Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 262315 AFDCTP Area Forecast Discussion National Weather Service State College PA 715 PM EDT Sun Mar 26 2017 .SYNOPSIS... A cool-moist easterly flow will keep it damp over most of the forecast area. A frontal system will move back into the region overnight and remain nearly stationary before a cold front finally ushers in cooler and drier air during the day Tuesday. The drier conditions will continue for mid week before a new storm system approaches for the end of the week. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... The region remains firmly ensconced in a low level cold air damming pattern late this afternoon. New high resolution GOES-R 1 minute visual loop shows the stable low clouds being passed over by the more broken mid and high clouds. The only part of the area not locked into the cold air damming is Warren County, where some sun is helping temperatures climb into the mid 50s. Regional radar loop at 2030Z showing first band of showers moving into the Laurel Highlands associated with approaching shortwave. HRRR and 18Z NAM show southerly low level jet lifting across central Pa overnight, resulting in an increasing likelihood of rain over the central counties early this evening and east of the Susquehanna River after dark. Blend of near term models support rainfall overnight of between a quarter and half inch over much of central Pa, with a bit less over the Lower Susq Valley. Although just about the entire region will remain in stable air east of stationary front, models indicating enough elevated instability ahead of shortwave to perhaps support a few rumbles of thunder overnight, mainly across the western counties. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... Low level stability indices indicate that the the surface warm front will try to lift NE across the CWA late tonight and Monday morning as it`s associated sfc low moves down the St. Lawrence River Valley as a weakening feature. The new GFS and NAM suggest that a lull in the shower activity will take place late tomorrow morning and afternoon as the remnants of the diffuse warm frontal boundary fall apart over northern PA/southern NY in favor of the stronger thermal pattern that re-establishes south of the region ahead of an approaching new storm system. This leaves a weak flow pattern in place for the afternoon, likely still more clouds than sunshine but with the chance for some breaks helping temperatures returning to something much more palatable than today`s chilly 40s. Highs should make it into the mid 50s, and range to the lower 70s along the MD border. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... This period starts out with above normal heights over the eastern U.S. Several lows weaken as they move into this blocked flow and are forced to move to our west. The first wave is comes overnight tonight into early Monday. It has a good surge of moisture and one or more distinct ribbons of llvl theta-e convergence that should result in some nearly north-south oriented bands of briefly heavier showers. Thus nearly all operational and blended/ensemble guidance shows a very high probability of rain overnight tonight into Monday. Most of the guidance shows the peak chance of rain from 0000-1200 UTC Monday. Then things improve during the day Monday. The second wave moving northeast and right up the Ohio River Valley comes in overnight Monday into Tuesday. Another similar surge of +2-3 sigma Pwat air precedes the passage of this area of low pressure and will once again result in a high probability for showers, but generally light to locally moderate 12 hour rainfall amounts. The second event will push the warm moist air off to our south Tuesday night into Wednesday. Chance of rain should drop overnight Tuesday into Wednesday. Wednesday should be a relatively good day as high pressure builds in from the northwest. The dry air and high pressure are in all the 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. && .AVIATION /23Z SUNDAY THROUGH FRIDAY/...
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Made a few more changes here at 7 PM. Second band of showers now in western PA. Band over OH not so widespread in nature. Earlier discussion below. First band of showers falling apart, as it moves into central PA. Several more bands of showers over OH. Made some changes to 21Z TAF package, some of which will be used in the 00Z TAF package. Expect some improvement later Monday, as winds shift more to the southwest. A moist east/southeast low level flow will support widespread low MVFR to LIFR conditions into Monday. Aside from pockets of drizzle/mist/fog, the main period of rain should be tonight between about 27/00z to 27/12z, tapering off from west to east Monday morning. Conditions will improve slowly later Monday morning with central and eastern terminals likely rising to VFR by early to mid afternoon. A stray afternoon thunderstorm cannot be ruled out, especially over the south. Outlook... Tue...Sub-VFR with periods of rain. Wed...MVFR becoming VFR early. Thu...VFR early, Increasing chance of rain and lowering conditions late in the day into Thursday night. Fri...Breezy with showers. MVFR to IFR conditions possible.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte NEAR TERM...Fitzgerald/La Corte SHORT TERM...La Corte LONG TERM...Grumm/Lambert/Gartner AVIATION...Martin

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