textproduct: State College

WHAT HAS CHANGED

* Severe thunderstorm watch in effect for the NW counties through 9 PM.

KEY MESSAGES

1) Strong to severe thunderstorms will roll into the west late this afternoon and evening.

2) Cold front will pass tonight cooling things off, and cooler air aloft under deep upper low will set up an unstable airmass for Sunday and Monday.

DISCUSSION

KEY MESSAGE 1: Strong to severe thunderstorms will roll into the west late this afternoon and evening.

Severe thunderstorm watch has been issued for the 3 MW counties in CTP's CWA. Thinking is that the intitial batch/cluster of storms in OH will move slowly and not arrive in Warren Co until 5 PM (21Z) or later. The watch may need to be expanded a little to the east, and even extended a little in time (esp if it is expanded) past the current exp time of 9 PM (01Z). The main severe threat today is damaging wind gusts. But, the initial storms/clusters may have some rotation to them.

Certainly worth monitoring the rainfall across tha area if the storms stay slow-moving. But, the wind field looks more linear/progressive as the night goes along. FFG in that area is 1.5-1.7"/1 hr. Not high, but also not all that low.

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KEY MESSAGE 2: Cold front will pass tonight cooling things off, and cooler air aloft under deep upper low will set up an unstable airmass for Sunday and Monday.

The first batch of storms are ahead of the main cold front which is being driven SE by a digging/deepening upper low to our NW. The front will pass through late this evening in the NW and before morning in the SE. Thunder will continue to be possible overnight as the initial storms and then the front (with any additional storms) roll through. However, the loss of daytime instability and generally poorer severe components will cause the weakening of the storms to sub-severe levels. Expect some drying to occur overnight with dewpoints lowering slightly over the NW half of the CWA. If we get some clearing, the ambient moisture will help make fog again tonight.

Temps aloft will cool substantially. Even at 8H, temps will drop 10C over the next 30hrs. The resulting instability, especially during the afternoon heating, will result in numerous SHRA/TSRA. The most-favorable conditions will be across the nrn half of the CWA Sunday where SPC has a MRGL risk for severe wind & hail. Maxes only in the 60s and a brisk W wind will make it feel much more like Sept/Oct than mid-Aug.

Similar conditions are expected for Monday with the center of the upper low still hanging around our longitude and only moving slowly poleward. The SHRA/TSRA will likely be confined to only the nrn tier of counties in PA on Monday.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Working both shifts today, so 00Z TAF set done largely already earlier this aft (18Z set), so main adjustment for the new set is for timing of showers and storms as of early evening.

Back edge to most everything is near the PA, OH border.

More information below.

Much of the area is VFR as of early aft. Still a bit of lower conditions across the far east.

Timing of showers and storms in the 12Z TAF package looks good, so will use it. Best chance for a strong storm is near the across the far northwest part of PA, where higher dewpts are and also closer to the low pressure system.

Also a coastal low will keep a chance of shower or perhaps a brief storm over the southeast.

For Sunday, went with VCSH at BFD, but dry otherwise, as wind shift line is past our area.

Outlook...

Mon-Wed...Patchy morning fog, otherwise mainly VFR conditions return early next week.

Thu...Chance of showers and storms again.

CTP WATCHES/WARNINGS/ADVISORIES

Flood Watch until 2 AM EDT Sunday for PAZ017-018-024-025.