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Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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559 FXUS61 KCTP 280249 AFDCTP Area Forecast Discussion National Weather Service State College PA 1049 PM EDT Thu Jun 27 2024 .SYNOPSIS... *Seasonable end to the week with comfortable humidity *Return of heat+humidity fuels T-storms this weekend *Cooler & dry start to July; heat & T-storms by the 4th && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 645 pm update... The diurnal cumulus field is fading fast this evening with the loss of daytime heating in a dry air mass. This will lead to a clear and refreshingly cool night for late June. As indicated in the previous discussion, good radiational cooling conditions overnight should lead to the development of river valley fog, especially across northern PA and across the Alleghenies. Lows by daybreak will range from the mid 40s across the northern tier, to the upper 50s over portions of south- central PA. Previous discussion... Cu will crumble this evening setting up a refreshingly cool and mainly clear night across central PA. Low pwats and favorable radiational cooling pattern supports trending below the 50th percentile NBM with relatively chilly min temps in the mid 40s across the northern tier. Beneath dome of 1020mb high pressure, synoptic conditions support fog formation late tonight into early Friday morning in the river/stream valleys across the western and northern Alleghenies. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... AM fog will dissipate quickly after sunrise Friday. Expect partly cloudy and seasonably comfortable conditions with highs 75-85F. An increasingly strong southerly llvl return flow develops into Friday night as the aforementioned surface high shifts eastward off the New England coast. Latest model data suggests 30-40kt LLJ from the south-southwest will drive some showers and elevated t-storms over west central PA late Friday night into early Saturday morning. The belt of strong 850mb flow will transport rich low level moisture (dewpoints in the upper 60s to lower 70s) northeastward along/ahead of a cold front this weekend. PWAT values are forecast to reach 1.5-2.5 inches on Saturday or +2-3SD. The anomalous deep layer moisture will support risk of heavy to potentially excessive rainfall. WPC currently has a broad MRGL risk, but the setup will likely yield an upgrade to SLGT risk particularly where FFGs are reduced. Although mid lvl lapse rates may remain weak, high dewpoints and diurnal heating should fuel at least moderate buoyancy by mid/late afternoon. The projected instability and deep shear profiles support a conditional risk of strong to severe storms. SPC has most of the area in a MRGL risk for D3, but their discussion suggests a categorical upgrade/expansion of SLGT risk (just to the west) is possible in subsequent outlooks. The influence of early day clouds/waning overnight convection could be a limiting factor. Convection should decrease in coverage and intensity into Saturday night, which will be warm and muggy with lows 65-75. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... On the large-scale, a fairly zonal upper-level flow pattern will stay in tact over the northern tier of states next week, with energetic short-waves traversing this flow every 3-4 days or so. Consequently, expansive summertime upper ridging will largely stay south of PA, keeping excessive heat mainly out of the forecast for the time being. Looking at the daily sensible weather, as one of the above mentioned short-waves presses through eastern Canada and New England early next week, it will push a surface cold front well to the southeast of the Commonwealth, bringing another stretch of dry conditions and comfortable temperatures/humidity levels for Monday and Tuesday. Confidence in this scenario is relatively high. By the middle of next week, as a surface high pushes offshore and heights aloft begin to build, summertime heat and humidity should at least temporarily make a run at PA. At the same time, though, the next upstream surface cold front and upper-level trough will be approaching from the northwest. The most likely scenario here is for increasingly muggy conditions and higher chances for showers and thunderstorms. Just how hot temperatures are able to get, or robust convection becomes, is fairly uncertain. Better knowledge of these factors will require considerably more time and additional model runs to see how atmospheric features resolve themselves during this time frame. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... Late evening update. Main change was to adjust winds to the north, based on current obs and guidance. Earlier discussion below. For the 00Z TAF package, looking at mainly clear skies overnight, as high pressure builds into the area. As I mentioned on the late afternoon update, I added a TEMPO group for fog at BFD late, as low temperatures drop to or just below the expected dewpoint. Friday looks like a dry day at this point, with a southerly flow of air and just a few clouds. More in the way of adverse weather for the weekend, as a warm front lifts northward, followed by a cold front on Sunday. Outlook... Sat-Sun...Widespread showers and thunderstorm with impacts possible. Mon-Tue...Dry weather with VFR conditions. && .CLIMATE... Through 6/26, June ranks as tied for the second warmest on record at Harrisburg. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Steinbugl NEAR TERM...Jurewicz/Steinbugl SHORT TERM...Steinbugl LONG TERM...Jurewicz/Steinbugl AVIATION...Martin CLIMATE...Steinbugl