Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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512 FXUS61 KCTP 280928 AFDCTP Area Forecast Discussion National Weather Service State College PA 528 AM EDT Fri Jun 28 2024 .SYNOPSIS... Seasonable temperatures and comfortable humidity will close out this workweek. Strengthening south to southwesterly winds through a deep layer of the atmosphere will transport increasing heat and humidity for Saturday and help to fuel strong to locally severe Thunderstorms. Look for a dry start to July with a return of heat and thunderstorms by the 4th. && .NEAR TERM /THROUGH TONIGHT/... Today starts out on the chilly side (north) to comfortable in the south with temperatures ranging from the mid to upper 40s across the Northern Mtns to between 55 and 60 in the southern valleys. Some minimal valley fog was noted throughout the deeper river valleys of northern PA. Variable amounts of cirrus and cirrostratus will stream southeast across the region this morning, followed by some periods of opaque alto cu clouds during the midday and afternoon hours as mid level warm advection increases after a ridge of high pressure slides off to the east. Highs temperatures today will range from 75-85F. && .SHORT TERM /SATURDAY 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 /08Z FRIDAY THROUGH TUESDAY/... VFR conds will prevail through Friday with primarily high cirrus and fair weather cu expected. The exception will be patchy fog in the northern Alleghenies. Restrictions are possible at BFD between 07z and 13z, but confidence is less than 25 percent. Winds will be light and variable through sunrise, 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. The low stratus is expected to lift and become broken to scattered before showers and thunderstorms develop later on Saturday. The chance for showers and storms will linger into Sunday as a cold front swings through the area. Outlook... 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...Lambert NEAR TERM...Lambert SHORT TERM...Lambert/Steinbugl LONG TERM...Jurewicz/Steinbugl AVIATION...Martin/Colbert CLIMATE...Steinbugl