Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 162246 AFDCTP Area Forecast Discussion National Weather Service State College PA 546 PM EST Sat Dec 16 2017 .SYNOPSIS... High pressure is moving in for tonight and last into Sunday. A weakening wave of low pressure will move in from the midwest late Sunday. Scattered snow showers will be in store for the west during first part of the week. Fast west to east flow aloft will keep the weather unsettled. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Clouds will likely hold on all night in the NErn half to 1/3rd of the the area with warm advection and lift just above the blyr. However, the moisture will be decreasing through the evening, and the light snow should dwindle to flurries by midnight and little should be left after that. Mins are tricky with clearing in the south but the light SW wind will try to keep temps up a little. Locations to the east of the Susq will likely fall the hardest with snow on the ground. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... Clouds in the NE half/third should begin to break up, but just in time for a new batch of warm advection to ride in from the west later in the day. So, there will likely be an increase in clouds over the SW, and a waffle from clouds to no clouds and back again in the central/NE. We are expecting some light precip to break out in the SW/SC counties by nightfall. The temps will get into the 40s in the south with sun. without much sun in the NE, it will likely stay below 35F. The low pressure over the mid-MS valley will fall apart as it goes into the OH valley and a loss of moisture will kill much of the precip as the feature fills over us and moves eastward Sun night. The clouds will likely hang low and thick, keeping temps up. Many places should stay above freezing. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... Fast westerly zonal flow will turn a bit more SW by Friday as a trough digs over the upper Plains. A western trough kicks a strong shortwave out across the Plains Sunday into Monday. The associated low center will move northeast across the Great Lakes staying to our north. This system will drag in some warmer air in southwest flow ahead of it. However, we may be cold air dammed near the surface so the +1 to -2C air at 850 hPa may not translate to a warm boundary layer. The warm advection should bring snow and snow to rain in the south but QPF amounts are light. Will have to watch for potential for some ice also Sunday night. Then through much of the week, we move to fast moving pattern of weak shortwaves and chances for precipitation (mainly over the northern mountains) through the week. As a northern stream wave zips by to our north by Monday night, it will bring cold air back into the region Tuesday into Wednesday. The northwest flow triggers snow in relatively high POPS in NW PA due to LES. This cold surge should be relatively fleeting and high pressure and a potential surge of relatively warmer air follows Thursday. The warm advection and approaching cold front will likely produce increased potential for snow/ice in the west Thursday night into early Friday. As precip works in on Friday, precipitation looks to transition through mixed to light rain. Temps could fall below guidance over the east Thu night if skies remain clear as exiting surface high pressure will leave a dry airmass in place. A strong frontal boundary will likely push another surge of cold air into the region Friday into Saturday as the eastern long wave trough tries to re-establish itself. GFS and ECMWF diverge by this time, with the EC moving surface low slower and thus forecasting higher pops than GFS. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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Radar trends continue to show weakening of lake effect streamers across northern Pennsylvania early this evening. As winds continue to slacken overnight, expect snow shower activity to come to an end in most areas by 02z-04z. Satellite shows stark contrast between nearly overcast skies north of a KDUJ to KLNS line, with nearly clear skies south of this line. With slackening NW flow, would expect clouds to thin and break up over eastern areas this evening, However, given weak frontal boundary in place across northern Pennsylvania, and little push of wind overnight, stratus will likely hang tough overnight across the northern mountains. Warm advection ahead of the next system will bring increasing clouds from the Southwest Sunday, with a chance of precipitation by late in the day in the SW. Outlook... Sun...Lingering MVFR to IFR lingering in the western and northern mountains, otherwise VFR elsewhere. Mon...Mainly VFR. Spotty SHSN poss W. Tue...Mainly VFR, but possible restrictions in the western and northern mountains in snow showers. Wed-Thu...No sig wx.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...RXR AVIATION...Jung/Dangelo

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