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Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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293 FXUS61 KCTP 200017 AFDCTP Area Forecast Discussion National Weather Service State College PA 817 PM EDT Fri Jul 19 2024 .SYNOPSIS... * High pressure over the region will maintain dry weather and lower humidity into early Saturday. * Southerly winds usher in an uptick in humidity on Saturday with scattered afternoon showers and thunderstorms. * Dry conditions on Sunday into Monday precede a more unsettled pattern next week with seasonable temperatures. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... A ridge of high pressure extending from Indiana into PA was linked to/supported by broad subsidence beneath the thermally direct left entrance region of a 60-70 kt zonal jet core extending from the Ohio River Valley to the Southern New England Coast. PWATS averaged around 7 tenths of an inch across the CWA this afternoon - a refreshing chance from the extended heat and humidity earlier this week. The sharp gradient in PWAT seen across Central and Southern VA at 18Z today - with the main gradient of Theta-E air in the 850-700 mb layer seen further north about 50 NM either side of the Mason/Dixon line, will both lift north as the two favorable quadrants for ascent in association with second, slightly anticyclonically curved upper jetlet lift north across PA late tonight into Saturday, with the jet strengthening slightly. Patchy fog could again develop again tonight into Saturday morning across the NW mtns given the increasing moisture and scattered cloud cover expected, though coverage is not expected to be as extensive as this morning. Morning lows on Saturday will trend a few degrees warmer than this morning - from the middle 50s in the northwest to upper 60s southeast. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... As the aforementioned sfc high slides east and off the Mid Atlantic Coast developing SE-southerly sfc flow and south- southwesterly flow through about 7-8 KFT AGL will advect increasing clouds north into the state very late tonight/early Sat. Trimmed POPS to under 10 percent through the early morning hours Sat, and made just slight upward adjustments to cloud cover while maintaining the overall SCHC to CHC pops for SHRA/SCTD PM TSRA as PWATs increase to between 1-1.5 inches from NW PA to SE PA respectively. There appears to be a fairly significant, 7-8 kft thick layer of dry air between the low clouds and a thickening layer of cirrus/high altostratus, which should prevent much opportunity for significant drop formation/ QPF amounts. Min temps tonight will be about 6-8 deg F warmer that last night as moisture and clouds gradually increase from the south late. Lows will be in the mid to upper 50s across the north and mainly mid to upper the southern valleys. Pertinent/still valid points of the previous disc... A short wave disturbance will bring increased rain chances for the afternoon on Saturday when isolated to scattered coverage of showers and storms develops over parts of the Laurels, SC Mountains and Central Mountains. Best chance for rain appears to be along the spine of the Appalachians with current rainfall amounts generally less than a tenth of an inch, with isolated pockets exceeding 0.5 inches possible. Generally weak forcing, shear and instability will almost certainly preclude any severe TSRA or flooding potential as the SREF probability of CAPE exceeding 1000 J/KG is 20 percent or less from KELM to KBFD and SW to KJST and KPIT. In fact, with expanding drought conditions across the region, rainfall will be beneficial for all recipients. There will be a noticeable uptick in humidity on Saturday from the 24 hours prior for everywhere except the northwest mountains with temperatures staying pretty steady relative to Friday. If anything, we could be several degrees too bullish on temps based on the increasing cloud cover after the largely clear to partly cloudy first half of tonight with decent radiational cooling. High pressure will regain control of our weather Saturday night with clearing skies expected and patchy fog in locations that received rain earlier in the day. Dry conditions prevail on Sunday with increasing clouds but still partly cloudy skies. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Temperatures will trend a few degrees above normal Sunday afternoon as high temps across the south approach 90 once again. Dry weather continues Sunday night as clouds continue to stream in and humidity increases. The uptick and clouds and humidity will help overnight lows continue to moderate each day into next week. Near to below normal pwats beneath a weak area of high pressure will provide a rain-free and less humid end to second-to-last weekend of July. There should also be good viewing at night for the full Thunder or Buck moon with patchy fog developing in the northern river/stream valleys into early Monday morning. Latest model and ensemble guidance shows an amplified pattern that will be fairly slow to evolve next week. The key synoptic features will be a wavy front on the leading edge of a Great Lakes to southern Plains mean trough that will promote multiple days of diurnally enhanced thunderstorms and potential heavy rainfall across the region. The southern tier of central PA could really use some rain to lessen the impacts of moderate to severe drought conditions (D1-D2 drought monitor). Max/min temperatures (80-90/60-70F) will remain above the historical average with for late July with humidity/dewpoints returning to elevated levels; however the heat and humidity combination is not expected to be excessive. WPC introduced a marginal risk ERO for day 5/Tuesday with guidance ramping pwats to 1.5-2.0 inches or +1-2SD. The Tuesday into Wednesday timeframe appears to have the best odds for heavy rainfall (max POPs) before pwats trend lower from NW to SE as the frontal zone slowly presses to the southeast with time by late week. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... High cirrus will be on the increase overnight as an upper level disturbance moves north out of the southern Appalachians. Most airfields will remain VFR through the night, although patchy valley fog is expected once again in the northern valleys. Opted not to include vsby restrictions at BFD in the 00z TAF package and instead went with VCFG, but the LAMP does still show nearly a 50 percent chance of IFR or lower vsby at BFD late tonight into early Sat morning. Midlevel clouds will thicken after 12z Sat, with scattered rain showers and potentially a few areas of stratiform light rain developing. A few thunderstorms are possible as well, but low CAPE will be a limiting factor. Most airfields will remain VFR through the TAF period. Outlook... Sun...Primarily VFR. Patchy late night/early morning fog and low ceilings are possible. Mon...Primarily VFR. Patchy early morning fog possible. Scattered afternoon SHRA/TSRA. Tue...More widespread PM SHRA/TSRA could lead to at least brief restrictions. && .CLIMATE... The average temperature from July 1 to July 18 at Harrisburg is 81.6F which is the warmest July month-to-date. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert/Banghoff NEAR TERM...Lambert/Banghoff SHORT TERM...Lambert/Banghoff LONG TERM...Steinbugl AVIATION...Colbert CLIMATE...Steinbugl