Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 212002 AFDCTP Area Forecast Discussion National Weather Service State College PA 402 PM EDT Wed Jun 21 2017 .SYNOPSIS... An upper air disturbance will will push southeast across the region this afternoon. A deep upper level trough will approach the region bringing increasing humidity along with the chance for showers and thunderstorms late Thursday into Saturday. Drier and cooler conditions will return later in the weekend into next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Radar shows a broken line of showers and thunderstorm from around SEG west to around JST. The HRRR keeps the activity mainly south of I-80 for the remainder of the day. While moisture is not abundant, moderate instability and shear are in place ahead of an approaching shortwave and upper jet streak. Forecast model soundings show a nice inverted V signature for this afternoon. SPC has painted much of the CWA with a Marginal Risk for severe storms. While the updrafts thus far have not been especially robust, this looks reasonable given the instability/shear and expected lift under the left exit region of the upper level jet. Relatively high convective LCLs/cloud bases will help to produce isolated and brief, strong downburst winds through late afternoon. Basin average rainfall today should stay under 0.20 of an inch. A push of lower PWAT air in the wake of this sfc/upper level disturbance should result in drying over NW PA and the remainder of the forecast area as we get into the overnight. Temperatures will fall into the 40s over the north and range to around 60 over the SE. This expected cooling down near the dewpoint in most areas should equate to areas of fog late at night, especially in the valleys and areas where it rains over the next few hours. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... Thursday will start out partly cloudy and comfortable with the patchy early fog as a bubble of high pressure slides SE and over us for late morning. The low level flow will strengthen from the SW during the afternoon bringing in noticeably more humid air along with an increasing chance of an afternoon or evening shower or thunderstorm. PWATs will increase from below normal (only 15-20 mm this morning) to over 40 mm (or 1-2 sigma) by 00Z Friday just to the west of the approaching warm front. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
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From a large scale perspective, the medium range forecast will feature a seasonably strong/amplified upper trough settling over the Northeast U.S into next week. Expect moisture/rainfall associated with the remnants of TS Cindy to exit the area by the start of the weekend. Confidence is low with details (timing) with multiple shortwaves reflecting surface fronts/troughs inducing risk for isolated to scattered showers and Tstorms Mon-Wed. By Friday the tropical airmass will have re-established itself with dewpoints well up into the 60s and lower 70s over the entire region making for a sticky end of the work week. Model consensus continues to signal rain on Friday/Friday night corresponding with a peak in H85 moisture flux and PW. The heaviest rain is fcst to stay to the south of PA. Drier, low PW air arrives by early Saturday and lasts through the weekend. This should translate into comfortable, low- humidity conditions with temperatures near to slightly below late June climatology. Precipitation opportunities will be modulated by several shortwave impulses which have low predictability at this range. Any rains would be generally scattered and on the lighter side given overall lack of deep layer moisture. 21/12z GEFS shows PW values remaining below average into midweek. Temperatures should stay on the cooler side of climo through midweek as the upper level trough shifts east of the area. FWIW the GFS is more bullish vs. EC on heights rebounding/building SE U.S. upper ridging into the second half of next week. That said, there is general agreement in a modest warming trend later next week as the trough moves out and heights return to normal.
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&& .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... VFR conditions will continue into the evening hours. An approaching upper level disturbance is triggering scattered showers and thunderstorms. Some of the stronger storms will cause brief localized sub VFR conditions, and could also cause strong wind gusts, mainly this afternoon. The wind will become SW picking up to around 10 mph gusting to 15-20 mph. Any convection will down pretty quickly by early evening, and initially mainly clear skies and quickly diminishing wind will likely lead to areas of valley fog during the overnight hours (mainly where rain falls today). A warm front will approach the region Thursday triggering showers and scattered thunderstorms, mainly over the west and NW during the afternoon. .OUTLOOK... Fri...Widespread sub VFR likely with rain and embedded thunderstorms. Sat-Sun...Mainly VFR Mon...Mainly VFR. Chc SHRA/TSRA. && .EQUIPMENT...
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KCCX radar will be offline for approximately 4 days starting Saturday, June 24th for technicians to install the first of 4 major service-life extension upgrades. The work on the radar has been scheduled to minimize potential impacts to operations and will be delayed if hazardous weather is forecast.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...La Corte LONG TERM...Steinbugl AVIATION...La Corte EQUIPMENT...Steinbugl

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