Area Forecast Discussion
Issued by NWS State College, PA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KCTP 292141 AFDCTP Area Forecast Discussion National Weather Service State College PA 541 PM EDT Mon May 29 2017 .SYNOPSIS... A trough of low pressure will stall out over central and eastern PA late today, before retreating back into the Central Mtns tonight. Another cold front will push toward the region Tuesday and combine with the lingering boundary to produce numerous showers and scattered afternoon thunderstorms, some of which could contain gusty winds and hail. Low pressure at the surface and aloft will stay centered near James Bay Canada through the rest of the week. This weather feature will supply a period of slightly cooler than normal temperatures, and push a few additional weak cold fronts through the commonwealth accompanied by scattered showers and perhaps some isolated afternoon and early evening thunderstorms. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Weak surface front remains stalled over the Susquehanna Valley late this afternoon with partly to mostly sunny skies and a light to mdt westerly breeze across the Central and Western Mtns of PA. To the east of the boundary, cool and cloudy airmass with low stratus below 1000 ft agl will prevail with temps only in the low-mid 60s. Maxes elsewhere will be mainly in the 70s, with mid-upper 70s likely in the central and southern valleys to the SE of a KAOO to KUNV line where the llvl westerly downslope flow and heating will be maximized. Differential heating along the western edge of the cloud boundary across the Susq Valley will lead to a narrow ribbon of enhanced cape and moisture convergence which will help to produce isolated-scattered showers and isolated low-topped TSRA per the latest 18Z HRRR. However, the model appears to be overestimating llvl cape and convection at this time, thanks to the presence of at least weak larger scale subsidence aloft - beneath the right exit region of a 105 kt upper jet. Any convection will drift to the east and should greatly weaken within 20-30 miles east of the stalled out llvl boundary. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... Brief ridging will allow any popcorn sprinkles and light showers to clear over the western two-thirds of the CWA this evening, and residual moisture may lead to areas of fog, especially in the central valleys. The low level moisture and low stratus deck AOB 1000 ft AGL will push gradually westward across the Central Mtns and West Br Susq Valley and stay intact through early Tuesday. Mins tonight will dip into the 50s for most, as the dewpoints will be the bottom limit. A separate, weak sfc trough will be pushed into the area from the northwest tonight. 8H temps fall a bit over the NW. Heights fall just a little, too, so some precip is possible before sunrise Tuesday over the northwestern third of the area, but it should be light. The trough begins to catch the stalled trough over the eastern counties. The southerly or southeasterly wind will yield good convergence and will crank up some showers and thunderstorms. Have painted high POPs for the area, but the amount/severity of destabilization is in question with the clouds in the NE early in the day. NAM cranks out 1500joules of CAPE and LI drops to -2 or so in the mid-day and aftn on Tues. SPC marginal Risk of svr wx for Day 2 (Tues) is painted across our eastern half, focused on the peak heating time. Will continue to mention this in the HWO. Max temps across the region will range through the 70s, with the warmest readings once again in the scent mtns where 78-80F readings should occur. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... The long term period begins with a good consensus on the location and shape of the large upper level low over southern Canada. That low will dominate the weather pattern this week into next. As the low rotates it will bring successive short and long wave troughs through the Mid Atlantic region. These troughs will bring the possibility of precipitation, mainly Wednesday and Friday afternoon. This upper level low will also bring cooler northwesterly flow into central PA. That flow should keep temperatures around, to slightly below, normal. The next chance for significant precipitation will be Friday night into Saturday as that upper level low progresses eastward. The models begin to diverge on the position, timing and strength of the system. This decreases confidence. However, all models show a boundary that should set up through the keystone state. The main question is when will it progress through and how much moisture will be available for QPF when the corresponding cold front moves through Saturday. Current GFS brings precipitation through Saturday where the EC brings largest QPF Sunday. && .AVIATION /22Z MONDAY THROUGH SATURDAY/...
-- Changed Discussion --
Widespread sub VFR cigs will be difficult to clear across the far southeast late this afternoon, and if so, it will be only for a brief few-svrl hour period. Llvl easterly flow of 5-10 kts will likely persist over, and to the east of the susq valley with MVFR to IFR cigs and VFR to MVFR vsbys in light fog/hz. Adjusted 21Z TAFS. Have a lone thunderstorm to the south of MDT, should stay well south of the airport. Earlier discussion below. Sct-bkn VFR stratocu and cu will occur across the western two thirds of the state thanks to a drying, light to moderate westerly llvl wind. Depending on how much clearing occurs/remains this evening, widespread fog formation is possible region-wide tonight. Later on, expect the stalled out boundary across the Susq Valley to drift westward back to the Allegheny Front (KAOO, KUNV and KIPT) by...or shortly after 04Z Tuesday. .OUTLOOK... Wed...Chance of showers. Thu...No sig wx expected. Fri...Chance of showers and thunderstorms. Sat...Still a chance of showers and thunderstorms.
-- End Changed Discussion --
&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Ceru/Martin AVIATION...Lambert/Martin is the U.S. government's official web portal to all federal, state and local government web resources and services.