Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 260945 AFDCTP Area Forecast Discussion National Weather Service State College PA 545 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/... 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 Sunday into early Monday. It has a good surge of moisture and a boundary related to the cooler weather on Sunday. Thus nearly all guidance shows a very high probability of rain overnight Sunday 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 up to our west comes in overnight Monday into Tuesday. Clearly the uncertainty with this and the longer forecast length introduces more uncertainty. But at this time peak rain probabilities are during the day Tuesday but lower probabilities than the first event. The second event will push the warm moist air 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. The storm track shifts to our south and some models show a southern stream wave Thursday night and Friday. This could bring clouds to our region. GEFS and CMCE imply we could be on the northern edge of an expanding precipitation shield Friday and Saturday as the southern stream wave slides to our south and east. Thus POPS increase Friday and Saturday. Could be a cold rain across south-central PA Friday and Friday night. && .AVIATION /09Z 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...Grumm/Lambert AVIATION...Steinbugl

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