Area Forecast Discussion
Issued by NWS State College, PA

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660 FXUS61 KCTP 231020 AFDCTP Area Forecast Discussion National Weather Service State College PA 520 AM EST Mon Jan 23 2017 .SYNOPSIS... A storm will move through the Carolinas early today before redeveloping along the coast and moving up just east of NJ 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 /THROUGH TONIGHT/... * Major cyclone to affect the region today and tonight * Elevation dependent snow storm likely * Heavy wet snow not out of the question even into central ridge-valley areas * Strong easterly LLJ 50-65kt/5-7 sigma * High probability of at least 1" QPF over much of central PA * Explosive dynamic cooling leads to steep mid level lapse rates-thunder snow? The deep storm that has been responsible for several rounds of severe storms and deadly tornadoes over Dixie, will move east and redevelop in the vicinity of the Delmarva coast, before swinging up along or just off the NJ coast. The wind has picked up a bit tonight allowing the very low visibilities to mix out somewhat as spotty light rain and drizzle have few NW over the area. The HRRR shows the rain continuing to fill in as it moves NW into central PA this morning. Then things get complicated and interesting. As strong vertical motion forces rapid dynamic cooling aloft, precipitation type issues will arise quickly by late morning and this afternoon. We start off so anomalously warm it`s hard to believe a significant snow storm is possible but it looks very likely for at least my northern higher elevation counties. The deterministic ECMWF shows several inches of snow even down into the Laurel Highlands. The EC ensemble is even more generous with its depiction of 6+ inches, though it is notoriously generous with the snow its algorithm produces. Right now I show a rain to rain or snow scenario for central areas where the higher elevations seem most at risk for accumulating snow, but even down in the valleys, if we see heavy enough precip rates we could share in the snow-joy. A tightening pressure gradient between low pressure in the Carolinas and high pressure in eastern Quebec will produce strong/gusty east winds this morning into the afternoon, the best threat area being our SERN zones. We tend to have a hard time mixing the best winds down under what is essentially a cool air damming set up, but with 50-65 kts aloft, strong gusts cannot be ruled out. It`s a very complicated situation and will likely lead to many near term tweaks as things play out today. I generally used the ECMWF to show the steadiest/heaviest snow lasting into tonight over about the NERN 1/3 - 1/2 of my forecast area as the upper low swings offshore and we see the deformation zone gradually rotate through. Meso-scale banding under this feature could cause locally higher amounts than the general 6-10 inches I have in the forecast at this time. The snow should begin to taper off to scattered snow showers after midnight. && .SHORT TERM /TUESDAY/... As the storm system pulls away toward the coastal waters south of New England tomorrow, rain or snow showers will tend to be most frequent in the morning and become more scattered in the afternoon. Highs in the mid 30s to mid 40s will still be several degrees warmer than normal. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... After a brief break and mild conditions for mid week, a pattern shift is advertised for the second half of the week as low pressure takes up residence over eastern Canada, and despite a tenacious ridge over the northern Caribbean and Bahamas, models carve out a long wave trough over the eastern US with a return to seasonable cold by the end of the week into next weekend. It points to a prolonged period of cloudy breezy and colder weather with mainly mountains snow showers that will occasionally bleed down into central areas. && .AVIATION /10Z MONDAY THROUGH FRIDAY/...
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09Z TAFS sent. Cooling tops over WV now, in the area that is fcst to have a cold pocket at 850 mb form. The second part of the puzzle is if the area of precipitation will fill in. At the current time, several bands of rain well to the south of our area. Thus for the next few hours, the main issue is gusty winds. Later on, expect the area of rain to fill in. Then at least sites like BFD and JST are likely to see some heavy wet snow this aft into tonight. Other problems will be LLWS, given that strong winds have formed since midnight. Some chance of thunder, given strong upper level support. Outlook... Tue...Widespread sub-VFR with some improvement by aftn. Rain/snow ending in the morning. Gusty winds from NNW decreasing late. Wed...Low cigs/rain possible western 1/2. Breezy late. Thu-Fri...MVFR/IFR in rain/snow showers west. MVFR to VFR east.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 4 PM this afternoon to 7 AM EST Tuesday for PAZ005-010>012-017-018. Winter Storm Warning from 1 PM this afternoon to 10 AM EST Tuesday for PAZ006-037-041-042. Wind Advisory until 4 PM EST this afternoon for PAZ057-059- 064>066. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...La Corte LONG TERM...La Corte AVIATION...Martin

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