Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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880 FXUS61 KCTP 300318 AFDCTP Area Forecast Discussion National Weather Service State College PA 1118 PM EDT Sat Jun 29 2024 .SYNOPSIS... A cold front will push through central Pennsylvania on Sunday. A large high pressure system will build into the region early in the upcoming week, followed by a dying cold front pushing in from the Great Lakes and stalling out over the area late next week by the middle of next week. && .NEAR TERM /THROUGH SUNDAY/... Lingering convection over parts of the south central and southeast late this evening should continue to decrease in coverage after midnight. Can`t drop POPs altogether overnight as 850 mb thermal ridge is overhead and additional isolated showers can still pop up overnight, but most areas will remain dry. We expect there to be areas of fog give current dewpoint depressions of 1-3F and dewpoints in the lower 70s. Some areas of fog are very likely given high surface dewpoints and light winds ahead of the cold front that will be approaching from the GLAKS and Ohio Valley overnight. With thermal trough in place and 850 temps around +18 to +19 across much of central PA, lows tonight will be warm, ranging from the mid 60s to mid 70s, which is 10 to 15 deg F above normal for late June. && .SHORT TERM /SUNDAY NIGHT THROUGH 6 PM SUNDAY/... Passage upstream surface cold front will bring the chance for another round of convection Sunday. Locations most likely to see potential strong/svr t-storms are over the southeastern part of the CWA due to a fropa coinciding with peak heating of the late afternoon. Max temps Sunday will be a few to several deg F higher than today (Sat) in all locations. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... Dewpoints drop off rapidly by Sunday evening with another comfortable few days of weather in store to start the month of July. Canadian high pressure builds to southern Ontario by Monday night, bringing a fair and cool night with the high moving directly overhead. This will result in efficient radiational cooling and min temps several degrees below normal. Fair and warmer weather is expected Tuesday into at least the first half of Wednesday, as upper level ridging builds over the state and surface high drifts offshore. All medium range guidance tracks a weakening shortwave well north of PA late Wednesday into Thursday. The dying cold front is likely to sag into the state Thursday and stall out in the vicinity of PA through Friday. Falling heights/surging low level moisture ahead of the front could support scattered convection as early as Wednesday afternoon over the northwest half of PA. However, a better chance of showers/tsra areawide will come with the arrival of the front Thu into Friday. Early best guess of late week rainfall based on ensemble plumes ranges from 0.25 to 0.75 inches, with the highest amounts over the N Mtns and least in the south. Heat and humidity should peak ahead of the front Wed-Thu. Ensemble mean 850mb temps surging to near 20C indicate max temps could reach the low to perhaps mid 90s in the Lower Susq Valley Thursday, with high humidity pushing heat indices into the mid and upper 90s. Ensemble plumes suggest slightly cooler daytime temps late week, due to more clouds/showers. However, high pwats in the vicinity of the stalling front should result in muggy nights and above normal min temps the entire second half of next week. Models begin to diverge as we head into the weekend. Most guidance suggests that rain chances stick around through at least Saturday as another cold front approaches the area. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... A few more adjustments made just before I sent the 00 TAF package. Main thing was to add in some VCSH early on, as the airmass is supporting a few showers forming since about an hour ago. Earlier discussion below. Adjusted TAFS several times this afternoon and early this evening, as line of storms that formed over the mountains earlier this afternoon have been moving along at a rather fast pace. Still concern that the far southeast activity may slow some, given the southeast flow and very high dewpoints in place now. Main change to the 00Z TAF package was to back off on showers overnight, and put showers in toward Sunday morning, given location of main cold front and upper level forcing. Still expect conditions to improve later Sunday, as the winds shift to the northwest and much less humid air moves into the area from northwest to southeast. Monday and Tuesday look dry at this point with a dry airmass and VFR conditions, as high pressure builds into the area. A bit breezy on Monday, given the cooler air being advected into the region. Outlook... Mon-Tue...Dry weather with VFR conditions except perhaps some AM valley fog N. Wed...PM TSRA moving across from W-E. Thu...A chance of showers and storms. && .HYDROLOGY... Over half of an inch of rain last night and this morning over the far NW has increased confidence that the precip in the N will be very efficient today. While dbZ and the amt of ltg may not impress today, the moist adibatic profiles and deep warm layer will make for heavy rain at times. Draw back to fast storm motions: 1) radar may underestimate precip as the fast cells skip along in between scans, and 2) it`s tough to get flooding when the cells have a low residence time. However the repeated showers/storms could (easily) overcome that issue. Prev... The area of greatest concern for heavy rain and flash flooding will spread south and east later this morning through this afternoon as the axis of the LLJ slides east and the favorable RR quad of an approx 2 sigma upper level jet and its enhanced MESO-B lift moves overhead. PWAT values increased steadily from west to east overnight from a little over one inch to start the night to around 1.6 inches early today. PWATS via the GEFS will peak around +3 sigma or about 2.25 inches later this morning through this afternoon (which are values that haven`t been seen so far in PA during 2024). This anomalous, deep moisture will support the threat for locally very heavy rain (in excess of 2 inches/hour) within a broad area of 1 to 1.5 inch basin average storm total rain forecast for much of Central and Northern PA. Issued a Flood Watch from 12Z today through 06Z Sunday for much of Central and Northern PA where FFG values are well under 2 inches/3 hours across parts of the Northern Mtns. && .CLIMATE... Through 6/27, June ranks as the second warmest on record at Harrisburg with an average monthly temperature of 76 degrees or +3.8 degrees above normal. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert/DeVoir/Fitzgerald NEAR TERM...Lambert/DeVoir/Fitzgerald/Dangelo/Martin SHORT TERM...DeVoir/Fitzgerald/Steinbugl LONG TERM...DeVoir/Fitzgerald/Bauco AVIATION...Martin HYDROLOGY...Lambert/Dangelo CLIMATE...Steinbugl