FXUS61 KCTP 031022 AFDCTP Area Forecast Discussion National Weather Service State College PA 622 AM EDT Sat May 3 2025 .SYNOPSIS... * Several rounds of showers and scattered afternoon and evening thunderstorms for today with the strongest storms and likely heaviest rainfall of locally over one inch occurring near and to the south of Interstate 81. * A few storms this afternoon and evening may produce damaging wind gusts and large hail over the Lower Susquehanna Valley. * Largely beneficial multi-day rainfall event shaping up for Sunday through Tuesday; some minor flooding will be possible with any repeated rounds of heavy rain && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The most contours on the latest sfc map intersect over Central PA and the Susquehanna Valley, and that's not a good thing IF you're not a fan of active convective weather and/or locally heavy rainfall. A quasi-stnry frontal boundary extends from a weak sfc low (1010 MB) near KCAK early this monring ESE along the I-80, and then along the length of the RT 322 corridor from KFIG to KUNV and KMDT. A lee trough extends south from this boundary to KMRB and near the I-81 corridor through VA. Several KFT AGL (in the 925-850 mb layer), we see two distinct frontal boundaries - one centered just NW of the I-81 corridor and the second from NW Ohio to KIAG and KBUF. The primary upper level jet axis extended from the Lower Glakes to the Lower St Lawrence Valley. Combining the aforementioned features we arrive at a broad area of light to moderate rain over the Laurel Highlands and NW Mtns, while a few additional showers were forming along and just north of the sfc stationary front across the Lower and Mid Susq Valley. Plenty of cloud cover in multiple layers will be found across the entire region today, which will put in question the instability ingredient of a good convective recipe for today. Latest HREF does create pockets of MU CAPE exceeding 1000 J/KG in a moderately sheared low-mid level environment over the Lower and Susq Valley later this afternoon into this evening, with numerous cells developing max 1 hour 2-5 KM helicity values over 75 m2/s2 near and to the SE of the I-81 corridor. SPC has addressed these aspects of today's convective event with the SLGT for Svr TSRA across roughly the SE third of the CWA. 24 hour max 2-5 KM updraft helicity is forecast to be centered over the KMDT/KMUI and KLNS area. LCL heights per NBM guidance will rise to 3500-4000 ft at the time of peak heating today, but will gradually lower to 1500-2000 ft after 22Z, which will pose the best chance for seeing an isolated weak tornado from any of the stronger TSRAs , especially those that drift over the quasi-stnry boundary forecast to linger near the I-81 corridor from the greater Harrisburg area, northeast. For the rest of the forecast area, look for several rounds of light to moderate, beneficial rain showers today, and a few brief periods of heavy rain from embedded, fairly low topped TSRA. Basin average mean QPF today will be on the order of 0.5 to 1.0 inch, though any location receiving 2-3 TSRA could easily see upwards of around 2 inches. WPC has all but the Northern Tier counties in their MRGL risk for excessive rain today and tonight. Highs today will highlight the quasi stnry boundary with locations across the Lower Susq Valley topping out in the 80-83F range, while the northern tier counties will struggle to make it above 60F. && .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/... Blocking pattern sets up over the fcst area through this weekend with a deep/vertically stacked low in the OH Valley. The upper level closed low meanders in the Ohio Valley into early next week. Southerly flow on the east side of the low will channel moisture into the area with periods of rain expected Sunday and Monday. While rainfall will be certainly beneficial and bring some relief to drought conditions particularly in the southeast part of the forecast area, we will need to monitor conditions for repeated rounds of heavy rainfall which could produce locally heavy totals and may result in localized flooding in urban and poor drainage areas. WPC has maintained marginal excessive rain risks for Saturday-Monday. This period will remain mild relative vs. climo with the largest departures from normal in the overnight min temps on the order of +10-20F above the historical average. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Blocky pattern with closed low lifting very slowly to the northeast from the Ohio Valley will maintain a strong wet pattern signal over the area through midweek. Initially, rainfall should be beneficial particularly over the southeast zones/Lower Susq where D1/D2 drought conditions have persisted for some time. WPC has indicated a marginal risk of excessive rain with some potential for repeated rounds of rain capable of producing localized flooding risk in urban and poor drainage areas. The main uncertainty in the forecast period is in regard to how quickly the upper low begins to move off to the east. Some guidance suggests a mainly dry second half of the week as high pressure builds in behind the departing upper low, while some models keep the low around a little longer. Because of this uncertainty, we have not deviated from the NBM through the end of the extended period. && .AVIATION /10Z SATURDAY THROUGH WEDNESDAY/... As of 615 AM skies mainly clear to the southeast of the office here, with some showers to the west. Adjusted TAFS for this trend, TAFS will be sent by 730 AM. Patchy fog did form earlier, but is mainly gone as of sunrise. Otherwise not a lot dhange for the 12Z TAFS. Earlier discussion below. Looking at clear skies with some fog across the region early on, then the remains of showers and storms to the west will taper the fog at sites like UNV and AOO, as there will be more clouds in a few hours. For most of the day, expect some showers and storms to form again, with a wide range of conditions. No real change to the pattern before the middle of next week. There will be a daily chance of showers and storms over the next few days. Outlook... Sun-Tue...Frequent rain showers; some locally heavy with prolonged sub-VFR conditions. Wed...Some improvement expected with a decreasing chance of showers. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert/Steinbugl/Bauco NEAR TERM...Lambert/Bauco SHORT TERM...Lambert/Steinbugl/Bauco LONG TERM...Steinbugl/Bauco AVIATION...Martin