Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 230910 AFDCTP Area Forecast Discussion National Weather Service State College PA 510 AM EDT Mon Oct 23 2017 .SYNOPSIS... 1008 MB sfc low over the confluence of the Ohio and Mississippi Rivers will track northward through the Great Lakes late today and Tuesday. A trailing cold front will push northeast through Pennsylvania late today and tonight. An upper level trough will then swing through Pennsylvania Wednesday and Thursday bringing notably cooler temps and some snow showers across the NW mtns and Laurel Highlands of the state that could coat the ridge tops Wednesday night. Temperatures will recover to near or slightly above normal for Friday and Saturday before another deepening trough in the northern stream brings the coldest air of the Fall Season with a likelihood of a widespread moderate rainfall event in the east, with mixed precipitation or snow falling across the Western half of the state the last several days of the month. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Sharp ridging at the surface and aloft will slide off the East Coast today, allowing a potent southern stream closed low to lift quickly NE through the Tenn and Ohio Valleys before reaching the Alleghenies of Wrn PA and WVA later this evening. Plenty of thick cirrostratus with some Alto Cu will be present for much of today, while an area of low stratus over the Susq Valley and western Poconos advecting/expanding to the north and west throughout the day. These persistent and thick lower clouds prompted me to undercut most model guidance max temps for today by some 5-10 deg F. Highs should range from the upper 50s and lower 60s across the central and western mtns, to between 65-70F in the SE part of our CWA. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Cold front is progged to push slowly east across the Commonwealth tonight into early Tuesday. Models showing a fair amount of instability (in the form of sfc-based cape between 500-700 j/kg) just ahead of the front across the far eastern part of our CWA (namely Lancaster and Lebanon counties tonight). Strong, southerly LLJ of 55 to 65 kts at 850 mb will descend a bit and combine the cfropa to trigger enhancement of the line as it moves across our far eastern CWA. SPC`s Day 1 MRGL Risk for SVR noses into our far SE zones. The high shear/low cape environment will persist tonight to the east of the Susq Mainstem as the front grinds slowly to the east. This will likely result in a few embedded tsra, or more likely a NCFRB with brief, strong to isolated damaging straight-line gusts in excess of 45 mph. This favorable low cape/high-shear environment could lead to some isolated instances of wind damage. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Surface ridging indicated over central Pa by med range guidance late Tuesday through Friday, indicating dry weather for most of the forecast area. The exception will be late Wed, when passage of shortwave could produce a few showers across the northwest mountains. Ensemble mean 925/850 temps are slightly below normal Wed/Thu, likely translating to max temps from the upper 40s over the Alleghenies, to the upper 50s across the southeast counties. This cooler stretch will be short lived as heights and 850 temps rise quickly into next weekend. Another chance for precipitation will arrive at the end of the period when a cold front is anticipated next Sunday, bringing rain to much of the CWA, while colder air and a few waves of low pressure riding NNW along the front brings the chance of a light to moderate, and elevation dependent snow event. && .AVIATION /09Z MONDAY THROUGH FRIDAY/... After a prolonged period of largely unrestrictive/VFR flying conditions, the weather is about to become rather tumultuous over the next 24 to 36 hours. A steady does of thickening high clouds will continue to blanket the airspace. Beneath the cirrus canopy, a moist east-southeast flow will result in MVFR/IFR conditions this morning over the east-central airspace. High confidence at the southeast airfields KLNS/KMDT based on current satellite, observational and guidance trends. Not totally convinced in significant improvement during the day at the eastern TAFs and have hedged toward the low end of the guidance spread which keeps MVFR cigs through the afternoon/eve. Winds from 140-180 degrees will increase through the period with surface gusts 20-30kts this evening into tonight. LLWS is expected tonight as low level jet reaches 50+kts ahead of cold front pushing east across the airspace. A band of moderate to heavy rain is likely along the front late tonight into early Tuesday morning and may be accompanied by strong, gusty winds or embedded thunderstorms. Models are in good agreement in shifting the frontal rain band east of the airspace after 24/12-15UTC with rapidly improving conditions to VFR by Tuesday afternoon. Outlook... Wed-Thu...Sct showers/low cigs possible especially KBFD/KJST. Fri...Mainly VFR with chance of showers wrn 1/2 Fri night. && .CLIMATE... Through 10/22/17, the average monthly temperatures at Harrisburg and Williamsport are 63.8F and 61.8F. When compared to the maximum 1-month mean avg. temperature for previous Octobers, both would rank as the warmest on record. Computing a daily avg. temperature when only taking into account the first 22 days of the month and comparing to the previous Octobers, the rankings are #2 at IPT and #3 at MDT. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Fitzgerald/Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/Gartner AVIATION...Steinbugl CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.