Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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023 FXUS61 KCTP 050536 AFDCTP Area Forecast Discussion National Weather Service State College PA 136 AM EDT Fri Jul 5 2024 .SYNOPSIS... Warm and humid conditions will prevail through Saturday with daily chances for showers and thunderstorms. A few storms could produce strong winds and heavy rainfall on Friday. Low pressure tracking north of Pennsylvania will drag a cold front east of the state on Saturday, ushering in drier and more comfortable conditions for Sunday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... A few clusters of showers and isolated thunderstorms across south central PA and far northwest PA late this evening. Outflow boundary just south of the office late this afternoon is helping keep activity just to the south of State College for a nice view of local firework show. The activity has been weakening, and expect this trend to continue. Very high dewpoints will limit temperature drop overnight. Current low temps look to be on track. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... Mid evening update. Did cut POPS down for the morning hours, hard to see much going on at this time of day, with warm mid levels. Also did edge high temperature up a small amount, given the airmass in place, and that I cut down the chc of showers and storms in the morning hours. Earlier discussion below. Leftover outflow boundaries, increasing/swrly deep layer shear and healthy CAPE in the afternoon will set the stage for more Showers/TSRA later in the day. Previous... The stalled front over Central PA is progged to return north as a warm front Friday PM ahead of low pressure lifting across the Great Lakes. Falling heights and surging pwats ahead of an upstream shortwave and associated surface low lifting across the Great Lakes should bring a round of showers/tsra in the latest Friday PM to Saturday AM timeframe. Model shear/instability profiles indicate strong to severe tsra can`t be ruled out Fri PM. SPC expanded the previous DY2 MRGL risk area for SVR to cover all but the far eastern parts of our CWA. Current guidance suggests the mid level shortwave and bulk of the large scale forcing will pass north of PA, leading to unimpressive mean qpf in the ensemble plumes of 0.25 to 0.50 inches Fri PM to Saturday. However, locally heavier amounts will accompany stronger convection. The Weather Prediction Center has placed all of Pennsylvania in a Marginal Risk of Excessive Rainfall for 8am Friday through 8am Saturday to account for the multiple rounds of showers and potential for rainfall amounts approaching 2 inches in a few spots. Flash flood guidance across most of the region remains quite high (3" or more in 3 hours), so most of this rainfall should be beneficial. It is also worth noting that heat index values will approach or briefly touch 100F on Friday afternoon in southeast PA. Dewpoints in the low to mid 70s combined with high temperatures approaching 90 will result in a very hot and humid afternoon. With scattered convection in the forecast, there is not yet enough confidence to warrant a heat advisory but one may need to be considered if temps/dewpoints trend higher. Overnight lows into Saturday will also be quite mild, ranging from the upper 60s in northwest PA to the middle 70s in the Lower Susquehanna Valley. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Models show some variation from day to day, but main hint is that the eastern part of country is in a weakness at 500 mb. While we may still be warmer than normal, there will be a tendency to see at least some showers and storms from time to time. As noted below, after Friday, a decrease in dewpoints will result in a lower chance of showers and storms for the weekend. Main chance for showers and storms will be in the Tuesday to Wednesday time frame. Earlier discussion below. The aforementioned cold front is expected to mostly clear the region by Saturday morning, but some lingering showers across eastern Pennsylvania cannot be ruled out. Thunderstorms are slightly less likely at this time given increased cloud cover and lower instability of the early morning hours, but cannot rule out a thunderstorm across far southeastern Pennsylvania with some elevated instability. After the cold frontal passage, cooler and less humid air will rush in by Sunday morning. All medium range guidance supports fair weather and above average temperatures Sunday into early next week with upper level ridging indicated over the northeast. At the surface, high pressure is progged to build over Pennsylvania Sunday, then pass off of the east coast early next week. The return southerly flow should result in an uptick in heat/humidity early next week. Diurnally driven showers and thunderstorms appear possible on Monday based on recent GEFS plumes but guidance continues to suggest a better chance of precipitation on Tuesday with the arrival of a cold front during the afternoon hours. There is still a fair amount of uncertainty with regards to the cold front clearing eastern Pennsylvania later on Wednesday, so have retained PoPs through this timeframe. Towards the end of the period, deterministic guidance begins to outline high pressure influence into the region; however, given so much uncertainty earlier in the forecast period have opted not to deviate from NBM PoPs at this time. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... An area of showers is moving in from the west ahead of an MCV located over western PA. These showers will likely impact the visibility in the NW mountains during the overnight hours before they eventually push out of the region by sunrise. Fog and low ceilings will likely develop across almost all of Central PA overnight. The highest probabilities for IFR visibilities are at BFD and IPT, and the highest probabilities for IFR ceilings are at BFD, IPT, and JST. All other sites will likely see MVFR conditions tonight with brief periods of IFR possible. Conditions will improve to VFR fairly quickly after sunrise across most of the area, though it could take until late morning for BFD and IPT to see the low ceilings improve. Scattered showers and thunderstorms will be possible again later this afternoon, though coverage looks to be more limited than what occurred Thursday. Outlook... Fri...Sct TSRA w/ possible impacts; Mainly PM w/ highest coverage across the west. Sat...Sct to Nmrs TSRA areawide, highest chances SE in PM. Sun...AM fog possible; otherwise, no sig wx. Mon...SHRA possible SE late PM; otherwise, no sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert/Banghoff/Martin NEAR TERM...Martin SHORT TERM...Lambert/Banghoff/Martin LONG TERM...Fitzgerald/Martin/NPB AVIATION...Bauco/Bowen