Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 261110 AFDCTP Area Forecast Discussion National Weather Service State College PA 710 AM EDT Sun Mar 26 2017 .SYNOPSIS... A cool and moist easterly flow will prevail today, helping to create widespread low clouds and some light drizzle at times. The chance for rain will increase late today over Western Pennsylvania, and tonight elsewhere across the Central and Eastern portions of the state as a wave of low pressure moves northeast from the Mid Mississippi valley to the Upper Great Lakes region, and pushes a warm front northward across the District. Rainfall amounts late today into early Monday will average between one-quarter and one-half of an inch. Unseasonably mild conditions are expected tonight through Tuesday. Cooler and dry weather will follow for Wednesday and Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Backdoor cold front has pushed south across the Virginias and west into ohio as of early this morning. Persistent...cool and moist easterly flow will maintain overcast skies all day with mainly dry conditions. However...the ridge tops and east facing slopes will see the cloud bases intersecting them with periods of light drizzle too. Max temps today were weighted heavily toward the NAM. The NAM limits highs to the 40s for many locations...and even holds readings in the upper 30s across some of the higher terrain throughout the NE corner of our CWA. This is in comparison to the much warmer (by 8-10 deg F) National Blend of Models where its GFS core lacks the boundary layer detail to adequately capture the shallow cold airmass being channeled through the deep valleys of Central PA. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... An upper low an increased Diff PVA will approach from the Ohio Valley late in the day, bringing a renewed chance of showers across the Alleghenies and Central Mountains toward evening. Can`t rule out a rumble of thunder across the Alleghenies, although any convection will be weakening rapidly as it encounters the shallow and very stable/cool airmass entrenched throughout Central Pa. Sfc warm front will try to lift NE across the CWA late tonight as it`s associated sfc low moves NE across the Upper Great Lakes. Widespread clouds and relatively mild temps will persist overnight with lows in the 30s to low 40s. Energy aloft and a core of 50 kt South-southwesterly accompanied by a few bands of moderately strong low-mid level Theta-E convergence will bring periods of rain with one quarter to one half inch of rain falling. The heaviest rainfall will be over the western mountains where localized amounts of 0.75 to 1.00 inch area possible. && .LONG TERM /MONDAY THROUGH SATURDAY/...
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This period starts out with above normal heights over the eastern US. 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 NCEP guidance shows the peak chance of rain from 0000-1200 UTC Monday. Then things improve during the day Monday. Our POPS Monday morning may be too high, but they remain consistent and well-collaborated with surrounding forecast offices. GEFS implies little or no rain in our CWA much after 1800 UTC Monday. Most rain before then would be in the east. Our 850 hPa temperatures are above normal too so should be a warm later afteroon and evening. 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.
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&& .AVIATION /12Z SUNDAY THROUGH THURSDAY/... IR satellite confirms observational trends and near-term model guidance in developing widespread low clouds/ceilings across the airspace this morning. A moist east/southeast low level flow will support sub-VFR conditions with low MVFR to IFR fcst terminal-wide by afternoon. Question remains how quickly cigs could lower to IFR and timing adjustments/amendments may be necessary going forward. Aside from some patchy drizzle or mist, the main period of rain should be from around 27/00z to 27/12z. Outlook... Mon-Tue...Sub-VFR with periods of rain. Wed...MVFR with chance of rain early in the morning, then becoming VFR. Thu...Increasing chance of rain late in the day into Thursday night. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/Grumm AVIATION...Steinbugl

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