Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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950 FXUS61 KCTP 211901 AFDCTP Area Forecast Discussion National Weather Service State College PA 301 PM EDT Sat Sep 21 2024 .SYNOPSIS... A frontal system will fall apart as it moves through Central PA over the next 12 hours. Mostly cloudy, but rain-free weather returns for Sunday, before a slow-moving trough brings the next chance of rain from Monday through midweek. && .NEAR TERM /UNTIL 10 PM THIS EVENING/... All still holds from earlier disco with storms right on time, and dying right on cue as they enter the western zones. The lower CAPE/DCAPE numbers are doing their bit to diminish the intensity of these storms. SPC Meso Analysis forecasts (RAP) show the llvls/atmos over the central mtns continuing to look highly unfavorable for more then 1 or 2 really ambitious storms to get severe. Recent MCD from SPC points out that there are still some params that point to positive/increases in potential for severe winds. But, overall the threat looks very weak. Prev... Temps heating up away from the stratus deck in the east. Surface winds out of the east will keep it more-stable in the east this afternoon and evening. The SPC MRGL risk for today remains as is, with the central and western zones still under a risk of severe, but mainly near-severe storms. However, a lightning risk is there for most of the area, so factor this into any outdoor activities you may have planned for the aftn/eve. The front i more an occlusion already and still back over OH. As the upper flow nudges it this way, storms will continue to fire up, but coverage should be sct for much of the time in the axis of best instability. As we get into the evening hours and early night, the upper low/storm off the coast will exert more influence and stall out the showers/storms, and the increasing stability from earlier rain and loss of daylight/heating should take away the thunder risk. Showers may linger (per most guidance) well into the night over the eastern half of the CWA. The near-severe threat also decreases in the evening, perhaps very early in the evening. && .SHORT TERM /10 PM THIS EVENING THROUGH SUNDAY NIGHT/... Forcing pushes east of the area tonight, but lingering showers and storms may occur into the middle of the night. After that, little instability (even aloft) is seen in the CAMs. So, only light showers are expected to linger in the south central and south east. A cold air damming scenario renews as the flow in the east remains from the east. Typical CAD mass features make this pretty clear. Prev... Forecast soundings indicate an upsloping southeast flow will result in persistent stratus and perhaps a bit of fog or drizzle over the central/east zones for Sun and Sun night. The cloud cover and flow off of the Atlantic should result in markedly cooler afternoon temps Sunday than on Saturday, with highs likely stuck in the 60s over the Central Mtns. Sun night looks mainly dry with prev anticipated forcing holding off a bit longer/later. && .LONG TERM /MONDAY THROUGH SATURDAY/... Surging PWATs with enhanced energy from an upper-level trough will bring about an unsettled pattern throughout much of the long-term period. Deterministic model guidance is in fairly good agreement that a low-pressure stationed over the southern Great Lakes will bring about shower activity on Monday; however, model guidance has trended slower with the onset of rainfall and have chopped PoPs throughout the early period of the day as models tend to converge on a (slightly) slower progression. The best chances of showers will come across the Laurel Highlands during the late morning hours, continuing eastward throughout the afternoon/evening hours. Elevated instability will be highest across the western third of the area, so have limited mentions of storms to this area during the PM hours. 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 system coupled with enhanced moisture, have retained likely PoPs in the Tuesday to Wednesday timeframe. Given PWATs in the 1.50-1.75" range on Wednesday, locally heavy rainfall will be possible and this has been outlined with marginal (level 1/4) risks in the D4 (W) and D5 (E) Excessive Rainfall Outlooks from the Weather Prediction Center. Impacts at this time look less likely at this time given ongoing dry conditions across especially SW PA where D2 drought conditions persist; however, any heavier rainfall in the preceding days could allow for slightly more impacts. As we shift into the later part of the week, slightly more model uncertainty with regards to low-pressure moving N/E of the area and how this will impact rainfall chances for Central PA. At this time, have capped PoPs at a chance for Thursday as the low-pressure system will be slightly closer to our eastern half, and capped at a slight chance for Friday, keeping close to NBM model guidance in this timeframe. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... MVFR ceilings have persisted across the eastern airspace this afternoon with the cloud deck showing no clear signs of eroding over the next couple of hours. Some (minimal) improvement is progged by model guidance in the 20Z-00Z Sunday timeframe thus have outlined a brief period of improved conditions at IPT, MDT, and LNS with low-end VFR ceilings. Deterioration will quickly come across west-to-east this afternoon into the early evening with SHRA/TSRA. MVFR ceilings will generally be observed, although if TSRA manages to make a direct pass over the airfield could realistically see IFR to LIFR conditions. At this time, low confidence in this occurring predates mentions in the TAF package as current radar trends show the bulk of TSRA activity moving N/S of JST/AOO. Further east, less likely to experience IFR/LIFR restrictions as TSRA weakens as it approaches stable air near UNV and further eastward. Overnight, higher confidence in IFR/LIFR across central Pennsylvania although there is slightly lower confidence at BFD as the bulk of shower activity has stayed clear of the airfield and the ground has more time to dry out this evening. GLAMP model guidance and HREF probabilities continue to suggest fog formation, so have trended towards GLAMP guidance this cycle. As sunrise approaches, very slow improvement is expected with the bulk of airfields expected to stay sub-VFR through 18Z Sunday with exceptions at BFD/JST. Outlook... Mon-Thu...Scattered showers, restrictions possible. && .CLIMATE... The high temperature in Bradford on Friday set a new record high of 82 degrees. This broke the record of 81 degrees set in 1978 and 2016. The first day of autumn 2024 (Fall Equinox) begins at 8:44 am EDT on Sunday September 22nd. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...NPB AVIATION...NPB CLIMATE...Steinbugl/Martin/NPB