Area Forecast Discussion
Issued by NWS State College, PA

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038 FXUS61 KCTP 210346 AFDCTP Area Forecast Discussion National Weather Service State College PA 1046 PM EST Fri Jan 20 2017 .SYNOPSIS... Relatively mild, but cloudy and unsettled conditions will persist through the weekend before cooler air makes a return next week. A complex and slow moving storm system is expected to move across the deep south then swing northeast along the Appalachians Sunday afternoon and night. The storm will then exit off the Mid Atlantic coast Monday and Tuesday and bring rain and perhaps a return of wintry weather. Much colder temperatures will arrive at the end of next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Current Obs and gridded LAMP and HRRR vsbys point twd the need of a Dense Fog Advisory over the NW Mtns and numerous SE counties and Schuylkill cty overnight through 13Z Sat. Sent out a recent collaboration message to surrounding WFOs regarding this. A few dwindling areas of light rain were drifting across the northern mtns of PA this evening. Elsewhere, skies were mostly cloudy to overcast with nothing more than some patchy light drizzle and areas of fog. A warm front close to the I-76 corridor in southern PA will lift slowly north across the forecast area overnight and Saturday. increasing dewpoints (into the lower 40s) over the colder, moist ground will allow fog to gradually thicken up to between 1/2SM and 1SM in many locations. Should any clearing occur, vsbys could quickly dip to AOB 1/4SM. In that case, consideration will have to be given for a Dense Fog Advisory. The temps will be nearly steady in most areas overnight, ranging from the upper 40s to around 50F across the Laurel Highlands, the lower to mid 40s across the Southern Valleys and NW mtns, and mid to upper 30s in the Central Valleys and Middle Susq Valley.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Some fog and drizzle will linger in the morning, and even into the afternoon on the ridges. Few if any breaks in the clouds are expected outside the far lower Susq as the lowest 3kft remain nearly saturated. Maxes are a tough call with lots of cloud cover, but an 8-12F rise is feasible. Will run with maxes just a hair under MOS blend. The central counties will probably top out in the m-u40s, but most other places will. 60F is possible, but not likely, in the Laurels and Warren Co. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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As the upper ridge is forecast to re-establish itself over the eastern U.S. early in the period, a very complex storm system is now forecasted to be settling over the Southwestern US by Saturday evening. This southern stream low should continue to track through the southern states before turning northeast over the eastern US Sunday night into early next week. The mid to long range models continue to trend warmer Sunday night into Monday. 850mb and 925mb Temperatures continue to be above 0C though a snow/rain mix remains possible in the higher elevations. Have rain as the main precipitation type. The forecast question through this period is QPF amounts. Based on latest models, blends, ensembles and national guidance, have increased QPF slightly based on PWATS, the moist southerly flow. One limiting factor could be probability of snow/rain mix, so higher QPFs are possible in the southeast. There remains a fairly large spread in QPF amounts in the plumes so will probably need to adjust amounts for later runs. Snow is possible beginning Monday across the Laurels within the region of greatest thickness cooling, then later Monday into Tuesday across the northern mountians and toward the Western Poconos. The combination of A backdoor Cfront sliding SWWD from New England and increasing baroclinicity as the deep low approaches the Mid Atlantic Monday night into Tuesday will allow the low to maintain its intensity and pull colder/sub-freezing air back into the NE and NCENT mtns. Most signif snow in oour CWA appears to target the Laurels and perhaps Sullivan and Tioga ctys in the NE. Any high pressure over the region will be short lived as a upper level low will settle over Eastern Canada. That system is progged to drag a cold front through the mid Atlantic Wednesday. After our early week storm system, the eastern ridge is made to make a rapid rebound, even if for just a short time around midweek. A fast moving shortwave quickly chews the top off the ridge with cyclonic westerly flow by week`s end. Colder air looks to advect into the region bringing in more winter like temperatures late next week.
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&& .AVIATION /04Z SATURDAY THROUGH WEDNESDAY/... IFR/LIFR stratus/fog covers nearly all of central Pa this evening northeast of a stalled warm front, which runs from western Pa southward along the spine of the Appalachian Mtns. Model soundings support continued low CIGs/fog overnight northeast of this stalled boundary. Exception may be at JST, which is straddling the warm front and is VFR at 03Z. A very close call here, as even a slight retrogression westward of front could lead to a return to IFR at JST overnight. Little improvement expected east of the Appalachians on Saturday, as models continue to show persistent low level moisture trapped beneath inversion to the northeast of stalled warm front. Best conditions will almost certainly be at JST, where VFR conditions appear likely west of front. Elsewhere, some modest improvement appears possible by afternoon, but IFR/low MVFR CIGs appear likely to persist through the day. Outlook... Sun...Low CIGs likely. Rain advances from S-N late. Mon...Rain/low CIGs likely. Tue...AM rain/snow and low CIGs possible. Wed...Reduced CIGs/showers possible NW. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo/Lambert NEAR TERM...Dangelo/Lambert SHORT TERM...Dangelo LONG TERM...Lambert/Ceru AVIATION...Fitzgerald

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