Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 191851 AFDCTP Area Forecast Discussion National Weather Service State College PA 251 PM EDT Wed Jul 19 2017 .SYNOPSIS...
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Pennsylvania will be on the periphery of the subtropical ridge through the weekend. Temperatures will be above normal and there is the risk of an MCS in the ring-of-fire moisture plume. The heights are forecast to fall over the weekend into early next week suggesting cooler dry weather next week.
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&& .NEAR TERM /UNTIL 8 PM THIS EVENING/... Radar shows a broken line of showers and thunderstorms slowly working its way to the southeast and one storm was drifting through Driftwood at 2 PM. Another cell formed in Centre county and has worked its way into Mifflin County. The HRRR shows some popcorn showers about too. Most areas will be rain free but in central PA one cannot rule out a stray shower. It will be hot and humid mainly in the 80s and 90s. Instability showers should die off this evening. Nice warm humid summer evening. Good time to make a splash after dinner! && .SHORT TERM /8 PM THIS EVENING THROUGH 6 PM THURSDAY/... Nice light flow overnight. Lows will range mainly the 60s and lower 70s in the warmer spots. With dew points in the 60s and 70s there will be patchy fog forming overnight. Thicker in valleys with ponds, streams, and rivers. Fog burns off so we shall have some haze Thursday. Most guidance shows more instability and showers developing to our northwest Thursday which will drift and trigger showers near or in our northwestern counties in the afternoon and evening on Thursday. Cannot rule out a few stronger storms in northwest Pennsylvania Thursday afternoon. Chance rain best in northwest and less than 10 percent in southeast. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... The latest thinking is that upstream convective activity should evolve east-southeast across the Lower Great Lakes during the afternoon and reach PA by late Thursday afternoon into Thursday night. The details remain somewhat unclear at this time given the prospects of new storm development in advance of initial /Day 1/ MCS and potential for additional storms out ahead of outflow boundary or cold front. Global model QPF may be too far north with QPF max which is a typical bias in MCS/ring of fire patterns. The slight risk was adjusted southward to align better with projected MCS movement and axis of best instability. Showers and storms should weaken and dissipate late Thu night into Friday morning. Model data shows large scale subsidence over the area during the day on Friday with convective activity re-focusing over the Midwest/Great Lakes Friday night and propagating east-southeast toward central PA by Saturday morning. The Day 3 MRGL risk extends into west-central PA on the eastern extent of upstream organized convective zone. Over the weekend, pcpn pattern looks to reach a relative peak with max POPs based on multi-model blend. Exact timing and location of pcpn will depend on details not well resolved until the very short term time frame. Therefore the later periods will keep a 40-60 percent POP given lack of confidence in highlighting any specific areas/timeframe with concentrated pcpn potential. Medium range models generally agree that a continued/gradual weakening and east-southeast shift of the persistent central U.S. upper ridge can be expected with time, as shortwave troughing shifts slowly southeast out of the Canadian Prairie across the northeast quarter of the country by early next week. The other concern is for a several-day period of hot/humid conditions punctuated across the Lower Susquehanna Valley with blended guidance showing 2-3 days of 90+F max temps with max heat index potential approaching 100F. The heat risk remains in the HWO. A heat advisory may be needed for at least 1 day based on NDFD max HI and WPC D3-7 HI probs. The hot temperatures should be eroded from the NW with time, as the frontal boundary gradually sinks to the south in response to mean troughing developing late in the period. Above average temperatures (+5-10 degree max T departures) should trend toward mid to late July climo numbers by next Tue-Wed. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... New package showing the best chance showers/VCTS in central areas like KUNV and KIPT. At least for now as radar has a weak line north of KUNV and approaching, ever so slowly, KIPT. And cell that missed KUNV and is drifting toward, but north of KSEG. Key point some widely scattered thunderstorms about this afternoon. Otherwise a VFR kind of day. Some patchy fog overnight with MVFR and area IFR. Should burn off in the 13 to 15 UTC range Thursday. Them mainly a VFR kind of day. Increased chance showers and thunderstorms NW PA Thursday afternoon with better chance overnight into the central and southeastern areas. .OUTLOOK... Thu...AM valley fog. Cig restrictions poss NW. TSRA PSBL NW Thu aft, scattered TSRA central Mtns Thu eve. Fri...AM valley fog/cig restrictions likely NW half. Isolated TSRA. Sat...AM valley fog poss. TSRA likely. Sun...AM valley fog poss. TSRA likely north/scattered south. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Grumm NEAR TERM...Grumm SHORT TERM...Grumm/Fitzgerald LONG TERM...Steinbugl AVIATION...Grumm is the U.S. government's official web portal to all federal, state and local government web resources and services.