Area Forecast Discussion
Issued by NWS State College, PA

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586 FXUS61 KCTP 190851 AFDCTP Area Forecast Discussion National Weather Service State College PA 451 AM EDT Thu Apr 19 2018 .SYNOPSIS...
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A rather compact but potent low pressure area will move east from the Ohio Valley and take aim on the Laurel Highlands and adjacent portions of Central and Southern Pennsylvania today. Occasional light snow or snow showers will bring a light accumulation of a coating to around one inch to the higher terrain of northern and western Pennsylvania today. The ridge tops of the Laurel Highlands could see locally higher amounts of around 2 inches. Blustery conditions and unseasonably cold temperatures will occur Today and Friday. A prolonged period of dry weather and slowly moderating temperatures will follow for the upcoming weekend through at least the first part of next week as a large area of high pressure drifts from the Upper Midwest to the New England states.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Current system affecting the region today displays a much more detached warm/cold conveyor belt and lighter associated QPF than was advertised by a host of short range model guidance at this time Wednesday morning. Additionally, the sfc low is weaker by 2-4 mb and more fragmented while taking a more southern track across the Virginias (than previously depicted). These notable changes have impacted (lessened both our snowfall and wind forecasts). Recently dropped the Winter Weather Advisory that was in place across our northern tier, since the warm advection snows likely only accumulated one half of an inch at best considering borderline temps and just a 60-90 minute period that afforded the chc for briefly moderate snowfall rates between 05-08Z. The main (and quite compact) cold conveyer belt snows falling across NE Indiana and Northern Ohio ATTM, will slide ESE through the rest of this morning, and should spread over the Laurel Highlands and bring a coating to 2 inches of snow accum between about 12-16Z today. Elsewhere, any steadier precip will be brief or non-existent today, though much colder temps advecting into the region within the 850-500 mb layer will steepen lapse rates and generate scattered-numerous snow showers across the Mountains of North-Central and NW PA through early this afternoon with perhaps a coating...up to around an inch on grassy areas across the higher elevations. Expect much of the precip to the SE of the Allegheny Plateau to remain rain through the mid morning hours, but the higher elevations and over the Plateau will go to wet snow, (or at the very least a mix). SLRs will be less than 8:1 = a fairly wet snow. The heaviest rain (that will exit the SE third of our CWA over the next few hours) will occur within the preferred lift/thermally indirect cell associated with the left exit region of the quite strong upper level jet max (over 100 Kt at 300 MB). The middle of the road numbers mixing down the wind speeds over the Laurels and SC Mtns yields some gusts of 25-35kts. This shouldn`t be nearly enough to necessitate a wind advy.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
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Temps only rise a deg or two today 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.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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Shallow stratocu and flurries will persist across the NW half of the state Thursday night and early Friday, 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.
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&& .AVIATION /09Z THURSDAY THROUGH MONDAY/...
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06Z TAFS sent. Patches of rain racing northeast at 50 mph. Earlier discussion below. VFR conditions across the area this evening will quickly give way to reductions working in from the west after 04z as an approaching storm begins to move through. Some light showers developing out ahead of the main show, but majority of precip will hold off until after 04z. The temps should then get cold enough to turn the precip to all snow at BFD before midnight, and eventually/by sunrise at JST as colder air sweeps in from the NW. Reductions to IFR 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 which should keep visbys above IFR in many places. WNW winds will become strong and gusty after the low pressure area passes - just after daybreak Thurs. Gusts across the south will reach into the 30s, with 20s elsewhere. -SHRASN linger all day, and taper off late. The clouds will feature a typical post-frontal pattern to them, with MVFR/VFR for most of the area. 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.
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&& .CTP WATCHES/WARNINGS/ADVISORIES...
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None.
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&& $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/Gartner AVIATION...Martin/RXR

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