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Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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483 FXUS61 KCTP 281507 AFDCTP Area Forecast Discussion National Weather Service State College PA 1107 AM EDT Fri Jun 28 2024 .SYNOPSIS... *Seasonably warm and pleasant today; increasing clouds tonight *Heat and humidity spike fuels severe T-storm risk this weekend *Refreshing/dry start to July; heat+T-storms return by the 4th && .NEAR TERM /UNTIL 8 PM THIS EVENING/... Mostly sunny to partly cloudy and pleasant wx conditions across central PA for the last Friday of June. Highs temperatures this afternoon will range from 75-85F which is quite seasonable for this time of year or within +/- 2 to 4 degrees of the historical average for late June. && .SHORT TERM /8 PM THIS EVENING THROUGH SATURDAY NIGHT/... GEFS and NBM indicates an increasing/anomalously strong south/SSW llvl return flow developing for later tonight through Saturday with the anomaly of the LLVL v-component reaching around plus 3 sigma across northern PA and a solid 2+ sigma elsewhere across Central and Southern PA Saturday afternoon and evening. Latest model data suggests 30-40kt LLJ from the south- southwest will drive some showers and elevated t-storms over west central PA later tonight into early Saturday morning. This strong vertical speed and directional shear coupled with increasing meso-B lift associated with the Right Entrance region of a 100+ KT jet to our north will support the likelihood of another fairly widespread strong to severe convective events with a distinct threat for isolated tornadoes with discrete cells, BKN-S signatures that are accompanied by a near perpendicular deep layer shear component to their long axis. SPC not only expanded the SLGT risk across all but our far SE CWA, but also introduced a 5% TOR threat across roughly the NW 40 percent of PA. 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 2-2.5 inches on Saturday or +2-3SD. The anomalous, deep-layer moisture will support risk of heavy to potentially excessive rainfall with point amounts of 3 inches possible in places experiencing multiple TSRA. WPC has maintained 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 influence of early day clouds/waning overnight convection could be a key/limiting factor. The mid level cap is similar in strength to our past SVR event this past Wednesday with 700 mb temps in the 8-9.5C range and weak broad scale forcing until the afternoon/evening arrival of the better omega field beneath the favorable RR Quad of the aforementioned ULVL jet. Convection should decrease in coverage and intensity into Saturday night, which will be warm and muggy with lows 65-75. && .LONG TERM /SUNDAY 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 /15Z FRIDAY THROUGH TUESDAY/... VFR conds will prevail through Friday with primarily high cirrus and fair weather cu expected. The exception will be patchy valley fog in the northern Alleghenies early this morning. Winds will start the day light and variable, then veer to become S to SE later in the day on Friday with gusts generally less than 20 kts. As a warm front approaches late Fri night into Saturday, southeast flow will bring increasing moisture and the potential for low stratus across southern and eastern PA. Confidence is relatively high in restrictions after 06z Sat for airfields from UNV eastward, with a 25-50 percent chance of IFR conditions at MDT and LNS. Overnight rain and some thunder is possible especially in the north, mainly after 06z. Some marginal LLWS is also possible mainly in the north. The low stratus is expected to lift and become broken to scattered before more numerous showers and thunderstorms develop later on Saturday. The chance for showers and storms will linger across the southeast into Sunday as a cold front swings through the area. Outlook... Mon-Tue...Dry weather with VFR conditions. && .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...Steinbugl NEAR TERM...Steinbugl SHORT TERM...Lambert/Steinbugl LONG TERM...Jurewicz/Steinbugl AVIATION...Martin/Colbert CLIMATE...Steinbugl