Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 272006 AFDCTP Area Forecast Discussion National Weather Service State College PA 406 PM EDT Mon Mar 27 2017 .SYNOPSIS... An area of low pressure will move along or just south of the Mason-Dixon line late tonight and Tuesday. High pressure will build down out of southern Canada and bring cooler and drier weather for Wednesday and Thursday. A new storm system will approach for the end of this week with the potential for more inclement weather. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... The drier air has scoured out the low clouds over all but the far north and much of the mid and lower Susq Valley where the cold air damming is tenacious. Even there however the milder and drier air should mix down by mid afternoon, at least for a brief time anyway. Despite the projections of some modest instability in the RAP, the HRRR keeps a lid on things for the rest of the day. So I lowered the already low chances for a pop up shower or thunderstorm over the far south, especially in the areas still plagued by the cool-moist maritime airmass. Clouds will tend to return with a renewed chance of showers once again tonight as the next wave of low pressure moves into Ohio. Lows will be very mild in the 40s to lower 50s. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... Latest NAM/GFS show the surface wave taking a track over or just south of the PA-MD border during the day Tuesday bringing occasional showers that will taper off from NW to SE during the afternoon. The guidance once again shows the development of some instability over southern areas so a thunderstorm cannot be ruled out. It will likely be subject more to the amount of sunshine that can develop than dynamic forcing. It will be another mild day in the 60s in most locations. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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The long term period will start with a frontal system and associated precipitation exiting the region and heights building aloft. Building high pressure will push the warm moist air off to our south Tuesday night into Wednesday. Wednesday should be a relatively nice day (though with some mdt northerly wind gusts at times, as high pressure builds in from the northwest. The dry air and high pressure are in all of the most recent guidance, implying Wednesday and Thursday should be relatively nice days. High pressure, dry air, and normal to slightly below normal 850 hPa and 925 hPa temperatures imply near normal daytime highs. Most of the 26/00-06Z U.S. and int`l model guidance (and EFS) indicates more of southern...shearing storm track for late in the week...thanks to a stronger and more wwd position of a deep nrn stream vortex across the Canadian Maritimes. The trend of the big model discrepancy for late this week and this weekend (between the GFS and EC over the past several days) has trended toward the GFS and its ENS members with southern stream energy and its moisture being prevented from amplifying with an associated storm track to our west. Rather, what we see is a shift of the primary southern stream sfc low track to our south as the potent midweek southern stream sfc/upper low (that will be trying to take the turn northeast across the Mid Miss Valley twd the Great Lakes) encounters great resistance from the notably stronger WNW upper jet core defining the northern stream that will be situated from the Upper Glakes to the Mid Atl Coast. With this type of consensus storm track, pops will be somewhat less for Friday and Saturday (compared to a heavily weighted EC/ECENS solution) and limited to mainly the southern half of PA where some rain (or even an elevation-dependent rain/wet snow mix) with expansive cooler and drier air north of PA.
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&& .AVIATION /20Z MONDAY THROUGH SATURDAY/... The drier air is mixing into central PA quickly as of early afternoon. The exception is over the Susq Valley where MVFR/IFR conditions continue. Even here however the drier air will manage to invade between about 3 and 5 pm. Unfortunately the VFR conditions this evening will deteriorate once again overnight as a new storm system spreads showers our way. Widespread IFR/MVFR will be the rule Tuesday along with occasional rain showers and even the small chance of an afternoon thunderstorm over the south. Outlook... Wed...MVFR NW 1/3 becoming VFR. Thu...VFR/No sig wx. Thurs night-Sat...Sub-VFR restrictions/rain likely. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...La Corte LONG TERM...Lambert/Gartner AVIATION...La Corte

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