Area Forecast Discussion
Issued by NWS State College, PA

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900 FXUS61 KCTP 210354 AFDCTP Area Forecast Discussion National Weather Service State College PA 1154 PM EDT Sun May 20 2018 .SYNOPSIS... A weak cold front will settle south of the area by this evening followed by drier air that will finally work into the region. During the day Monday, this same old frontal boundary will lift back northward as a warm front. Showers and scattered thunderstorms will accompany the front as it lifts north across the Commonwealth. Most of the showers and storms will be from late Monday into early Wednesday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Current fcst on track. Earlier discussion below. Showers and storms south of PA as of 520 PM. Updated the grids. Afternoon discussion below. Satellite shows brightening skies, but with plenty of post frontal strato-cu over northern areas. The HRRR doesn`t make me optimistic for these clouds to mix out in time to bring much sunshine before the afternoon is over. Over the SE, still ahead of the weak front, a few showers are developing. They are still fairly squat and despite the RAP showing max CAPEs in excess of 1000J, lapse rates are not very impressive so we expect little more than some brief showers and maybe a rumble of thunder. The HRRR shuts things down fairly quickly after about 5PM. High pressure over the Upper Midwest/Northern Great Lakes will build SE and moves across Pennsylvania late tonight and Monday morning with fair/dry weather, lower humidity and light wind helping to yield cool temps. Recent rains have left conditions moist, so some late night fog looks like a fair bet. Lows tonight will vary from the upper 40s across the Northern Tier of PA to the lower 60s in the Southern Valleys. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... The gift that keeps on giving in the form of our cold front, will start to make a return Monday as a warm front. The first showers could reach my SWRN Laurel Highlands zones by mid day, but more likely we will see the chance for showers ramp up from SW to NE as the afternoon progresses. Ensembles show the PWATs starting to creep up and 12Z guidance shows some erosion in the stability, so thunderstorms will be possible. Highs should be relatively pleasant topping 70 everywhere. That`s a few degrees warmer than normal for the time of year. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... After being suppressed to our south early next week, the chances for convection will increase once again Monday afternoon and especially Monday night into Tuesday as moisture on the northern periphery of the subtropical ridge creeps back into the region as an old frontal boundary lifts to the NE as a warm front, putting the west into the warn sector. Numerous showers along with a few thunderstorms will bring a few to several tenths of an inch of rainfall to much of the region Monday night into Tuesday before drier air makes a push in from the NW behind a weak cold front starting Wednesday. Tuesday looks like the coolest day of the week, though humidity will be highest. From there it looks like the period form Wednesday through Friday will feature some rare (of late) rain-free conditions, before the chance for a pop-up shower or storm becomes returns for Sat. Temps look to climb into the 70s each day, with Saturday the warmest as high range from the mid 70s to the lower 80s. The coolest morning will be Friday with valleys of the northern mountains dipping into the mid 40s. More active weather returns for late weekend as another period of showers and scattered thunderstorms begins. && .AVIATION /04Z MONDAY THROUGH FRIDAY/... Clearing skies, a diminishing wind and wet ground will likely lead to areas of valley fog late tonight. The weakest pressure gradient and lightest winds should be across the northern tier, where SREF prob charts and NAMnest indicate the most widespread vis reductions late tonight. However, patchy fog is possible even into southern Pa late tonight. The one airfield least susceptible to radiation fog will be KJST, due to its ridgetop location. Any fog should mix out between 12Z-14Z. After that, there is some concern of MVFR cigs in the vicinity of KJST/KAOO later Monday, due to a developing easterly flow ascending the higher terrain of south central Pa. Based on an examination of varying model guidance, believe the odds of this are slightly less than 50 pct. Much drier air working into northern Pa should ensure VFR conditions across that part of the state Monday. Outlook... Tue...AM rain/low cigs possible. PM tsra impacts possible west. Wed...AM low cigs possible W Mtns. Thu-Fri...No sig wx expected. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte/Martin NEAR TERM...La Corte/Martin SHORT TERM...La Corte LONG TERM...RXR AVIATION...Fitzgerald

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