Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 221854 AFDCTP Area Forecast Discussion National Weather Service State College PA 254 PM EDT Sun Oct 22 2017 .SYNOPSIS... A large area of high pressure centered off the New Jersey coast will bring spectacular Autumn conditions today through much of Monday, to enjoy the near peak color of the fall foliage. A high-amplitude and deepening, cold upper trough will become located across the eastern U.S. during the Wednesday and Thursday timeframe. This weather feature will be preceded and accompanied by rain that could be heavy at times late Monday into Tuesday. There is also a chance that a narrow band of gusty thunderstorms will develop and push east across the state along a cold front during the day Tuesday. Brisk and colder weather will follow for Wednesday afternoon through Thursday with the likelihood of the first snowflakes of the season across the Northern and Western Mountains of Pennsylvania. && .NEAR TERM /THROUGH TONIGHT/... Sunny skies with only some mid clouds and cirrus continues across the region. These clouds will stifle max temps so expect them to be in the mid 70s this afternoon. Skies will slowly cloud from east to west overnight as mid level upslope flow brings low clouds to the region by overnight. These clouds will keep overnight lows warmer then previous, with lows in the low to mid 50s, which is 10 to 20 degrees above normal. && .SHORT TERM /MONDAY/... An upper level trough low swinging through the upper midwest will absorb a closed upper low over the lower Mississippi valley during the day Monday. This will bring an extensive plume of moisture into the state from the south. The south to Serly llvl flow will freshen by about 10 kts during the day Monday and bring with it areas of low clouds (stratus/Stratocu) and perhaps some patchy drizzle across the central third of the state. Max temps Monday should be about 3-4 F lower than those of today for everyone except those in the Lower Susq Valley. Short to mid range models continue to narrow in on the timing of the approaching system. 12Z GEFS and NAM are in fair agreement on precipitation reaching Western PA and the Alleghenies late tomorrow afternoon. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Models have converged to indicate the center of the significant rainfall event occurring later Monday night through Tuesday evening when widespread rainfall amounts of 1-1.5 inches is anticipated. As the cold front works slowly east across the Commonwealth Tuesday into Tuesday evening, SFC-850 mb LIs go slightly negative across parts of south central PA and the Susquehanna Valley. In addition to the expansive shield of moderate to briefly heavy rainfall rates, the pattern appears favorable for a Narrow Cold Frontal Rainband - NCFRB (with brief gusty winds) to push through as well. By Thursday, 850 mb temps drop below zero which will bring a relatively chilly day with scattered rain showers which may mix with a snowflake or two over the higher elevations. However, this cooler stretch will be short lived as heights and 850 temps rise quickly into next weekend. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... Guidance continues to show risk for low clouds and fog developing late tonight into early Monday morning across the eastern 1/3 of the airspace - and have increased and spread MVFR/IFR restrictions through the eastern and central TAF sites. Have kept restrictions until around 14Z. LLWS is possible at JST/AOO and BFD but it is marginal as strongest low level jet is above 2KFT. So have left it out of the TAFs for now. Outlook... Mon...AM low cigs/fog possible eastern 1/3. Showers advancing into the airspace Monday night with lowering cigs/vis and LLWS. Tue...LLWS/gusty/heavy showers in the morning. Sharp FROPA and windshift. Improving conditions by afternoon. Wed-Thu...Sct showers and low cigs possible KBFD/KJST. && .CLIMATE... Month-to-date, October 2017 remains the warmest October on record at Harrisburg and Williamsport. Despite very warm days, seasonably cool nights and calender length has been putting a dent in the avg. monthly temperature at both sites. The top spot is in jeopardy given upcoming pattern change/cool down expected by midweek. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert/Ceru SHORT TERM...Lambert LONG TERM...Lambert/Tyburski AVIATION...Ceru/Steinbugl CLIMATE...

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