Area Forecast Discussion
Issued by NWS State College, PA

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893 FXUS61 KCTP 220048 AFDCTP Area Forecast Discussion National Weather Service State College PA 748 PM EST Sat Jan 21 2017 .SYNOPSIS... Unseasonably mild weather will continue through the weekend. A complex and dynamic storm system will bring the potential for heavy rain, accumulating snow and strong winds to portions of Central PA on Monday. The mild conditions will last into the middle of next week before a pattern change brings colder air and more seasonable temperatures to close out the month. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Fog rapidly lowering/redeveloping this evening in areas where inversion hung strong throughout the day. Already seeing M1/4sm visibility pockets and the next few hours should see many more with some very difficult travel at a time of day that usually does not see dense fog. Issued Dense Fog Advisory for all most areas east of the Allegheny Front until 03z...as mid to high clouds spreading ENE with approaching upper trof should diminish the extent and severity of fog by late evening...we think. Otherwise, cloudy and unseasonably mild overnight with minimum temperatures +20-30 degrees above normal for late January. There could be some pockets of light rain/drizzle but generally kept POPs below 20 percent. Rainfall associated with surface low tracking northeast from GA/AL is fcst by the models to stay southeast of the area. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Closed mid-level low tracks from the ARKLATEX to western VA/NC by 23/12z. Moisture and inflow will increase ahead of the mid- level system and should support rainfall pivoting northward into southern areas by the end of the period. Model QPFs indicate the main rain axis stays to the south of the PA/MD line although placement highly anomalous easterly flow of high PW air into e-w frontal zone has me a bit concerned. One thing of note is an increase in winds over the Lower Susq. valley with gusts over 40 mph possible by daybreak Monday. Temperatures stay very mild and well-above normal for this time of year. && .LONG TERM /MONDAY THROUGH SATURDAY/... All model data tracking closed upper low northeast across Virginia Monday. Continue to maintain 100 pct POPs across the entire region, given the strong upper lvl divergence, anomalous easterly low lvl jet and associated PWATS. Latest GEFS/SREF also both support the 100 POP forecast. Initially, model temp profiles are warm enough everywhere for rain, but dynamic cooling associated with the strongest forcing will likely support a change to snow, at least temporarily, over the higher terrain of central Pa. GEFS/SREF ptypes still strongly favor rain, but based on operational model soundings and colder 12Z ECMWF will maintain mention of snow over the central counties. Best chance of accumulating snow based on soundings is across the northern Mtns, where a few inches of accum appear probable by Mon evening. Uncertainty too high to mention accums further south, but the potential for a few inches of wet snow remains from the Laurel Highlands into the Central Mtns. Another area of concern is the potential for flooding. Target area for the heaviest rain is across the south central part of the state, where orographic forcing at nose of powerful easterly low lvl jet will play a role. Mean QPF from both SREF and GEFS max out around 1.5 inches in this region, while FFG/FFH is around 2 inches. However, locally higher amounts seem probable and are hinted at by the higher resolution NAM, so will mention the possibility of minor flooding in the HWO for this area late Monday. Lastly, Bufkit soundings indicate wgusts in excess of 40kts are possible across southeast Pa, as low lvl jet swings through Monday. Per coordination with LWX/PHI, will hold off on an advisory pending increased confidence from later models. Precip will lift out of the region Monday night, as sfc low passes off the NJ coast. Upper ridging will build into the region later Tuesday into early Wed, bringing fair and mild wx. A shortwave passing across the eastern Grt Lks will push a cold front thru Pa late Wednesday, accompanied by sct showers, then a shift toward colder wx is progged by all med range guidance for the Thu-Sat time frame, as a deepening upper lvl trough forms over eastern North America. Best chance of precip will be in the form of lake effect snow showers across the NW Mtns during this time, with dry weather likely elsewhere. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/...
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Widespread IFR-LIFR continue over much of central and eastern airfields early this evening. Areas in the western mountains have mixed into the warm air, and continue to experience VFR conditions. Expect IFR-LIFR conditions to persist over the region overnight. In those areas that are clear and VFR, also expecting fog to redevelop overnight with moist surface conditions and light winds. Approaching shortwave and associated light showers may bring a slight improvement to conditions after 03z...but generally a low cig/vsby night in store for most of the region. Outlook... Sun...IFR-LIFR early, some slight improvement to MVFR/IFR during the day. Rain spreads from south-north Sunday afternoon and evening. Mon...Rain/low CIGs likely. Tue...AM rain/snow and low CIGs possible. Wed...Reduced CIGs/showers possible NW. Thu...MVFR/IFR in rain/snow showers mainly west.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 10 PM EST this evening for PAZ012-018- 019-025>028-034>037-041-042-045-046-049>053-056>059-063>066. && $$ SYNOPSIS...Steinbugl NEAR TERM...DeVoir/Steinbugl SHORT TERM...Steinbugl LONG TERM...Fitzgerald AVIATION...Jung

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