Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 201837 AFDCTP Area Forecast Discussion National Weather Service State College PA 237 PM EDT Tue Mar 20 2018 .SYNOPSIS... An early spring, long duration winter storm will bring heavy snow to parts of south-central Pennsylvania through Wednesday. Dry weather with cooler than average temperatures is expected Thursday and Friday. && .NEAR TERM /THROUGH TONIGHT/... Narrow band of moderate to heavy snow has been slowly pivoting northward over far south central PA, mainly along and south of US-22/I-76. The heavy snow rates and strong evaporational cooling/wet bulb effects are overcoming marginal surface temperatures and time of day/year factors with accumulation on roads per webcams, spotter and social media reports. Rates up to 2" per hour have been observed. Main change to the forecast this morning was to tighten up the northern edge of snowfall and increase amounts a bit over the higher elevations in south-central PA. The 00Z HREF mean shows 12+ inch max snowfall totals over far south-central PA generally east of the Laurels, so local amounts over a foot are supported. With plenty of dry air in place over northern PA (dewpoints in the single digits) expect an extremely tight gradient/range and cut/off zone from north of US-22 to I-80. Areas near and especially to the north of I-80 may see little to no accumulation. The latest HRRR/HRRRx and 00z HREF support the sharp northern edge to the snowfall. We will try to reflect this in "where" bullet of the updated WSW. Previous/Tonight: Models weaken the initial upper low as it approaches the region from the SW, while bringing a new chunk of upper energy up from the TN Valley overnight and Wednesday. The potential exists for a rather long period of moderate-heavy snow with a band of significant snow on the northern edge of the closed upper circulation over my SRN/SERN zones from later tonight into Wednesday afternoon. This sort of mesoscale forcing is very hard to pinpoint at this range so there is still much uncertainty in the forecast. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... If there are any lingering snow showers Wednesday night, they will move out quickly followed by breezy cool and drier conditions. && .LONG TERM /THURSDAY THROUGH MONDAY/...
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By Thursday...the storm will continue to slowly lift away from our area. An upper level low will drop southeast late Thursday into Friday. This will likely bring more clouds back into the area...with a chance of some snow showers, and keep temperatures on the cooler side. A complex pattern for the upcoming weekend into early next week will prevail. Central PA will likely be between a developing storm off the coast...and on the edge of warm advection from the central plains. Thus much of the time it should be dry, but remain cool in low level northeasterly flow. By Sunday night into Monday, another upper wave slides through with ridging and cool surface high building in behind.
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VFR conditions persist over northern half of CWA as dry air continues to fend off precip approaching from the south. Areas north of I-80 should remain VFR through the TAF period. Snow/areas of mixed precipitation impacting southern half of CWA this afternoon with widespread restrictions. Precip intensity should lighten for several hours this evening before picking up again late tonight into Wednesday with another period of moderate to heavy snow likely, especially across SE portions. Restrictions will continue, with widespread IFR esp along and south of the PA Turnpike, until conditions begin to improve from the north late Wed into Wed eve. LLWS becomes likely over the south late tonight into Wed as 850mb jet increases to 30-40 kts as it rotates from the east to the northeast. Outlook... Tonight and Wed...Snow and restrictions continue southern half. Some improvement later on Wed. Thu...No sig wx expected. Fri...Cig restrictions poss NW. Sat-Sun...No sig wx expected.
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&& .CLIMATE... The Spring (Vernal) Equinox will be at 12:15 PM today, March 20. Sunrise in State College, PA will be 7:14 AM and sunset at 7:23 PM, for a total day length of just over 12 hours. While it will be spring on the calender today...a look outside will be more like winter. We may have to wait until late in the month to see a touch of spring-like temperatures. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 8 PM EDT Wednesday for PAZ017>019-045-049>053. Winter Storm Warning until 8 PM EDT Wednesday for PAZ024>028- 033>036-056>059-063>066. && $$ SYNOPSIS...Steinbugl NEAR TERM...Steinbugl SHORT TERM...La Corte LONG TERM...RXR AVIATION...RXR CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.