Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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004 FXUS61 KCTP 281758 AFDCTP Area Forecast Discussion National Weather Service State College PA 158 PM EDT Fri Jun 28 2024 .SYNOPSIS... *Seasonably warm and pleasant today; increasing clouds tonight *Heat and humidity spike fuels severe T-storm risk this weekend *Refreshing/dry start to July; heat+T-storms return by the 4th && .NEAR TERM /THROUGH TONIGHT/... Mostly sunny to partly cloudy and pleasant wx conditions across central PA for the last Friday of June. Highs temperatures this afternoon will range from 75-85F which is quite seasonable for this time of year or within +/- 2 to 4 degrees of the historical average for late June. Increasing clouds expected tonight as warm air and moisture advection ramps up across the area. There is a strong signal for low clouds to develop/expand late tonight into early Saturday morning particularly east of the Allegheny spine. Still can`t rule out a couple of showers/elevated convection over the far NW mtns prior to 12Z; however hires guidance appears to be focusing in on a period of heavy rain in the following 6hr pd. && .SHORT TERM /SATURDAY THROUGH MONDAY/... Latest HREF now shows 40-50kt LLJ from the south southwest driving 2+ inch pwats into NW PA Saturday morning. The QPF response is noteworthy with both 3/6hr PMM indicating 1-2 inches during the period ending 18Z Sat. If this signal remains bullish with later hires ensembles, a short fused FF watch may be needed given reduced FFGs over the NW/N-central zones fostering increased vulnerability to short duration flooding. The early morning low clouds forecast across the central mtns into the Susquehanna Valley, along with the potential heavy rainfall evolving across NW PA Saturday morning both complicate the convective forecast for later Saturday afternoon and evening. There is a conditional element now in play which hinges on amount of instability/destablization that can be realized. That being said, very little change to the SPC SWO for tomorrow with the 1730Z update. 5% tornado risk remains largely unchanged and hail probs were removed. The belt of strong 850mb flow will transport rich low level moisture (dewpoints in the upper 60s to lower 70s) northeastward along/ahead of a cold front this weekend. PWAT values are forecast to reach 2-2.5 inches on Saturday or +2-3SD. The anomalous, deep-layer moisture will support risk of heavy to potentially excessive rainfall with point amounts of 3 inches possible in places experiencing multiple TSRA. WPC added a SLGT risk across NW PA overnight which looks good given increasing confidence in an initial round of +RA over that area prior to 18Z. They may even expand the SLGT risk area a bit with the next update later this afternoon/20Z. Storm motions and much higher FFGs (due to lack of rainfall) will be limiting factors to reduce flood risk farther to the south and east across the CWA (where D0 and D1 drought conditions exist). Convection/heavy downpours should be sustained after 00Z and probably not exit the area until after midnight/06Z Sunday. Guidance continues to show some variability with the timing of the main frontal passage on Sunday. Locations most likely to see potential strong/svr t-storms are over the southeastern part of the CWA which is included in the D3 SLGT risk SWO. Once the cold front clears, the door will be open for another seasonably cool/dry airmass to invade the Commonwealth. This will result in a less humid and comfortably dry start to July on Monday. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... On the large-scale, a fairly zonal upper-level flow pattern will stay in tact over the northern tier of states next week, with energetic short-waves traversing this flow every 3-4 days or so. Consequently, expansive summertime upper ridging will largely stay south of PA, keeping excessive heat mainly out of the forecast for the time being. Looking at the daily sensible weather, as one of the above mentioned short-waves presses through eastern Canada and New England early next week, it will push a surface cold front well to the southeast of the Commonwealth, bringing another stretch of dry conditions and comfortable temperatures/humidity levels for Monday and Tuesday. Confidence in this scenario is relatively high. By the middle of next week, as a surface high pushes offshore and heights aloft begin to build, summertime heat and humidity should at least temporarily make a run at PA. At the same time, though, the next upstream surface cold front and upper-level trough will be approaching from the northwest. The most likely scenario here is for increasingly muggy conditions and higher chances for showers and thunderstorms. Just how hot temperatures are able to get, or robust convection becomes, is fairly uncertain. Better knowledge of these factors will require considerably more time and additional model runs to see how atmospheric features resolve themselves during this time frame. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... VFR conds will prevail through Friday with primarily high cirrus and fair weather cu expected. The exception will be patchy valley fog in the northern Alleghenies early this morning. Winds will start the day light and variable, then veer to become S to SE later in the day on Friday with gusts generally less than 20 kts. As a warm front approaches late Fri night into Saturday, southeast flow will bring increasing moisture and the potential for low stratus across southern and eastern PA. Confidence is relatively high in restrictions after 06z Sat for airfields from UNV eastward, with a 25-50 percent chance of IFR conditions at MDT and LNS. Overnight rain and some thunder is possible especially in the north, mainly after 06z. Some marginal LLWS is also possible mainly in the north. The low stratus is expected to lift and become broken to scattered before more numerous showers and thunderstorms develop later on Saturday. The chance for showers and storms will linger across the southeast into Sunday as a cold front swings through the area. Outlook... Mon-Tue...Dry weather with VFR conditions. && .CLIMATE... Through 6/27, June ranks as the second warmest on record at Harrisburg with an average monthly temperature of 76 degrees or +3.8 degrees above normal. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Steinbugl NEAR TERM...Steinbugl SHORT TERM...Steinbugl LONG TERM...Jurewicz/Steinbugl AVIATION...Martin/Colbert CLIMATE...Steinbugl