Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 182000 AFDCTP Area Forecast Discussion National Weather Service State College PA 400 PM EDT Wed Apr 18 2018 .SYNOPSIS... A rather compact but potent low pressure area will move overhead tonight and early Thursday. Blustery conditions and unseasonably cold temperatures will occur Thursday and Friday. A prolonged period of dry weather and slowly moderating temperatures is then in store. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Clouds pretty much gone from the srn half of the area as anticyclonic flow takes over for a few hours. The high clouds well back in nrn IL/IN will begin to expand and rather quickly eastward as WAA begins aloft ahead of a compact low crossing the Midwest attm. The low is directly under an equally compact upper low and will be whipped eastward by the well-timed arrival of a strong upper trough which deepens/sharpens as it drops out of ern Canada. These two features will combine to produce a quick burst of rain/showers beginning this evening in the west and exiting the NErn zones later tonight. However, it is the temperatures sfc and aloft which present the forecast problem of the day. Air temps are already very much sub-normal and will drop off as the evening begins. The sfc low looks to pass right overhead - most likely along the Turnpike - overnight. The winds will breifly go light and variable and then become NErly over much of the area as the low approaches. The Colder air to our north will be drawn down into the area and the wet-bulb/evap cooling effect will further cool things off as it begins to rain. Thus, it will be snowing much of the night in the north at varying rates. Expect much of the precip to the SE of the Allegheny Plateau to remain rain, but the higher elevations and over the Plateau will go to snow or at the very least a mix. SLRs will be only 8-10:1 = a fairly wet snow. The heaviest rain will occur in the preferred lift of the right exit region of a strong jet max. So, there is a potential for 3" of snow along the nrn tier of the state. Will work with the neighboring offices to come up with a good solution to this problem. We may end up being on an island as our criteria is only 3" in our nrn tier, while all the surrounding WFOs have a 4" threshold. Plus, guidance seems to center the heaviest snow in our nrn tier, and not so much outside our CWA borders. Min temps will be in the upper 20s in the north, but linger in the 40s over the SErn half of the area. As the low passes through and the wind becomes westerly behind it late tonight and early Thursday, it will get gusty. The middle of the road numbers mixing down the wind speeds over the Laurels and SC Mtns yields some gusts of 25-35kts. This should not necessitate a wind advy, but will make it feel pretty raw. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Temps only rise a deg or two tomorrow as CAA and wrap around clouds make it difficult to take advantage of the mid- April solar potential. If they even drop a deg or two, the precip over most of the area my be snow. But, will still call it mainly a rain/snow mix for the lower elevations. While some additional accums are possible Thurs, the main place to have anything stick will be those that have the snow already on the ground in the morning and the very highest elevations of the rest of the area. The gusty wind mentioned before will last much of the day across the southern third of the area and the north will ramp up to 25-30kt gusts at times. A blustery day for sure. A secondary push of colder air looks like it will cross the eastern zones under the aforementioned sharp upper trough, and could make quite a few showers for places just east of the Susq River. The temps may even be cold enough on the hill tops of the Poconos/Schuylkill Co to make snow stick. Post-frontal/cyclonic flow stratus/strato-cu remain for much of Thurs PM and a well-mixed lower atmos will keep the temps from dropping too far. So, the departure from normal mid-April values is only going to be a negative 5 to 10F. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Shallow stratocu and flurries will persist across the NW half of the state Thursday night, with partly cloudy skies in the SE. Winds should stay up enough through daybreak Friday to prevent a frost or freeze in the SE zones, while lows elsewhere dip into the mid 20s to low 30s. Friday and beyond, there will be a welcome break of lighter wind, sunshine and milder temps as a large area of high pressure moves out of the midwest. Yet another upper low in this busy pattern looks to drop into the deep south toward the end of the period. This may spread some precipitation northward toward our region for the beginning of next week. && .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... Rapid changes are expected from the mainly VFR sky this afternoon. A storm approaching from the west will rapidly spread clouds and rain into the area. The precip may begin as early as 01Z at JST and BFD. The temps should then get cold enough to turn the precip to all snow at BFD before midnight, and eventually/by sunrise at JST. Reductions to IFR and perhaps even LIFR are expected at BFD overnight and through the day on Thurs. JST should have the CIG lower to IFR well before the visby tanks. Elsewhere, the rain will be cold, but won`t start to mix with snow until very late tonight or during the day on Thurs. But, it will be a battle between marginal temps and the cold air shoving in during the daytime. Wind gusts will crank up after the low pressure area passes. It is expected to ride the PA Turnpike as it moves toward the east late tonight and very early Thurs. Wind gusts out of the west/northwest at JST and AOO will reach into the 30s on Thurs, with 20s elsewhere. SHRASN linger all day, and taper off Thurs PM. The clouds will feature a typical post-frontal pattern to them, with MVFR/VFR for most of the area Thurs and Thurs PM. The only places which may see IFR after 15Z Thurs will be JST and BFD. Conditions improve drastically Fri with the arrival of a big high pressure area which will last through the weekend. Outlook... Fri...MVFR cigs nw 1/3; VFR elsewhere. Sat-Mon...VFR/no sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES...
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Winter Weather Advisory from midnight tonight to 4 PM EDT Thursday for PAZ004>006-037.
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&& $$ SYNOPSIS...Dangelo/Lambert NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...Lambert/Gartner AVIATION...Dangelo CLIMATE...

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