textproduct: State College

WHAT HAS CHANGED

* Flood watch issued for most of central PA until 4/8PM * Severe T-storm watch issued for a portion of the LSV until 10PM * Expanded fog coverage late tonight into early Friday morning

KEY MESSAGES

1) Elevated flooding risk shifts from central into eastern PA late this afternoon into the evening

2) A few strong to severe thunderstorms remain possible in far southeast PA through early to mid evening

3) An unsettled weekend bookended by fair weather Friday and early next week.

DISCUSSION

KEY MESSAGE 1: Elevated flooding risk shifts from central into eastern PA late this afternoon into the evening

The right entrance (upper jet) ascent pattern will remain strong through the afternoon with a mature MCV moving eastward from around KAOO as of 1730TUC. This feature will provide strong dPVA to further enhance divergence/outflow aloft which should invigoration additional convection as it tracks into the Lower Susquehanna Valley later this afternoon.

Despite lack of lightning, rainfall has been efficient particularly within the MCV comma head and banded rain features extending to the northeast near the I-80 corridor. We've expanded the flood watch issued earlier this morning eastward through the mid and lower Susquehanna Valley where 3+ inch rainfall totals are possible. Combination of the heavy rain, complex terrain, and relatively saturated soil/low FFGs was also a contributing factor in the watch issuance. The nature of the flooding has been more inundation type vs. true flash flood with some reports of ponding water/poor drainage flooding, flooded basements, and a few road secondary closures.

Rain exits the eastern zones around 00Z with clouds gradually clearing out later tonight. Widespread rainfall today followed by gradually clearing conditions should allow for formation of late night valley fog which may become locally dense with vis 1/2mi or less into early Friday morning.

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KEY MESSAGE 2: A few strong to severe thunderstorms remain possible in southeast PA through early to mid evening

Severe T-storm watch #604 issued for a portion of the Lower Susquehanna Valley (LSV) until 10PM. The severe threat won't last that long, peaking in the next 1-3 hours and likely ending by or shortly after 6PM.

Previous... SPC highlighting the far southeast part of the lower Susquehanna Valley for severe watch potential (80% probability) via MCD#2052. MCV approaching that area should trigger increasing t-storm development through 4-6PM, accompanied by the risk of localized damaging wind gusts and perhaps a couple of tornadoes.

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KEY MESSAGE 3: An unsettled weekend bookended by fair weather Friday and early next week

By Friday, the aforementioned front will drift south but remain very close to the Mason-Dixon line. As such we can't rule out a spotty shower/t-storm in far southern PA Friday afternoon. However, most locations will stay dry and Friday looks like a fairly pleasant day with plenty of sunshine.

An upper trough carving out over the Great Lakes will bring increasingly unsettled weather conditions over the weekend. There is still considerable uncertainty with timing, intensity, and coverage of storms, but it is not expected to be a washout for anyone. This system will also deliver some relatively cooler air both at the surface and aloft. This setup could prove favorable for clusters of gusty t-storms with small hail both Saturday and Sunday. A cold front will move across the region Saturday and Sunday, helping focus severe weather potential. The best chance for strong storms will be west of I-99 on Saturday and then across eastern PA on Sunday.

In the wake of the cold front, the start of next week looks quite nice. A decaying secondary cold front could bring some light showers north of I-80 on Monday, but dry conditions prevail otherwise. Mostly sunny skies, slightly below normal temperatures, and lower humidity will provide some very pleasant late August weather. Upper troughing will continue to support near to below average temperatures and above average precipitation into early September.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

A 100-125 NM wide area of steady moderate to heavy rain was covering the Central and North-central Mtns, Middle Susq Valley, and Laurel Highlands at 1815Z and will continue to move steadily east at 35-40 mph.

Some breaks in the thick layered clouds across the far SE zones From KTHV to KLNS will support vertical growth of the line of low-topped TSRA heavy nearing the I-81 corridor just north of KHGR.

Used a roughly 2 hour tempo group during the 19-21Z and 20-22Z period respectively at KMDT and KLNS to cover some brief gusty wind and lower CIGS/VSBYS associated with the TSRA. Elsewhere to the North and West, steady moderate to heavy rain with IFR to low end MVFR conditions will prevail through 20Z across the west and about 22-23Z along and just SE of the Interstate 81 corridor.

For this evening, look for a brief, several hour period of mainly VFR before the light wind and moist ground from today's rain lead to the formation of fairly widespread dense fog after midnight through about 13Z Friday.

Conditions will become VFR in all areas by 14Z or shortly thereafter, with SCT flat cu topped by thin cirrus. Winds will be light and variable or light from the NW.

Outlook...

Fri...AM fog, otherwise trending VFR.

Sat-Sun...Scattered to numerous showers/t-storms likely. Breezy.

Mon...VFR returns for early next week.

CTP WATCHES/WARNINGS/ADVISORIES

Flood Watch until 8 PM EDT this evening for PAZ012-041-042-045- 046-049>053-057>059-065-066. Flood Watch until 4 PM EDT this afternoon for PAZ017>019- 024>028-033>036-056-063-064.