textproduct: State College

WHAT HAS CHANGED

* Started mention of possible severe thunderstorms Thurs and Friday (mainly SE half of CWA) * Mentioning 100 HIs for the lower susq

KEY MESSAGES

1) Trending humid with heavy downpours and localized flash flooding possible into the weekend

2) Severe thunderstorms are possible Thursday and Friday afternoons/evenings

3) Heat index could approach 100F Thursday and Friday SE of Harrisburg

DISCUSSION

KEY MESSAGE 1: Trending humid with heavy downpours and localized flash flooding possible into the weekend

WPC continues to outlook most of the CWA in the MRGL risk of Excessive Rainfall (Flash Flooding) for the next 5 days. Seems logical since we expect the dewpoints to rise into the 70s over the S and U60s in the N and hang there for many days. PWATs seem to peak today around 2.25" in the SE. Then they don't get that high again (daily peaks of 2" in the SE, but 1.7" in the NW). A pattern shift to a more-zonal flow aloft should occur over the weekend, but a cold front and/or dry air is not in store for us.

The confidence in flooding is low due to confidence in placement of the heaviest rain being low. Certainly, the wettest places from over the weekend will sit higher on the list, and there are some hints that the SErn third or so of the area will be most at- risk for repeated shots of heavy rain. But, no flood watch are expected for today, and we'll only get a better feel for each new day as we see where the previous day's precip has been heaviest.

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KEY MESSAGE 2: Severe thunderstorms are possible Thursday and Friday afternoons/evenings

MRGL risk for severe wind gusts exist on Thurs (and likely Friday, too) over the SE half of the area per the latest SPC outlooks (new DY3 not out at press time). The shear is less than modest, but CAPE does climb into the 1000-2000 J/kg each of those aftns. However, the CAPE is long/skinny, which is more indicative of heavy rain threat. If we can get some dry air in the mid levels either day, and the small height falls on Friday can help jack up the instability and DCAPEs, any of our storms could make a strong to severe gust. ------------------------------------------------------

KEY MESSAGE 3: Heat index could approach 100F Thursday and Friday SE of Harrisburg

Just going to start to mention this possibility here in the AFD for now. The heat index does get very close to and may exceed 100 degrees using the current NBM guidance temps/dews. There is some doubt in the mind of an old forecaster, though, as he wonders if the anticipated clouds and showers/storms will keep the HI lower - even if just a degree or two which would make the difference in advy/no. The temps won't be all that abnormal, it will be the dewpoints which would take us over. At this point, we'll hold off on heat advisories.

AVIATION /07Z WEDNESDAY THROUGH SUNDAY/

Surge of low level moisture from south to north will likely bring MVFR ceilings into parts of the southern PA airspace this morning. Cigs most likely trend back to VFR for the afternoon. Best odds for a brief heavy downpour and localized MVFR/IFR visibility appears to be in the KMDT/KLNS vicinity this afternoon. Confidence is generally low regarding precip trends. Humid and stagnant airmass tonight suggests favors lowering flight cats toward MVFR into early Thursday morning.

Outlook...

Thu-Sun...Pockets of fog in the morning. Scattered showers/isolated t-storms with heavy downpours and localized restrictions.

CTP WATCHES/WARNINGS/ADVISORIES

None.