Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 171014 AFDCTP Area Forecast Discussion National Weather Service State College PA 614 AM EDT Mon Jul 17 2017 .SYNOPSIS... A very weak cold front sliding slowly through northwestern Pennsylvania today will combine with a lead surface trough forming over the Susquehanna River Valley this afternoon to bring numerous showers along with isolated to scattered, strong to severe thunderstorms over the eastern half of the state this afternoon and evening. Partial clearing, light wind and moist ground from todays showers will lead to areas of fog, especially across central and northern Pennsylvania. The weak front will stall out across southern and eastern Pennsylvania tonight and Tuesday triggering another round of scattered showers and thunderstorms Tuesday afternoon and early Tuesday evening. Slightly drier air and lesser chances for showers will occur across the northwest mountains of the state on Tuesday as a weak area of high pressure build in. Wednesday and Thursday looks to be mainly dry with moderately high daytime humidity and temperatures running a few to several degrees above normal. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A weak...1013 mb sfc low was located over eastern Lake Erie and dragging its trailing cfront slowly to the east. Across much of central and eastern PA, a relatively light, 10-15 kt southerly boundary layer flow will help to increase PWAT values from their present 1-1.5 inch values, to between 1.5-2.0 inches across the SE half of the state late this afternoon and evening. This abundant moisture will pool near and to the east of a gradually sharpening lee trough across the Central Mtns and Susq Valley, and we expect to see scattered- numerous moderate to briefly heavy rainshowers and isolated to scattered strong TSRA across central PA, with a few SVR TSRA possible near and to the east of the Susq Valley where the best low-level theta E convergence will be found, coupled with MU capes of 2000-3000 j/kg. Pulse and multicell clusters are the primary severe weather type expected, though some of the stronger updrafts could exhibit transient mesos and some instances of large hail over 1 inch in diameter. SPC has several counties in our NE CWA within a slight risk for severe thunderstorms today, with a marginal risk for most of the rest of the area (except for Warren county, where a mid to late morning cfropa will occur). High temps today will vary from the u70s across the northern and western mtns...to the mid and upper 80s across the Susq Valley. Will have to closely monitor the region between KUNV...KIPT and KMDT for the potential of locally very heavy rain and Flash Flooding where the slowing/dying cfront and lee trough merge late today and early tonight. 3 hour FFG values are lowest in our CWA there and generally between 1.5-2 inches. WPC`s Day 1 Excessive Rain Outlook paints a marginal risk across the Central Mtns and Susq Valley with a Slight Risk across the Middle Susq Valley northeast to the Wyoming Valley (KAVP). && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... The frontal boundary drifts slowly east across the Central mtns through tonight, weakens further and blends in with the Lee Trough across the Susq Valley and Scent PA. This will leave the chc for isolated to scattered SHRA lingering through the night. Also included areas of fog after midnight, as partial clearing is expected - at least across the NW half of the CWA, along with near calm air, dewpoints in the 60s and wet ground in many locations. Low temps at daybreak Tuesday will range from the mid to upper 50s over the NW mtns, to near 70F in the SE metro areas. The lingering llvl boundary across the SE half of PA will bring a delay to sweeping away the mugginess that will form in that region Monday. Scattered mainly afternoon showers and thunderstorms will form once again, while a weak bubble of high pressure brings a light west to NW breeze and a much lesser chc for precip (along with more comfortable dewpoints in the u50s to L60s). Tuesday`s high temps will be about 2-3F higher than Monday`s. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... An upper level trough should be moving east of the area very early in the long range period. However, the timing is slightly in question for when to make the forecast mostly dry. The upper flow is characterized by a persistent WNW flow due to weak troughing over ern Canada and a flat, broad ridge over the Srn/SErn states through almost the entire period. This puts the region at risk for some convection almost every day - mainly from either diurnal convection or dying MCSs. But, the mean steering current lends itself to just slightly below normal POPs on the whole. The driest time in the extended appears to be Wednesday through midday Thursday. A fairly potent trough moves in/through around Thursday/Night periods and have made POPs inch into the 60s in the NW, but held them in CHCs everywhere else. The first half of the weekend (Fri/Sat) could be dry, but low CHC POPs still probably the best bet then with the timing of individual MCSs and short waves a folly at this range in such a fast, almost zonal, flow. Consensus forecast then increases POPs again later in the weekend. The PWATs never really get too far from normals. The 8H temps also waggle only 2-4C through the period - hanging in the 15-18C range. The upper ridge to the south should help us to stay at or above normal temps through the long range. Thus, maxes should run mainly u80s-l90s in the SE and u70s-l80s in the NW. && .AVIATION /10Z MONDAY THROUGH FRIDAY/...
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Nothing much on the radar now. Some fog here and there. 09Z TAFS sent. Earlier discussion below. Some strong storms over the lower Great Lakes, but nothing much in our area. High pressure drifts east as a cold front slowly edges in from the west today. The front is showing up as a broken line of showers/isolated thunderstorms that will erode as they push slowly eastward. Though a shower can`t be ruled out at KBFD overnight. VFR conditions will be the rule however, except for some isolated valley fog. The return of more humid conditions on Monday as the front meanders across central PA will bring increasing likelihood of showers and thunderstorms - especially across the eastern half of CWA where some storms could become strong to severe in the late afternoon. The front pushes east of the region by Tuesday with drier weather and good flying conditions. .OUTLOOK... Tue...Sct tsra impacts poss east. Wed...No sig wx. Thu-Fri...Sct tsra impacts, esp NW.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Ross/Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Dangelo/Lambert AVIATION...Martin

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