Area Forecast Discussion
Issued by NWS State College, PA

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994 FXUS61 KCTP 202017 AFDCTP Area Forecast Discussion National Weather Service State College PA 317 PM EST Tue Feb 20 2018 .SYNOPSIS...
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Temperatures 25 to 35 degrees above average will be common this afternoon, and again on Wednesday, making it feel more like May than February. A strong cold front will move southeast across the commonwealth during the day Wednesday, followed by several weak waves of low pressure bringing bouts of rain for the second half of the week, and even some light freezing precipitation Thursday morning. Another significant warm up is possible on Sunday.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Middle to Lower Susquehanna Valley slowest to warm this afternoon given ageostrophic llvl flow/weak mixing, but the remainder of central PA is downright toasty for February this afternoon with widespread 60s and 70s delighting the locals thanks to a fresh southwest breeze. Mid to late afternoon surge will hopefully warm the rest of my eastern counties to near 60 so that noone is left out. Isolated light showers are brushing the northwest mountains at mid afternoon. These will last for another hour or two with most areas seeing non measurable amounts. A mild night is in store for most as coupled southwest flow maintains southwest flow over the region. Far eastern areas will warm this afternoon, but won`t completely scour out, and as a result expect another round of fog and low clouds late tonight into Thursday morning. Mins will range from the middle to upper 50s across the west, and lower to middle 50s central and easy with some upper 40s likely over portions of the Middle to Lower Susq River Valley. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... The warmth continues into Wednesday, with a spring like start to the day. Areas of fog especially east will give way to mixed clouds and sun with near- record to record high temps across much of portions of Central and Western PA. A weakening area of showers will accompany a cold front dropping across the commonwealth Wednesday, begining mid to late morning NW and reaching into the Lower Susq. by evening. This will hold down highs over the northwest, but allow another day of 60s and 70s elsewhere. Showers will accompany the front later Wed morning (NW) and during the afternoon and evening elsewhere across the Central Mountains, then Lower Susq Valley. Considered thunder possibility but instability appears absent this go around. Colder air to come Wednesday night thanks to strong 1040 mb high pressure buildings eastward from the Midwest. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
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Did not change a lot for the period Wednesday night into Friday. Current fcst looks good. Potential for a significant change in practical weather...if frontal position changes very much. Some downward adjustments made earlier today on ice amts. My main change was to add additional grids. Still looking like another warm up on Sunday. Potential for some heavy showers across the west...but several days out. Still looks dry behind the front Sunday Night...so I took out the showers of the fcst after 06Z Monday. Left Monday into Tuesday dry...weak system fcst to cut under the ridge...but not seeing much moisture with this. More information below from earlier shifts. *Periods of rain with a several hour period of icing from freezing rain expected late Wed night through Thur morning. brief interval of mixed precip possible Wed. night- AM Fri. A light accumulation of snow could precede the freezing rain across the Northern Mountains early Thursday. *Pattern favors above average temperatures this weekend into next week The cold front will become quasi stationary near the MD line Wed. night. The wavy frontal boundary will bring periods of rain into the weekend, with several (to as much as 8) hour period of mixed wintry precip likely across mainly the Central and northern mountains Wed. night and Thu morning, thanks to an increasing and moderately strong northerly, 1000 mb Ageostrophic flow that will serve to pump shallow/sub-freezing air south into the region. Confidence is moderate with respect to the exact ptype details (and the location and amount of fzra). However, there is at least some risk for a light snow and/or ice accumulation. We`re in good agreement with WPC`s Winter Weather graphics ATTM, with a coating to 2 inches of snow possible at the onset across parts of northcentral and NW PA, before a changeover to sleet and or Freezing Rain. Another round or two or rain is likely over the weekend. We will need to monitor the potential for flooding especially across south- central PA where the ground is very saturated from previous rain/snowmelt and streamflows are well above normal.
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&& .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Most areas improved to VFR for this afternoon, except for KIPT which keeps some MFVR cigs into mid afternoon.Patchy fog / low ceilings edge back into the Susq Valley from the east tonight into Wed morning, then give way to VFR conditions across most of the region. Exeption will be over the NW Mtns as a sharp cold front will spread rain and restrictions in from the NW, with restrictions possible in the afternoon/evening into the central mountains. That will be followed by several weak waves of low pressure bringing bouts of rain for the second half of the week, and even some light freezing precipitation Thursday morning. Outlook... Wed...Restrictions likely in rain showers mainly NW half. Thu...Widespread restrictions in rain south/wintry mix north. Fri-Sat...Widespread restrictions in periods of rain. && .HYDROLOGY... Recent rainfall and snowmelt has resulted in very saturated soil and well above normal streamflows across much of the area especially south-central PA. Rainfall of 0.50 to 1.00 inch is forecast between Wednesday and Thursday night, with additional rainfall likely into/over the weekend. River flood potential (including small streams, creeks and tributaries) is above normal and we will continue to monitor the risk in the coming days. && .CLIMATE...
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Looks like some sites at or above record highs for today. CLI data will be out by 530 - 6 PM. See CLI data for more details later this aft. Record highs for selected sites for Tuesday and Wednesday February 20th and 21st: MDT: 72/1930;71/1997 IPT: 67/2016;69/1930 BFD: 58/2016;64/1997 AOO: 62/2016;71/1997
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir/Martin NEAR TERM...DeVoir SHORT TERM...DeVoir LONG TERM...Lambert/Martin AVIATION...DeVoir/RXR HYDROLOGY...Lambert CLIMATE...Lambert/Martin

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