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Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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874 FXUS61 KCTP 150851 AFDCTP Area Forecast Discussion National Weather Service State College PA 451 AM EDT Mon Jul 15 2024 .SYNOPSIS... High pressure will remain near Bermuda for the first part of this week, resulting in a prolonged heat wave over the region. A compact but potent upper level disturbance and strong winds aloft will bring a round of strong to severe thunderstorms that will be focused across Central PA and the Mid Susquehanna Valley later this afternoon and evening. A cold front will push southeast across Pennsylvania late Wednesday with another round of strong to severe thunderstorms, then high pressure will build in from the Great Lakes late in the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Fairly tranquil, but warm and humid conditions with variable amounts of clouds and even a few showers were present across central and northern PA early this morning. A relatively flat mid/upper level shortwave and associated weak sfc streamline convergence with mostly cloudy to overcast skies were noted on regional sat loop and mesoanalysis approx 40 NM either side of a line from KCBE to KUNV and KELM. This feature aloft could spark a few showers or a TSRA across the Susq Valley around and shortly after daybreak today, where the latest RAP and 03Z SREF display higher instability, SREF indicates 40-70 percent chcs for CAPE to exceed 1000 J/KG through 13-14Z near and to the east of the Lower and Mid Susq Mainstem. Virtually no chc of exceeding 1000 j/KG across the Central and Western Mtns during this time, considering that a slight PWAT min of around 1.3 to 1.4 inches was found across the western half of the CWA with PWATs of 1.6 inches across far Western PA and Sern PA. Min temps at sunrise today will range from the mid 60s in the coolest northern valleys to the mid 70s in the more urbanized spots of the Lower Susq Valley. Diurnal heating, combined with the approach of a more potent shortwave/MCV (extending from Southern Lower Mich into Indiana and NW Ohio at 0830Z) will be accompanied by a belt of strong 40 to 50 kt WSW to SWrly winds later this morning and this afternoon. This prompted SPC to coordinate a SLGT risk SVR area for this afternoon and this evening that extended from Central and Western NY south into the Middle Susq Valley and Ncent PA. The severe weather threat will be focused on strong to potentially damaging straight line winds from mid level jet inflow/mini bow echoes embedded within a bkn line of TSRA, not to mention the possibility of even a few discrete supercells given broad looping hodographs with helicity values of 250-300 m2/s2 and mean storm motion from 280-290 deg. The more-certain wx problem will be the heat. An excessive Heat Warning covers the Lower Susq Region for this afternoon and Tuesday afternoon with little relief during the overnight hours tonight. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... After the convection diminishes and/or moves east and out of the area, weak ridging at the sfc and aloft builds across the Commonwealth tonight. Mins again will range from mid 60s in the northern valleys to the mid 70s in the urbanized areas of the Lower Susq Valley. Heat wave peaks Tuesday afternoon, 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 100-105F southeast of the Alleghenies. High confidence in excessive heat risk lead to the issuance of a heat advisory for the south central mountains and Middle Susquehanna Valley Mon & Tue and an excessive heat warning for the Lower Susq Valley, where max heat index around 105F appear likely. A 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. However, a better chance of more widespread showers/tsra is in the cards for Wed PM with the passage of the front. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... All medium range guidance supports a return to fair and seasonable weather with much lower humidity late in the week, as high pressure builds southeast from the Grt Lks. Will maintain just a slight chance of convection along the southern tier Thursday to account for some uncertainty regarding how far the dying cold front makes it south of the Mason Dixon Line. The stalled front is likely to return northward next weekend, resulting in the return of diurnal convection, mainly over the southern counties. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... At 06z, primarily VFR conds were found across central PA beneath patches of mid-level cloudiness. BFD has a 50-60% chc of seeing MVFR ceilings by daybreak, while the other TAF sites are expected to remain VFR. There is enough cloud cover and a bit of a breeze that fog is not expected for most locations. Monday will bring an increasing chc of showers/storms as the day progresses. The highest probability of seeing thunder will be across northern PA, so maintained VCTS for BFD, IPT and UNV this aftn/eve. Expect more of the same for Tuesday, before a potent cold front crosses the area in the midweek and ushers in a cooler and drier airmass for late week. Outlook... Tue...Scattered, mainly aftn, SHRA/TSRA possible. Wed...Numerous SHRA/TSRA, with some restrictions expected. Thu...Lingering -SHRA diminishing. Fri...No sig wx. && .CLIMATE... The duration of warm nights is noteworthy. Here are the longest stretches with temperatures at or above 70F 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 ................................................. && .CTP WATCHES/WARNINGS/ADVISORIES... Heat Advisory from noon today to 8 PM EDT Tuesday for PAZ019- 025>028-034-035-045-046-049>053-058. Heat Advisory until noon EDT today for PAZ036-056-057-059- 063>066. Excessive Heat Warning from noon today to 8 PM EDT Tuesday for PAZ036-056-057-059-063>066. && $$ SYNOPSIS...Lambert/Fitzgerald NEAR TERM...Lambert/Fitzgerald SHORT TERM...Lambert/Fitzgerald/Dangelo LONG TERM...Fitzgerald/Bowen AVIATION...Guseman/Evanego CLIMATE...Evans