textproduct: State College

WHAT HAS CHANGED

* Issued Heat Advy for the far SE * Mentioning +RA and gusty winds for the storms today * Sunday may be rain-free

KEY MESSAGES

1) Staying humid with heavy downpours and localized flash flooding possible through at least Saturday

2) Severe thunderstorms are possible today and again Friday afternoon/evening

3) Heat index will reach 100F in the far SErn counties today

DISCUSSION

KEY MESSAGE 1: Staying humid with heavy downpours and localized flash flooding possible through at least Saturday

Sfc remains unchanged from yesterday with very humid (dewpoints 70-75F) air in place and a high off the coast. The high will move a little today and allow the sfc wind to be more from the W than S/SW as it was yesterday. That will make no difference to the dewpoints, though, with upstream values very similar. The deep layer moisture (PWAT) will be just the slightest bit lower, though, mainly in the W - with 2"+ amounts holding over the E. Also, the flow aloft will be a little more progressive with storm motions about 260 (from the W to the E) at 30 MPH. We still are low on confidence of the placement of the heaviest of rain. It didn't rain heavily in the SE Wed, and that is where the best signal for heavy rain seems to be today. FFG is lowest in the Laurels and also in a stripe from Lewistown up to LaPorte, and higher elsewhere. At the same time, the initial storms will probably fire up on the Alleghenies where they did have the heaviest rain yesterday. Consensus among local offices is that we don't have enough to compel us to post any flood watches with this forecast package.

The flow aloft does get more zonal (W-E) Sat which should keep any storms moving along a little faster. Thus, the flooding threat may also decrease despite a continuation of high sfc dewpoints. The case for flooding concerns for Sat are mainly thanks to an accumulative effect over the previous days. Sunday actually looks like we may be rain-free with slightly lower dewpoints, but that is a trend at this point and not a certainty. As the flow becomes faster aloft for next week, we will see multiple chances for showers and thunderstorms.

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KEY MESSAGE 2: Severe thunderstorms are possible today and again Friday afternoon/evening

Deep moisture will make some tall storms today and the modest 30 kts of deep layer shear might be enough to make a severe gust or two. The higher threat is SE of an AOO-UNV-IPT line. The 5H heights will fall on Friday. A shortwave trough looks like it will roll overhead late in the day/evening, too. The PWATs stay 1.75" W and 2.10" E, and the cooling mid levels could help grow the storms and perhaps give them more of a chance to become severe vs today when we'll have less upper forcing/support. SPC MRGL risk for damaging wind gusts covers generally the same locations today and Friday. Depending on timing of the next shortwave from the west, Sat may be dry (esp E), but Sunday holds a better chc for dry weather. A very active/progressive upper flow next week will keep it unsettled with near-daily chcs for SHRA/TSRA. ------------------------------------------------------

KEY MESSAGE 3: Heat index will reach 100F in the far SErn counties today

The very high (70-75F) sfc dewpoints will keep it HH&H at least through Sat. Today will probably hold the highest heat index values. Better sunshine today in the SE will probably boost the temps 4-6F over Wed. The guidance has been consistent painting temps and dews sufficent to make HIs around 100 SE of Harrisburg, with the highest possibility of 100+ nums in Lancaster and Lebanon counties. Went with a heat advy for there through 8 PM. Friday will probably just 1-2F lower on HI, so we'll keep the advy for today at this point.

AVIATION /07Z THURSDAY THROUGH MONDAY/

Radar trends indicate current shower activity will continue to diminish. MVFR to VLIFR restrictions expected through daybreak in fog and low clouds. Expect improving trend to VFR by mid morning with VFR prevailing throughout most of the afternoon and evening. Thundershowers with heavy rain will likely result in localized restrictions for short periods most likely in the 18Z Thu to 03Z Fri window. We continue to account for this via PROB30s. Similar setup into the overnight/early morning Friday period with restrictions likely due to fog pockets and low clouds.

Outlook...

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

CTP WATCHES/WARNINGS/ADVISORIES

Heat Advisory from noon today to 8 PM EDT this evening for PAZ059-066.