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Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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188 FXUS61 KCTP 131758 AFDCTP Area Forecast Discussion National Weather Service State College PA 158 PM EDT Sat Jul 13 2024 .SYNOPSIS... *Another heat surge/significant heat wave is headed our way for Sunday- Wednesday with max heat index 100-110 over parts of south central PA and the Susquehanna Valley *While an isolated late afternoon or early evening thunderstorm can`t be ruled out, most places stay dry this weekend. There is some potential for more organized/severe thunderstorms Monday through Wednesday *Relief from the sweltering heat probable Thursday-Friday && .NEAR TERM /THROUGH TONIGHT/... Rising heights, dry mid levels, and weak sfc high pressure extending from the Lower Great Lakes into PA will bring a nice, warm early Summer day with abundant sunshine and dry weather over the vast majority of Central PA. However, passage of a weak surface trough, combined with strong diurnal heating, and lack of a significant cap in model soundings opens the possibility (10-20% chance) of an isolated thunderstorm later this afternoon through the evening hours. Additionally, subtle llvl convergence zones (across the Northern Tier counties and Laurel Highlands) leading to some building cu this afternoon, especially across the southeast- facing slopes of the Laurel Highlands where the better late morning/early afternoon heating occurred. Will linger SCHC POPS for several of our Scent/SW counties into the evening hours and diminish them elsewhere where terrain and any outflow boundary effects to enhance additional convection will be minimal. Early afternoon temps are right on track to reach highs ranging from the mid 80s acrs the Northern and Western Mtns to the Low 90s in many of the Southern Valleys and Susq region...or +5-10 degrees above mid July climo. Tonight will be mainly clear and muggy with areas of fog and min temps 60-75F or +5-10 degrees above the historical average. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... Another rather nice (but very warm to hot), rain-free summer day is on tap for most of the area Sunday, thanks to surface ridging and dry mid level air over Central PA. GEFS shows a channel of near normal (approx 1 to 1.2 inch PWAT air extending from the NCent Mtns to the Laurel Highlands on Sunday with values around 1.5 inches across the far West and SE parts of the state. Still, these PWAT values ahead of a weak shortwave combined with strong heating/instability should be able to produce isolated to widely scattered convection from the mid afternoon into the evening (15-25% chance). 850mb temps near 20C support highs in the upper 80s to mid 90s Sunday. While mixing of drier air aloft may result in a slight reduction in dewpoints during the afternoon, fcst max HX around 100F has prompted the issuance of a heat advisory for the Lower Susquehanna Valley. && .LONG TERM /MONDAY THROUGH SATURDAY/... No significant changes from the previous guidance runs. Confidence is increasing for the likelihood of thunderstorms crossing the state on Wednesday as the cold front pushes through. Mainly fair weather is currently expected for the beginning of the weekend. Prev... Heat pattern ramps up and peaks early next week as a large Bermuda high pumps increasingly hot and very humid air into CPA. 850mb temps rising to around 22C supports highs peaking between 90-100F with max heat indices 100-110F. High confidence in excessive heat risk lead to the issuance of a heat advisory for the south central Alleghenies and middle Susquehanna Valley Mon & Tue and xheat watch for the lower Susq where max heat index could reach 105-110F. The interaction of modest shortwave trough with very warm and humid airmass should trigger PM t-storms on Monday. Shear will likely be weak, mitigating the organized storm potential and keeping the severe threat isolated/limited. Another round of at least semi-organized/possible severe convection is possible Tuesday PM ahead of cold front pressing southeast through the Great Lakes toward Lake Erie. The latest GEFS and EPS both track a cold front into the region Wed PM, likely accompanied by a round of showers/tsra, some of which could be severe. Heat index values will likely push 100F or advy criteria over the Lower Susq Valley Wednesday afternoon. High pressure building in from the Grt Lks will likely bring a return to fair and seasonable weather late next week (Thu-Fri), with much lower humidity. However, there is some model spread regarding how far south the dying cold front gets, so can`t completely rule out convection lingering over the Southern tier counties, especially on Thursday. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... Predominantly VFR conds will be found across central PA through the rest of this afternoon/evening. Highly isolated showers or thunderstorms will pop through 00Z Sunday, but coverage will be sparse and practically all locations should stay dry. Winds will be light and variable in direction today (generally 5 kts or less). After any convective wanes this evening, clear skies and light winds will allow patchy fog to develop once again tonight. Outlook... Sun...AM fog quickly dissipating. A late-day SHRA/TSRA is possible. Otherwise, predominantly VFR. Mon-Wed...Scattered SHRA/TSRA possible areawide Monday and Tuesday with the best chance coming Wednesday afternoon/evening with the passage of a cold front. && .CLIMATE... The duration of warm nights is noteworthy -- Harrisburg has not dropped below 70 degrees since July 3rd. Here are the longest stretches with temperatures at or above 70 on record at Harrisburg. # OF DAYS DATES YEAR 17 7/19-8/04 2020 13 8/16-8/28 2021 13 7/13-7/25 2010 12 7/18-7/29 2022 12 7/17-7/28 1999 12 7/20-7/31 1940 11 8/04-8/14 1977 10 8/10-8/19 2016 10 7/14-7/23 2013 10 8/01-8/10 1968 10 7/21-7/30 1898 9 12 times, most recently 7/3-7/11/2020 8 7/04-7/12 2024 ................................................. The minimum temp dipped to 68F yesterday morning (7/12) and therefore ends the streak at 8 consecutive days. Tonight will start another run of lows >=70F which should last until next Thursday night (7/18 or morning of 7/19). && .CTP WATCHES/WARNINGS/ADVISORIES... Heat Advisory from noon Monday to 8 PM EDT Tuesday for PAZ019- 025>028-034-035-045-046-049>053-058. Heat Advisory from noon Sunday to noon EDT Monday for PAZ036- 056-057-059-063>066. Excessive Heat Watch from Monday afternoon through Tuesday evening for PAZ036-056-057-059-063>066. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert/Steinbugl LONG TERM...Fitzgerald/Bowen AVIATION...Lambert/Evanego CLIMATE...Steinbugl/Banghoff