textproduct: State College

WHAT HAS CHANGED

* Excessive rainfall outlook shifted southwestward Thursday

KEY MESSAGES

1) Humid with additional showers/thunderstorms possible into late week

2) Seasonably cooler and less humid Friday and Saturday

DISCUSSION

KEY MESSAGE 1: Humid with additional showers/thunderstorms possible into late week

Parade of convective complexes and associated cloud cover has effectively shut off precip across western PA for the time being. Farther to the east, widely scattered thunderstorm development is expected through the rest of the afternoon with an isolated threat for damaging wind gusts. More sunshine beneath a cirrus canopy has driven temps into the mid 80s supporting modestly steep low level lapse rates. Water loading higher pwat air would also be supportive of localized downbursts. This area will be monitored, but the probability of a watch issuance is 5% per MCD #1928.

Confidence in how the precip pattern evolves from west to east from the Ohio Valley later tonight remains quite low. This is due in a large part to high variability in the CAM signals. We will let the flood watch for Somerset County ride for now and allow evening shift to assess radar/model trends. Patchy fog is likely to form late tonight into early Wednesday morning.

Uncertainty only grows with time through midweek. Slow moving frontal boundary will continue risk of showers and heavy thunderstorms through Thursday; however tomorrow (8/12) appears to mark a nadir in both severe storm and flash flood risk.

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KEY MESSAGE 2: Seasonably cooler and less humid Friday and Saturday

Comfortably cooler and noticeably drier (less humid) air accompanies seasonably strong/Canadian high pressure building southeast from the Upper Midwest Friday night through Saturday. Below normal pwats will facilitate pleasant days and crisp nights (40s and 50s most locations Friday night/AM Saturday.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Mostly VFR conds as of 18z Tue, with the exception of some MVFR cigs across the western airfields associated with an old MCS and some lingering low clouds to its north. Much of the strong convection this afternoon is missing PA, passing to the south, but additional showers and storms are expected to develop this afternoon and early evening along a boundary across the northern tier. Additional storms are possible overnight as the ring of fire pattern remains active. Some fog is also possible overnight, especially at BFD (50 pct chc) as well as low cigs esp at JST (60 pct chc of IFR or lower). Conditions will trend towards VFR areawide by early Wed afternoon, before isolated SHRA/TSRA develop again.

Outlook...

Wed/Thu...Scattered showers/storms mainly across the southern Tier of PA. Restrictions possible.

Fri...Mainly VFR. A few showers or storms possible over southwestern PA.

Sat...Mainly VFR.

Sun...Restrictions poss in SHRA/TSRA.

CTP WATCHES/WARNINGS/ADVISORIES

Flood Watch through late tonight for PAZ033.