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 initial 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 the 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.

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

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 /06Z 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.

Showers are pivoting east and will only impact MDT and LNS for another hour or two as of 06Z. Some back end, scattered light showers have been noted too which may impact UNV and possibly IPT if they hold together.

The main restrictions tonight look to be in the form of low ceilings as high clouds move out of the area. Forecaster confidence in exact impacts is on the lower side, particularly in relation to what degree low level moisture will affect visibility. Regardless, widespread MVFR ceilings leading into IFR ceilings overnight looks to be the most likely solution at this time.

As the sun rises, current guidance favors MVFR ceilings lingering into mid-morning. Once daytime convection kicks in and cloud ceilings raise, VFR will be favored through tomorrow. Lake effect rain bands are possible in the northwest, which may impact BFD, although exact timing is uncertain. Added PROB30 to highlight best chance of thunderstorms in the afternoon. Cooling temperatures aloft behind the front and a 20+kt 850mb jet should allow for gusty westerly winds tomorrow.

Outlook...

Mon-Wed...Patchy morning fog, otherwise mainly VFR conditions return early next week with lower statewide precipitation chances.

Thu...Chance of showers and storms again.

CTP WATCHES/WARNINGS/ADVISORIES

None.