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Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --653 FXUS61 KCTP 230443 AFDCTP Area Forecast Discussion National Weather Service State College PA 1243 AM EDT Mon Sep 23 2024 .SYNOPSIS... Welcome to Autumn! An amplifying upper level trough and slow moving frontal boundary headed our way from the midwestern states will bring several periods of rainy conditions across Central Pennsylvania beginning Monday morning and lasting through at least Wednesday. && .NEAR TERM /THROUGH TODAY/...-- Changed Discussion --A veil of mid and high clouds has increased over central and eastern portions of central PA early this morning. Lower cigs are found over the NW/WC Mountains and Laurel Highlands and now spilling eastward into the NC and C mountains, with light rainfall moving into the NW Mountains. Regional radar mosaic and gage reports indicate most of the initial reflectivity returns are aloft and only T amounts reported south of Erie in the past 1-2 hours. Clouds will continue to increase, thicken and lower overnight. Temps should again stay much warmer than normal tonight, with most places at least 10F above normal. The approaching sfc frontal system runs into the CAD in place over Central PA and stalls, so eastward progression of whatever precip does make it into the Alleghenies overnight will be a chore. Still, moisture transport aloft is continuous overnight and rain/showers will eventually spread across much of the western half of our CWA through sunrise. The plume of moisture overhead continues eastward and hangs over the CWA most of the day on Monday. Heavy rain signal is not there, but there might be a thunderstorm or two, more probable in the SW than E. Temps on Monday won`t go more than 10F above the morning numbers. Some places may not get much more than a 5F deg diurnal swing. Highs Monday will be mainly in the low to mid 60s in most places, except for around 70F across the Lower Susq Valley.-- End Changed Discussion --&& .SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/... The 5H ridge axis doesn`t go east of our longitude, so the showers might not get to the far eastern reaches of the CWA early Mon night before fizzling. Another minor surge of WAA and moisture aloft arrives in the Laurels before sunrise Tuesday. So, the chcs for rain increase once again. PWATs get around 1.5" Mon aftn before dipping then rising again later at night. The storm motion doesn`t seem slow enough to make a widespread risk of flooding. Basin average QPF total is only 0.5-0.75" at highest. But, any storms can drop that much in a short time with PWATs in that range. Still, a big factor against any flooding is the very dry antecedent conditions, esp in the Laurels. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...-- Changed Discussion --Model guidance outlines another surface low-pressure system tracking northeastward across western portions of the Upper Ohio Valley and into southern Ontario Tuesday into Wednesday, with slightly more moisture and lift available as the warm front aligns itself north-to-south across west-central PA. Given slightly better lift with this low-pressure systemoverhead co coupled with enhanced moisture, have retained likely PoPs in the Tuesday to Wednesday timeframe. Given PWATs in the 1.25-1.75" range on Wednesday, locally heavy rainfall will be possible with relatively slower storm motion also possible. This threat has been outlined with marginal (level 1/4) risks in the D3 (area wide) and D4 (SE 1/2) Excessive Rainfall Outlooks from the Weather Prediction Center. Highest impacts are expected to be across areas that have recently received heavy rainfall, such as urban areas of the Lower Susquehanna Valley, along with hydro sensitive areas across the northern tier. Model uncertainty in previous packages still remain late Wednesday/early Thursday and into the end of the long-term period, so there is low confidence as we move past Thursday morning on this forecast cycle. A (potentially) slower progression of the departing low- pressure system retains chances through Thursday, with slightly lower chances as we move into Friday. The remnants of a tropical cyclone could also bring about rain chances this weekend, but uncertainty with respect to interactions with a trough that could limit chances of precipitation/increase chances as we get closer to an event. At this time range, have maintained numbers close to NBM guidance which continues to paints SChc PoPs (~15-25%) or below across the western PA with some enhancement of precipitation along the Laurels.-- End Changed Discussion --&& .AVIATION /06Z MONDAY THROUGH FRIDAY/... High clouds are beginning to stream in from the west as an upper trough pushes off the great lakes. This coupled with a building low stratus deck will signal the lowering of cigs generally throughout the evening. Lower ceilings will gradually make way into the western terminals at the beginning of this TAF package with GLAMP model guidance suggesting JST/AOO/UNV will be the first terminals to trend towards MVFR restrictions based on ceilings. There remains some signal for low-level clouds to begin making way into IPT/BFD slightly earlier; however, lower confidence on this solution so have outlined scattered low-level clouds to outline this potential after 03Z Monday. Many sites will likely see IFR cigs before sunrise. Closer to sunrise, SHRA is expected to begin entering W PA and have outlined a general west-to-east onset of VCSH/SHRA from 08Z-11Z Monday. Relatively drier air at the lower-levels could slow down timing of SHRA at MDT/LNS so have progged these conditions closer to the 14-15Z Monday timeframe with slightly lower confidence. With SHRA onset, borderline MVFR/IFR ceilings start to become a concern with the HREF/GLAMP guidance suggesting all airfields outside of MDT/LNS experiencing periods of IFR thresholds. If IFR thresholds manage to get into the airfield, generally expect these conditions to hold through the end of the TAF period. Outlook... Tue-Wed...Chc/Likely SHRA with some TSRA possible. Thu...Lingering/scattered showers possible area wide. Fri...Scattered SHRA SW PA; otherwise, trending drier. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert/DeVoir/Dangelo NEAR TERM...Lambert/DeVoir/Dangelo SHORT TERM...Lambert/Dangelo LONG TERM...Lambert/NPB AVIATION...NPB/Bowen