Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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009 FXUS61 KCTP 261458 AFDCTP Area Forecast Discussion National Weather Service State College PA 1058 AM EDT Thu Sep 26 2024 .SYNOPSIS... *Mostly cloudy with periods of rain and mild nights through the early to middle part of next week *The heaviest rain over the next 5-7 days is expected over parts of south central PA which should provide relief in abnormally dry to moderate/severe drought conditions *A shift toward drier weather is possible by the end of next week/first weekend of October && .NEAR TERM /THROUGH TONIGHT/... 1045AM/1445UTC: Mid morning update coincided with radar trends and ramped POPs along fgen precip frontal zone extending from just north of Pittsburgh through State College to near KAVP/Scranton-WB. Otherwise, not much change for the last Thursday of September with cloudy skies and noticeable uptick in humidity. Previous Discussion Issued: 628 AM EDT Thu Sep 26 2024 Temperatures have trended up overnight, deviating from a typical diurnal pattern. It is amazing the difference a southerly wind can make after what has felt like an unending stretch of easterly flow. Quite mild at daybreak with temperatures in the 60s, which is +15 to +20 compared to average for this time of year. Heaviest rain showers are southeast of I-81 this morning, downstream of a corridor of 2-4" extending southwest to northeast in northern Virginia into Maryland. Rainfall rates have tapered with northeastward extent thanks to lower instability and PWATs, but a quick half inch to inch of rain is possible through 8 or 9AM there. Persistence is a good forecast as overcast skies and periods of showers continue to buffet Central Pennsylvania. An upper trough over Quebec and a closed low over the Ohio Valley are keeping our pattern fairly steady-state. Mid-level vort max traversing the region this morning will help focus showers across northern half of PA later this morning before drifting northeast into the afternoon. At the surface, a weak front will drift eastward and eventually stall out across the Mason-Dixon Line later tonight. Rainfall totals will approach half an inch toward the Poconos with only light amounts farther west and south. Ahead of the front, southerly winds rotating around broad high pressure over the Atlantic should help moderate temperatures today compared to the last few. Highs in the 70s areawide are +10 to +15 F higher than yesterday. Overnight, a welcome lull in the precipitation will occur as the aforementioned front settles over southern PA. Another mild night on tap with lows near 70 in the southern tier, although slightly drier air will filter in north of US-6 allowing temperatures to drop into the middle 50s. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Little in the way of changes for Days 2 through 4 as the upper- level trough over New England moves off the the Atlantic Coast Thurs night into Friday, while the moisture remnants of Helene become wrapped up in the upper low over the Lower Ohio Valley. At the sfc, a stationary front will become draped across southern Pennsylvania. This will keep the best PWATs associated with the tropical airmass south of the region, with easterly winds in control in our neck of the woods. That will mean more clouds and occasional showers with upslope flow. As Helene moves north through the Mississippi Valley on Friday, outer rainbands are progged to drift northward through PA. Showers will be efficient rainfall producers, and will have to monitor for spin, but rainfall amounts should not be too significant. Temperature- wise, the days will see temperatures fairly close to average, while clouds will keep nighttime temperatures well above average for early fall. Latest guidance indicates the potential for a period of heavier rain later Saturday night into Sunday, prompting WPC to hoist a Marginal Risk of Excessive Rainfall for that period. Still enough uncertainty in model guidance & overlap with the driest part of the CWA to hold off on getting too concerned. Most likely to be a continuation of beneficial rainfall through Saturday night, but will continue to monitor as hi-res guidance comes into range. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... 11 PM Update is mainly to nudge some PoPs upward. Big upper low creeps in from the OH Valley and still has some moisture in it despite entraining lots of continental air during the short term period. Slight ridging aloft could provide enough of a break to actually give us a entire dry day by the end of the long range. Prev... An upper-level low over the Ohio Valley will likely drift east across the Commonwealth into the beginning of next week, keeping rain chances around through at least Tuesday. Uncertainty begins to increase towards the middle of the week as a northern stream shortwave tracks near the region, bringing a cold front along with it. The timing of this feature is a little unclear with some ensemble members showing the front tracking through early Wednesday morning while others show a later frontal passage. Moisture appears to be limited ahead of the front and the best forcing looks to remain to our north, so widespread rainfall does not appear likely at this point. Most guidance shows high pressure building in behind the front which will bring drier weather and cooler temperatures. By Wednesday, expect high temperatures in the upper 50s and 60s and lows mainly in the 40s. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... 12z update... IFR conditions (low ceilings and light rain) are highly probable (80-80% confidence) at the central PA terminal sites through early afternoon (17-19z). There is medium confidence (50-60%) that ceiling bases will elevate a bit this afternoon, allowing nominal category improvements into the fuel alternate-MVFR ranges. There may even be some brief improvements to VFR late in the day (30-40% chance). By later this evening (01-05z), the expectation is that ceiling bases will lower again to categorical IFR reductions (70-80% confidence). Surface winds of 5-8 kt from the E-SE can be anticipated this afternoon, with otherwise light and variable winds less than 5 kt. Outlook... Fri...Lower ceilings are likely area-wide in the morning, then during the afternoon the best chance of showers/low ceilings will be across southern PA. Sat-Mon...The highest probabilities for low ceilings and showers should again be across southern PA. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Steinbugl/Banghoff NEAR TERM...Steinbugl/Banghoff SHORT TERM...Banghoff LONG TERM...Dangelo/Bauco/NPB AVIATION...Jurewicz