Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 211509 AFDCTP Area Forecast Discussion National Weather Service State College PA 1009 AM EST Wed Feb 21 2018 .SYNOPSIS...
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A cold front will push southeast across the area this afternoon and evening, then stall out in the vicinity of the Mason-Dixon line or across the Virginias late this week into the upcoming weekend.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The cold front as of 10AM extends from between BFD and ERI southwest into south-central OH. Radar indicates this is an almost classic anafront with an area of rain along and behind the front. It will be another unseasonably warm day for most of the forecast area with highs reaching well up into the 60s and 70s before cooler starts to ooze in behind the cold front. These temps will depart by an amazing 35 deg F from normal highs in Late Feb. The HRRR shows the cold front from about IPT to JST by 18Z/1PM, and passing through the lower Susq Valley between 4 and 7PM. I inserted the mention of thunder over the SE given the latest HRRR generating some instability in the warm and moist airmass. Dewpoints are approaching 60 over the SE where it no doubt feels quite humid for the time of year. Another trend in the HRRR and NAM based CAMs is to show the rain really falling apart as it enters the Central Mountains today, becoming more scattered and showery. I trimmed POPs a bit to try and depict this more optimistic scenario. Rainfall totals will be generally light and less than 0.10 of an inch.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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Periods of rain (with a several hour period of icing from freezing rain across northern PA) is expected late tonight through Thur morning across the northern half of PA. A light accumulation of snow could precede the freezing rain across the Northern Mountains early Thursday. Colder/drier air will temporarily filter south into the region this evening thanks to strong 1040 mb high pressure buildings eastward from the Midwest. Stalled frontal boundary south of Pa will begin to return northward late tonight, spreading rain into much of the region, with mixed precip likely along the northern tier. The cold front will become quasi-stationary near the MD line tonight. 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 tonight 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 across primarily the northern Mtns of PA). 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.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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Forecast for Thursday into Friday looks cloudy and damp with periods of light rain/drizzle and areas of fog. The fog will be locally dense at times, especially on East-Facing slopes and ridgetops during the overnight and early to mid morning hours. Stalled out sfc front across the Virginias and Ohio River Valley and SW flow aloft will be the conduit for a few waves of low pressure to ripple NE along, and bring us this rather dismal weather. There is the potential for a significant change in practical weather...if frontal position changes north or south very much. 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. 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 /15Z WEDNESDAY THROUGH SUNDAY/... Patchy dense fog impacting eastern portions of CWA (generally east of the Susq River) this morning under strong low level inversion. Vsbys should improve back to VFR at MDT-LNS by ~14z while it may take a couple of hours longer in the protected valley of IPT. Elsewhere, outside of some very patchy fog, conditions will be primarily VFR until arrival of a cold front. LLWS the first half of the day will gradually weaken, but also begin to mix down to the surface as inversion erodes - allowing SW winds to pick up to around 10 mph gusting to 18 mph across the western valleys and 15 mph gust to 25 mph on the ridges. Winds over the east will remain generally less than 10 mph. A sharp cold front will move into the NW Mtns late this morning, bringing reductions in rain. These impacts will attempt to spread into portions of the central mountains during the afternoon before improvement back to VFR this evening. Showers do spread into the SE late this afternoon as well, but conditions will remain primarily VFR there. Winds turn to the west over the Lower Susq and NW elsewhere. An active second half of the week follows, as several weak waves of low pressure bringing bouts of rain, and even some light freezing precipitation to the north Thu into early Fri. Outlook... Thu...Widespread restrictions in rain south/wintry mix north. Fri...Widespread restrictions in periods of rain. Some improvement poss SW late. Sat...Rain remains likely. Widespread restrictions north, gradual improvement south. Sun...Widespread restrictions likely in periods of rain. && .HYDROLOGY... Recent rainfall and snowmelt has resulted in wet 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... It Looks like another day of record highs across southern Pa today. Here are current records for today, Wednesday February 21st: MDT: 71/1997 IPT: 69/1930 BFD: 64/1997 AOO: 71/1997 && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte/Lambert NEAR TERM...La Corte/Lambert SHORT TERM...DeVoir/Fitzgerald LONG TERM...Lambert/Martin AVIATION...RXR HYDROLOGY... CLIMATE...

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