Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 201115 AFDCTP Area Forecast Discussion National Weather Service State College PA 715 AM EDT Tue Mar 20 2018 .SYNOPSIS... A complex winter storm system will move into the region today and continue through much of Wednesday. Drier weather will return for Thursday and Friday before a new storm system moves across the area this weekend. && .NEAR TERM /THROUGH TONIGHT/... A very complex winter storm is poised to affect the region. The latest model guidance made quite the increase in the QPF, necessitating a large adjustment in forecast thinking. The first chunk of the storm is already beginning to move into my far southern zones, an elongated area of mainly rain (at this time) is associated with a narrow area of low-mid level frontogenetic forcing between the right entrance region of the retreating upper jet entrance over NY/New Eng and the left exit region of the southern jet moving out of the Gulf States toward the Mid Atlantic. Surface temperatures over southern PA are near or even a bit above freezing, but the wild card is the dewpoints which are generally in the single digits. So even if the precip starts as rain, we will see quick column cooling as wet bulb effects become dominant. The first area of snow/sleet will mainly affect about the southern 1/3 of the forecast area into the afternoon hours, and the snow could fall heavy at times, though the exact placement of the heaviest snow remains a subject of disagreement among even the various high resolution near term model. For the first period I show the best chance of a moderate to heavy burst of snow being over my SWRN group of counties from Somerset-Cambria east to about Adams county. Models weaken the initial upper low as it approaches the region from the SW, while bringing a new chunk of upper energy up from the TN Valley overnight and Wednesday. The potential exists for a rather long period of moderate-heavy snow with a band of significant snow on the northern edge of the closed upper circulation over my SRN/SERN zones from later tonight into Wednesday afternoon. This sort of mesoscale forcing is very hard to pinpoint at this range so there is still much uncertainty in the forecast. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... If there are any lingering snow showers Wednesday night, they will move out quickly followed by breezy cool and drier conditions. && .LONG TERM /THURSDAY THROUGH MONDAY/... By Thursday...the storm will continue to slowly lift away from our area. An upper level low will drop southeast late Thursday into Friday. This will likely bring more clouds back into the area...with a chance of some snow showers. A complex pattern for the upcoming weekend into early next week will prevail. Central PA will likely be between a developing storm off the coast...and on the edge of warm advection from the central plains. Thus much of the time it should be dry. Main changes made was to adjust POPS down some for the weekend into next week...mainly to fit a little better with others. I did not want to change too much...given the large variation in model solutions. The other change was to adjust temperatures down after Thursday into the weekend...given northerly flow and source region of the airmass. && .AVIATION /11Z TUESDAY THROUGH SATURDAY/...
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For 12Z TAFS...main change was to slow leading edge of the snow down by an hour or so. Earlier discussion below. Patchy precipitation starting to work into Somerset County. Main leading edge to the snow is further south...between 30 to 100 miles from the PA border. Expect the snow to edge northward this morning...with perhaps some sleet at times. North flow of dry air will tend to slow the northward advance of the snow. There will be a tight gradient between VFR conditions across the far north later today...and IFR to MVFR conditions further south. Not much improvement to later Wednesday or early some snow will linger. Outlook... Tue night and Wed...Snow and restrictions continue. Some improvement later on Wed. Thu...No sig wx expected. Fri-Sat...A few snow showers possible.
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&& .CLIMATE... The Spring (Vernal) Equinox will be at 12:15 PM today, March 20. Sunrise in State College, PA will be 7:14 AM and sunset at 7:23 PM, for a total day length of just over 12 hours. While it will be spring on the calender today...a look outside will be more like winter. We may have to wait until late in the month to see a touch of spring-like temperatures. && .CTP WATCHES/WARNINGS/ADVISORIES...
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Winter Weather Advisory until 8 PM EDT Wednesday for PAZ017>019-045-049>053. Winter Storm Warning until 8 PM EDT Wednesday for PAZ024>028- 033>036-056>059-063>066.
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&& $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...La Corte LONG TERM...Martin AVIATION...Martin CLIMATE...Steinbugl is the U.S. government's official web portal to all federal, state and local government web resources and services.