Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 232148 AFDCTP Area Forecast Discussion National Weather Service State College PA 448 PM EST Mon Jan 23 2017 .SYNOPSIS... A strengthening storm will move east of the NJ coast tonight and early Tuesday. High pressure and unseasonably mild conditions will briefly return for midweek before a pattern change brings colder temperatures and lake effect snow to close out the month. && .NEAR TERM /UNTIL 10 PM THIS EVENING/...
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* Major cyclone to affect the region through tonight * Elevation dependent snow storm likely * Several inches of heavy wet snow not out of the question even throughout the Central Valley areas * Strong easterly LLJ 50-65kt/5-7 sigma...translating to wind gusts of 35 to 45 mph near and to the east of the Susquehanna Mainstem * High probability of at least 1" QPF over much of central PA * Explosive dynamic cooling leads to steep mid level lapse rates and a few instances of thunder snow across the region late today and tonight The deep storm that has been responsible for several rounds of severe storms and deadly tornadoes over Dixie the past several days, is now located near Norfolk, VA and will take a track to the northeast up along or just off the NJ coast tonight. Increasing upper diffluence and mid-level frontogenesis across the Mid Atlantic Region will lead to bands of moderate to briefly heavy precip pushing NWWD, then consolidating on a roughly NE/SW axis near the front range of the Alleghenies from near KELM...to KFIG and KUNV...to KAOO and KIDI late today through at least the first half of tonight as the channel anomalously high PWAT air and low-level easterly winds pivots around the north side of the approaching, negative tilt Upper Low. Multi-model and EFS Vertical Thermal Profiles are very close to supporting various types of precip...in various locations as dynamic cooling lowers temps at all layers just below freezing over the Laurel Highlands first late today, then across central and NEPA where varying thickness of the slightly above freezing layer of marine air off the Atlantic will be found. We maintained the basic timing and configuration of the previously posted Winter Storm Warning and Advisories for NCENT PA, but issued a Winter Weather Advisory for the Laurels for late this afternoon through midnight where 2-5 inches is expected in the valleys there, with higher amounts of around 6 inches on the ridge tops AOA 2200 FT MSL. 17-20Z runs of the HRRR shows the first batch of moderate to heavy QPF, in the form of Rain to Sleet, with Laurel Highlands (and shortly afterward the Central PA valley locations) seeing Big, Gloppy Wet Snowflakes. This enhanced area of QPF will be lifting gradually north across the CWA between 21-03Z and becoming concentrated across the northern tier counties of PA later tonight. Elevated...slantwise instability coupled with steepening mid/upr lapse rates moving in from the south should lead to some isolated TSSN (or TS some precip type) through at least early tonight. A second surge of mid/upper level energy pushes NWWD over much of central and eastern PA after midnight and lingers through daybreak in the form of an "elongating" area of "Wraparound" snow/sleet. The main change for later this evening may be the need to extend the Winter Weather Advisory to fill in some of the Central Susq Valley and Central Mtn zones for up to several inches of Wet Snow. Temperatures in most locations of Central and Northern PA will be nearly steady or slowly falling from the mid and upper 30s late today, The rain will mix with, then change to sleet and wet snow during the mid to late afternoon across the higher terrain of central and western PA where temps will be between 32 and 34F. A gradual changeover to sleet and wet snow of varying intensity will occur throughout the central valleys and northern mountains between 5 and 7 pm. PTYPE will be mainly rain across the Lower Susq Valley through the first half of tonight, then a rain/wet snow mix with up to a slushy 1 to 2 inches on the ridges around and to the north of the Greater Harrisburg Area. The snow should begin to taper off to scattered snow showers after midnight across the Laurel highlands but continue in most other areas.
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&& .SHORT TERM /10 PM THIS EVENING THROUGH 6 AM TUESDAY/... Ongoing winter storm overnight for Central PA, with biggest impacts shifting to the NE portion of CWA. Best dynamic cooling and highest QPF impacts areas north of I-80 from mid evening onward, though a band may extend from KIPT SW back toward KUNV/KAOO that may produce a couple of inches of wet snow if it gets intense enough. Transition to snow should be complete by mid/late evening in the NE, and high precip rates should produce a couple hours of snowfall rates of 2" per hour - so warning area still looks good. Precip looks to become light over the SW this evening with any significant snows ending with a general light snow persisting much of the overnight. Primarily a rain/snow mix late in the SE. && .LONG TERM /TUESDAY THROUGH MONDAY/... Winter storm impacts over North-Central/Northeast PA will come to an end by Tuesday afternoon as strong surface low continues to lift northeast along the Mid Atlantic/New England Coast. Strong WAA pattern quickly follows into mid week with high pressure ridge axis crossing the area on Wednesday. Maximum temperatures on Wednesday are fcst to climb well-above normal for late January. A well-advertised pattern change remains on track from the second half of the week into the weekend, with high confidence in a long wave trough carving out over the Eastern U.S. This will result in a prolonged period of seasonably cold temperatures and lake effect/high-terrain snow showers during the remainder of the period. Several inches of snow is probable in the typical locations like the Lake Erie Snowbelt. && .AVIATION /22Z MONDAY THROUGH SATURDAY/... A storm moving off the Carolina coast today will redevelop along the coast and moving up just east of NJ tonight and early Tuesday. Breezy across the SE today with strong easterly 850mb flow producing gusts in the 30s at KLNS. These will gradually subside through early evening. A gloomy day for Central PA ongoing as large area of rain and low clouds bringing cig/vsby restrictions to the region. Heaviest precip through 00z will be across the south and central. With atmosphere cooling, precip type will switch over to a wintry mix/snow in the Laurel Highlands /KJST/ late this afternoon and begin to mix with sleet or snow mainly in higher elevations elsewhere through 00z. Even enough instability to mention possibility of an isolated bolt of lightning here or there, but chance definitely too low for mention in terminals (except for a very short-range direct hit). Cooling continues this evening, with a transition to primarily snow mainly north of I-80, but edging back toward KUNV as well. Central Mountains will likely see a mix of rain/snow with the SE remaining primarily rain. Restrictions will continue, with conditions slipping to IFR just about everywhere. Improvement on Tuesday as storm lifts to the NE and precip comes to an end. Improvement arrives first over the SE half of CWA, though MVFR likely continues through the day. Outlook... Tue...Rain/snow ending in the morning. Widespread sub-VFR will improve for SE half by aftn. Wed...Low cigs/rain possible western 1/2. Breezy late. Thu-Fri...MVFR/IFR in rain/snow showers west. MVFR to VFR east. && .CTP WATCHES/WARNINGS/ADVISORIES...
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Winter Weather Advisory until 7 AM EST Tuesday for PAZ005- 010>012-017>019-025-026-045-046. Winter Storm Warning until 10 AM EST Tuesday for PAZ006-037- 041-042. Winter Weather Advisory until midnight EST tonight for PAZ024- 033.
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&& $$ SYNOPSIS...La Corte NEAR TERM...DeVoir/La Corte/Lambert SHORT TERM...RXR LONG TERM...Steinbugl AVIATION...RXR

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