Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 201133 AFDCTP Area Forecast Discussion National Weather Service State College PA 733 AM EDT Fri Oct 20 2017 .SYNOPSIS... A large and persistent area of high pressure at the surface and aloft will remain over the eastern CONUS through the upcoming weekend. Low pressure is likely to track west of the state early next week with a trailing cold front and potent upper level disturbance pushing through Pennsylvania Tuesday or Tuesday night preceded and accompanied by periods of rain and perhaps a narrow band of gusty thunderstorms Tuesday afternoon and evening. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... An area of mainly thin high clouds are masking a sct-bkn layer of stratocu clouds over portions of the central and western mountains of PA. An ill-defined surface frontal boundary (depicted almost solely by a 6-10F Dewpoint drop) will slide SE from the Lower Great Lakes and dissolve across northern PA during the day today. As a result of the clouds and light westerly wind, the temp drop had been trimmed with 08Z readings in the low-mid 50s across the Central Mtns and Laurel Highlands, while areas outside of the veil of high clouds streaming SE across the region, have dipped into the 40s. Current cloud cover, wind and T/Td spreads will support at best, Patchy River Valley Fog for 3-4 hours this morning. The area of high clouds shifts SE of the region by late this morning and any cloud cover for the bulk of the late morning and afternoon hours should be limited to few-sct, high-based flat cu or altocu as slight cooling in the mid levels occurs with a minor bump up in the mean 850-700 mb RH values. Min temps around sunrise today will range through the 40s across the Northern Mtns and throughout the Susq River Valley, to the lower 50s across the Central Mtns and hilltops near the Mason/Dixon line. 925mb temps of around 14C will combine with the abundant sunshine and low dewpoints to yield afternoon max temps in the upper 60s across much of the NW half of the CWA, and low 70s across the Susq Valley and southern tier of PA. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Strong upper ridge expands northward from the Ohio Valley tonight with the center of a 1024mb sfc high sliding across Central PA. Light wind and clear skies will allow temps to dip into the 40s in practically all locations, though some of the perennial cold rural valleys across the Central and Northern Mtns could dip into the upper 30s with patchy valley for a few hours around daybreak. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Latest ECENS and NAEFS maintain an anomalous upper level ridge over the area through the weekend. This should ensure fair weather with above average temperatures Saturday to Sunday. Ensemble mean 925/850 temps support highs of 70-75F, while light wind and dry air result in seasonably cool nights. Some of the normally warmer locations in southern PA, resulting from enhanced downslope/adiabatic warming of a southerly llvl flow could nose up to 76-77F. All medium range guidance indicates that there will be a significant digging northern stream trough that will eventually take on a slightly negative tilt early next week as it moves from the upper midwest and Miss Valley to the Appalachian Mtns and Carolina Coast. Models have converged to indicate the center of the significant rainfall event occurring late Monday through tuesday evening when widespread rainfall amounts of 1-1.5 inches is anticipated. As the cold front pushes east through the commonwealth Tuesday into Tuesday evening, Sfc-850 mb Lifted Indices go slightly Negative acrs parts of Scent PA and the Susq Valley. Pattern appears favorable for a Narrow Cold Frontal Rainband - NCFRB (with brief gusty winds) to push through the expansive shield of moderate to briefly heavy rainfall rates. Current forecast rainfall amounts pose little threat for any small stream flooding considering much higher short term FFG values. A period of near to below normal temperatures appears likely for the second half of next week, as upper trough swings east into the area. However, both GFS and ECMWF ensemble systems indicate the thrust of the chilly air will be directed west of Pa and there are indications of rising heights/milder weather across the entire eastern conus toward the end of the month. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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Current GOES-16 shows back edge of cirrus over northern PA, revealing valley fog. KBFD was temporarily impacted by vis restriction but trends suggest prevailing VFR. Overall, VFR remains the prevailing flight category with low confidence for terminal impacts in late-night/early morning valley fog. Outlook... Sat-Sun...Patchy AM valley fog otherwise VFR. Mon-Tue...VFR to MVFR/IFR. Showers likely; periods of heavy rain and gusty winds possible with strong FROPA. LLWS. Wed...Breezy. Sct showers. MVFR NW 1/2.
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&& .CLIMATE... Month-to-date, October 2017 is the warmest October on record at Harrisburg and Williamsport. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/Ceru AVIATION...Steinbugl CLIMATE...Steinbugl

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