lifts to the NE on Tuesday. Clouds over the NW half/two-thirds of the area take a long time to break up - maybe not until close to sunset in the north-central mtns. Temps should be close to 50F in the SE where the most sun shines through, but still only in the u30s to near 40F in the higher elevations/nrn mtns. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... High pressure over the region Tue night retreats to the NE on Wed as a low pressure area track east across the Great Lakes. Warm front lifting ahead of the low will bring chance for showers to western sections early Wed with higher likelihood of showers Wed night into Thu as the low tracks north of PA. Colder air filtering in may bring brief shot of snow showers to mainly NW mtns on Thu. Ridge of high pressure slides through Thu night through Fri. This will be followed by a deepening storm system that will move into the upper Great Lakes later Friday into Saturday - with rain developing Fri night and persisting as a cold front swings through on Saturday (earlier in the day if you are a fan of the GFS, later with the ECMWF). Rain ahead of this system will transition to lake effect snow showers by Saturday evening/night and Sunday with arctic air sweeping into the state. NW flow will then keep clouds and snow showers in the forecast for NW portions of CWA Mon into Tue. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... High pressure building in from the Great Lakes will bring fair weather and light wind to the eastern half of Pa tonight. However, a shallow layer of moisture, combined with light upsloping flow, will likely yield IFR cigs and patchy drizzle/fzdz overnight at KBFD and possible IFR cigs further south at KJST later tonight. The other area of concern will be across the Lower Susq Valley, where radiational cooling under partly cloudy skies is likely to promote areas of fog. Based on early evening dewpoint depressions and near term model data, believe KLNS is most likely (around 50 percent) to experience a period of IFR vsbys overnight, while odds at KMDT and KIPT are closer to 20-30 percent. Any reductions in the form of low cigs across the western mountains, or fog in the Susq Valley, should give way to improving conditions by midday, as low level moisture mixes out. Model soundings and SREF probability charts indicate widespread VFR conditions are likely by late afternoon with the possible exception of KBFD, where MVFR cigs may linger. East/Southeasterly flow begins Tues night and may cause some low clouds over the central mtns. But, VFR is more likely. Any low clouds will melt away Wed AM, and most of the day will a fine day to fly. A cold front nears and will pass through Wed night. Low cigs and rain showers likely NW and poss SE. Sct SHSN poss NW Thurs behind the front. Outlook... Wed...Patchy AM fog possible eastern Pa. Evening showers/low cigs possible KBFD. Thu...AM low cigs/SHRA possible KBFD/KJST. Fri...No sig wx expected. Sat...Rain/low cigs possible, esp KBFD. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo/Lambert NEAR TERM...Dangelo/Lambert SHORT TERM...Dangelo LONG TERM...RXR AVIATION...Fitzgerald

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