Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 150017 AFDCTP Area Forecast Discussion National Weather Service State College PA 717 PM EST Thu Dec 14 2017 .SYNOPSIS... A weak ridge of high pressure will slide across the region tonight with cold, but mainly dry conditions. Another clipper will move north of the region overnight Friday and Saturday morning followed by high pressure and a brief moderating trend in the temperature Sunday. A series of cold fronts will move across the area late Sunday into Wednesday. Windy and colder temperatures will follow. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Radar showing a few light lake effect snow showers/flurries across the Warren/Mckean counties early this evening. However, boundary layer flow is progged to back to the southwest shortly, shifting remaining lake effect activity north of the border. Otherwise, fair and chilly conditions overnight, as surface high drifts over the state. Some increasing high clouds expected overnight associated with waa aloft ahead of approaching shortwave. However, light winds and snow cover should allow readings to drop into the single digits north to upper teens south. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... After a cold start temperatures will recover only to highs near 20 in the north to around freezing in the extreme southeast. Clouds and snow showers will be most likely late in the day over the Allegheny Plateau, as a shortwave turns the flow more NWLY and brings a chance of Lake Effect back into the areas normally affected this time of year. Developing low off the Mid Atlantic coast could potentially graze the extreme southeast corner of the forecast area during the afternoon, so have included low POPs down there for a period of light snow. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... The period starts out with below normal 500 hPa heights and below normal 850 hPa temperatures. The heights and temperatures rise to above normal values over the northeastern United States Sunday as a strong ridge retrogrades to our south. The really warm air should stay to our southeast. The heights and temperatures settle back toward normal Tuesday and Wednesday at 500 hPa and 850 hPa respectively. Temperatures may rebound Thursday ahead of another frontal system. Overall with the strong ridge to our southeast the fronts do not get too far south. Saturday we should still be in the cold air with some LES based snow activity in the northwest. As the high retreats to our east temperatures should begin to rebound and the snow showers in the northwest diminish. Sunday into Monday a strong shortwave to our north will help bring in warmer air. 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 low and EFS based POPS are not very high in central and southern areas. As this northern stream wave zips by to our north it should drag 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 warmer air in the NAEFS/GEFS. This suggests relatively warmer on Thursday. The Warm advection and approaching cold front will likely produce increased potential for snow in NW Thursday into Friday. Farther south any precipitation would likely be mixed or rain. A strong frontal boundary will likely push another surge of cold air into the region Friday into Saturday. At this time and recent GEFS/CMCE and combined NAEFS runs keep the strong ridge suppressed to our south. This keeps the warm air from getting here. This keeps us relatively dry with all the significant QPF events suppressed to our south. There is considerable spread in the ensemble members. And we have seen run-to-run variations in the solutions with the strong southwest Atlantic ridge. The NAEFS deeps reforming vortex over east-central Canada and maintains the sharp ridge over northwestern North America. This seems to keep us in or on the edge of cold air intrusions. Thus so far single model runs of big warm ups appear to disappear in the ensembles. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... * Cloud/Ceiling info will be missing at KBFD until new part can be installed * All Central Pennsylvania airfields now reporting VFR conditions, although appears there are still some patchy MVFR ceilings as depicted on satellite across the northern mountains. Overnight will be clear to partly cloudy and cold with some MVFR ceilings expected to move back into the higher elevation terminals of the west and north. The chance of snow showers will be on the increase Friday, mainly over the north. Outlook... Fri...MVFR with snow showers north and west mountains, mainly VFR elsewhere. Sat...Scattered snow showers and local restrictions NW/Laurels. Sun-Mon...Mainly VFR. Tue...mainly VFR, but possible restrictions in the western and northern mountains in snow showers. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald/La Corte LONG TERM...Grumm AVIATION...Jung

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