textproduct: State College

WHAT HAS CHANGED

Minor changes to previous forecast

KEY MESSAGES

1) Heat advisory in effect across the Lower Susq Valley and adjacent Scent PA through early this evening. Relief should be here for Sat.

2) Thunderstorms are expected to flare up this afternoon and produce damaging winds. Highest coverage of and strength of storms will be in the SErn third of PA.

3) More storms will move into PA Sunday afternoon.

DISCUSSION

KEY MESSAGE 1: Heat advisory in effect across the Lower Susq Valley and adjacent Scent PA through early this evening. Relief should be here for Sat

As expected for many days, the heat and humidity will remain high through the daylight hours today over the SE. Overall, there are just minor adjustments to the temps/dewpoints for this afternoon.

The passage of a cold front late today/tonight will usher in lower dewpoint air and make it feel much less muggy on Sat. Afternoon RH in the 35-45% range will feel refreshing after a couple of very humid days. Temps will still be hot, getting into the 80s and perhaps near 90F Sat.

---------------------------------------------------

KEY MESSAGE 2: Scattered showers and more isolated thunderstorms are expected to flare up this afternoon and create the potential for localized damaging wind gusts (mainly across the Susq Valley with respect to our CWA).

LLVL flow is broadly divergent across much of Central PA late this morning with layer clouds spreading into Wrn PA and the NW Mtns just ahead of a cold front.

There appears to be a narrow window in time and space for tsra with robust updrafts to develop and that will be mainly across the Middle and Lower Susq Valley in the 18-21Z window where HREF MUCAPE is between 1750-2250 J/KG. The convergence at the sfc is poor with nearly uni-directional flow as of the late morning. Many of the models develop few, if any, storms NW of State College - and some not even until past Harrisburg. PoPs will be a generic 30-50pct across the board today based on expected coverage.

The SPC slight risk remains over approximately the SE half of the CWA, but excludes the far NW zones. There is even a 30% chc of tstm wind dmg w/in 25sm of any given point over the extreme SE part of our CWA. That is a bit higher coverage than we usually expect on a slight risk day. Seems logical, though, with NAMNest CAPE at LNS nearing 3000J/kg, and moderate 30KTs of deep layer shear. WBZ is a little higher than ideal for large hail, so the main threat will be wind damage from increasingly organized clusters which is not much different than yesterday/Thurs. The slightly stronger wind aloft may help some of the storms in NErn PA spin a bit and yield a non-zero tornado threat there.

With storm coverage expected to be sparse over some or most of the CWA today, the risk for any downpours hitting the wetter areas of the CWA is low. So, the risk for flash flooding is minimal. Some places took 2 inches of precip yesterday without much of a blip upward on local stream gauges. Of course, the cumulative effects of repeated rainfall will likely lower FFG overall.

---------------------------------------------------

KEY MESSAGE 3: More storms will move into PA Sunday afternoon.

After the drier Sat, the flow backs and the more-southerly flow brings more-humid air back into PA. The mugginess will be noticed the most in the SE, with the Td just nearing 60F in the aftn. A very narrow jet buckles just a little and provides sufficient dynamics for another afternoon and evening round of severe thunderstorms. Arrival looks mid-late aftn NW with the storms crossing the CWA and exiting to the SE by 10-11PM. Some storms are possible out ahead of the front associated with the upper dynamics. The next visit from organized storms will likely not be until at least mid week (Thurs).

AVIATION /15Z FRIDAY THROUGH TUESDAY/

Bkn-OVC deck of stratocu was streaming quickly ENE into the Allegheny Plateau region of NW PA with higher based stratocu entering the Laurel Highlands. Across the Central Mtns and Susq Valley, widespread VFR will continue through much of the rest of today as the aforementioned area of clouds breaks up breaks up in the drying downslope flow and more pronounced llvl ridging.

Have some VCSH in most of the TAFS later this afternoon, but even that convective development is looking less likely attm.

A break on Saturday, but a stronger cold front on Sunday will bring the potential for more strong storms on Sunday.

Outlook...

Saturday...Mainly VFR.

Sunday...VFR favored early, with restrictions possible as FROPA brings chance of -SHRA/-TSRA later in the day.

Monday...Additional scattered -SHRA and associated restrictions possible.

Tuesday...Still a slight chance of showers and storms.

CTP WATCHES/WARNINGS/ADVISORIES

Heat Advisory until 8 PM EDT this evening for PAZ036-057-059- 063>066.