Area Forecast Discussion
Issued by NWS State College, PA

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869 FXUS61 KCTP 170056 AFDCTP Area Forecast Discussion National Weather Service State College PA 756 PM EST Fri Feb 16 2018 .SYNOPSIS... High pressure will visit very briefly tonight, but be displaced Saturday as a quick shot of snow moves through late Saturday and Saturday night. Much warmer conditions are expected to make a return next week. && .NEAR TERM /UNTIL 7 AM SATURDAY MORNING/... Rain is gone, but flooding still on-going in Somerset Co. Most of the stream gages are headed downward, and expect problems to be over later this evening or early tonight at the latest. Prev... The back edge of the rain is quickly tapering to scattered showers, with a few snowflakes being observed over the Laurel Highlands. Hydro concerns continue for a couple of river points and probably at any number of isolated small streams and creeks as runoff from the rain and snowmelt continues into the evening. Overall water levels will begin to to fall. The river points at Shirleysburg and Williamsburg are expected to crest this evening and fall back below flood around or just after midnight. Drier and colder air will continue to move into the CWA overnight. Lows in the 20s will actually average several deg warmer than normal. && .SHORT TERM /7 AM SATURDAY MORNING THROUGH SUNDAY/... Judging by 18Z runs, the snow looks like it will start just an hour or so quicker than earlier estimates had it - starting in the Laurels before 3 PM, and spreading rapidly (as everything will happen with this quick shot) to the east and north. Model SLRs are around 12-14:1 for the event, but thinking is that it may be a little heavier/lower ratios as the temps will be above freezing at first, esp in the SE where maxes will flirt with 40F. However, faster snow also means faster cloud cover. Will keep temps the same. Will still allow for some melting at first in the warmer valleys, esp in the east. Because of the speed of the whole system most places will have only 7-9 hours of snow. Not all of this will be heavy, so the going amounts of a general 2-4 in the southern tier look good. Somerset County will start first and end last. Thus, there is a small worry for 6 inches there, esp on the west-facing slopes - but not enough (50%) of a worry to go with a watch or warning yet. Have posted an advy for all the southern counties, and all the SErn counties. Only the hill tops of the SE have any chance of getting to the 5" warning criteria there. The storm total snow map on the web shows a large area of 4-6" in the southeast, but that is made up of locations barely over 3.9" It is a weekend, so the evening drive time will be snowy but not as many people will be impacted compared to a weekday. Amounts north of I-80 look pretty sad - only an inch or so. A few counties from Blair east to Columbia could get close to 3" in spots. No advy yet for there, as time will help this forecast, but the other areas looked like sure bets. Prev... After a bright start, clouds will thicken with snow overspreading the area from SW to NE during the afternoon hours. The SPC HREF suggests this will be mainly a southern and southeastern PA storm so I went with the highest pops along and just north of the Mason-Dixon line and tapered things off toward NRN PA. The meat of the storm looks to be during a fairly small window from later Saturday through about midnight Sunday (Saturday night). The deepest moisture/best PWAT anomaly is made to scoot rather quickly off the Mid Atlantic coast south of the PA border. The SREF is more generous with the QPF while the GEFS doesn`t offer snow lovers nearly as much joy. The 12Z ECENS is pretty solid in the 2-4 inch range with maybe a tad more over the Laurels where some upslope could locally enhance amounts. Being mainly a 3rd period event, we chose to wait for later shifts to evaluate the need for any headlines. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Guidance continues to show a building anomalous upper ridge along the east coast next week. A period of rain appears likely Monday, as surface warm front lifts slowly through the area. After that, model guidance indicates central Pa will break into the warm sector with near record high temps possible Tue/Wed. Upper ridge is progged to weaken a bit late in the week with a cold front passage and associated showers likely Wed night or Thursday. Drier and cooler conditions appear likely Friday, but medium range guidance still indicating above normal heights across the eastern conus and ECENS MOS at least 10 deg above normal Friday. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/... For the 00Z TAF package...expect conditions to improve and winds to die down later this evening...as the cold front moves away from the area. Saturday starts off on the bright side with VFR conditions. High pressure will be over the area to start the day. A fast moving low moving across the southeast states and off the mid Atlantic coast Saturday evening...will bring snow and MVFR and IFR conditions to the area by mid to late aft. Far eastern areas like LNS...the snow may not start until shortly after sunset. Leading edge of the snow like recent events the last few days will be moving along at about 50 knots. The low is moving so fast...that other than maybe a few snow flakes and lower clouds early Sunday morning across the far west...most of Sunday will be sunny with VFR conditions. Outlook... Sun...Clearing, but A.M. restrictions west. Mon-Wed...Restrictions likely in periods of rain, especially the NW half early Monday. Much of the period may end up being dry with decent conditions. Showers will tend to move fast. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 4 PM Saturday to 2 AM EST Sunday for PAZ056>059-063>066. Winter Weather Advisory from 2 PM Saturday to 7 AM EST Sunday for PAZ024-033. Winter Weather Advisory from 2 PM to 11 PM EST Saturday for PAZ034>036. && $$ SYNOPSIS...La Corte NEAR TERM...Dangelo/La Corte SHORT TERM...Dangelo/La Corte LONG TERM...Fitzgerald/Gartner AVIATION...Martin

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