textproduct: State College

WHAT HAS CHANGED

* Level 1 excessive rain risk expanded to all of CPA for today * Cooler temperature moderation next week

KEY MESSAGES

1) Very humid with locally heavy rainfall possible this afternoon

DISCUSSION

KEY MESSAGE 1: Very humid with locally heavy rainfall possible this afternoon

Highly anomalous moisture for this time of year (NAEFS mean pwat values near climatological maximum percentiles) pooling around the periphery of subtropical high over the southern Plains and lower MS Valley will interact with a surface cold front moving slowly south/southeastward from the lower Great Lakes to produce periods of showers and a few locally heavy thunderstorms across Pennsylvania later today. 17/00Z HREF indicates the potential for spot rain amounts of 2-3 inches. It's very likely that most of central PA picks up some rainfall by tonight. However, we do not anticipate an all-day rain/washout. Cloud trends remain a tough call with early morning convection over north central PA, but fcst instability this afternoon across south central PA will be more than supportive for thunderstorm development. SPC continues to maintain a general (non-severe) convective outlook for today which is likely due to the lack of deep layer shear (displaced farther to the north) and poor mid level lapse rates (very moist, tall/skinny soundings with warm cloud depths greater than 10kft).

Another taste of Fall is on the way for the end of the week with noticeably cooler and much drier/less humid air poised to return behind the front (Td crashing into the 40s/50s). Expect a crisp and cool overnight Friday into Saturday morning with some upper 30s possible across the northern tier. Dry/fair wx conditions are forecast to start the weekend and last through the day on Saturday followed by periods of potentially heavy rainfall Saturday night through early next week. Both NAEFS and ECMWF SATs show at least 90th percentile PWs returning the the region which is supportive for at least a marginal excessive rain signal. NBM temps have also cooled/moderated quite a bit Mon-Wed with most locations struggling to exceed 70F for daytime highs.

AVIATION /06Z THURSDAY THROUGH MONDAY/

Generally VFR conditions at each forecast airport through the remainder of the evening hours; however, isolated -SHRA of varying intensity are moving northwest to southeast over lower central PA. This initial batch of -SHRA will dissipate as the sun sets.

Areas that did see a shower today will have the likelihood (>50%) for BR or FG toward sunrise lasting for a few hours. A cold frontal boundary will cross the region on Thursday, bringing a chance of -SHRA and MVFR ceilings and visibility. As the front passes through during the late afternoon, winds will shift to the northwest and precipitation will end.

Outlook...

Fri-Sat...valley fog in the morning; otherwise VFR.

Sat night-Monday...periods of rain and sub-VFR likely.

CTP WATCHES/WARNINGS/ADVISORIES

None.