textproduct: State College

WHAT HAS CHANGED

* Slightly lower PoPs Thursday for areas north of I-80. Otherwise, no significant changes to the forecast.

KEY MESSAGES

1) Areas of fog and low clouds this morning. Relative minimum in showers and thunderstorms this afternoon.

2) Rain chances increase for the end of the week.

DISCUSSION

KEY MESSAGE 1: Areas of fog and low clouds this morning. Relative minimum in showers and thunderstorms this afternoon.

Areas of fog and low clouds have developed and will gradually dissipate after sunrise. A few slow moving showers are ongoing along a boundary that cuts across southwestern portions of the forecast area. Radar estimates show that a few localized areas in Bedford and Fulton Counties have seen rain totals as high as 2 inches since midnight, but rainfall rates have been low enough to prevent any worries about flash flooding. These showers should continue through the rest of the night, before dissipating through the morning.

Upper level flow becomes more zonal today and weak high pressure at the surface sets up over the eastern half of Pennsylvania. As a result, expect skies to become partly cloudy for the afternoon with highs in the upper 70s and low 80s. Model soundings show a relatively strong capping inversion over most of central PA this afternoon, which should limit the coverage of showers and thunderstorms. That being said, we may still see isolated to scattered showers and storms develop on the higher terrain of the Alleghenies. Any storms that do develop will be capable of producing heavy downpours, but the flash flood threat appears to be low.

KEY MESSAGE 2: Rain chances increase for the end of the week.

An upper level trough will set up over the northeastern US for the end of the week. A few weak disturbances moving through the trough will allow for scattered showers and thunderstorms to develop on Thursday, particularly over the southern half of the area. There is still some uncertainty regarding storm coverage, but any storms that do develop will be very efficient rain producers Most guidance shows precipitable water values climbing to near 2 inches along and south of the turnpike, tall, skinny CAPE profiles, and a sufficiently deep warm cloud layer in excess of 11,000 feet. This may support a flash flood threat over southern PA. Though shear is expected to be weak, there is some potential for storms to slowly organize as they move eastward through the afternoon. SPC has added a marginal risk for severe weather that covers the Lower Susquehanna Valley with damaging wind gusts being the primary hazard.

A stronger shortwave will move through on Friday leading to additional thunderstorm development ahead of a cold front. Instability looks to be limited, but storms will still have a very moist environment to work with so heavy rainfall will be possible.

Uncertainty begins to increase as we head into the weekend. Rain chances for Saturday will depend on how quickly the cold front from Friday drops south of the area. We could see scattered showers and storms if the front lingers over southern PA, but we would be mainly dry if it is quicker to slide off to the south. Sunday is looking like a mainly dry day as most guidance has the boundary well to our south.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Moist low level conditions continue to promote low clouds and visibility restrictions across many airfields this morning. High pressure building in will allow for improvement of conditions as the morning progresses. VFR should prevail by the afternoon as the subsidence and increasing sunshine scatter out the clouds which will be most prevalent in the east.

Winds will shift from out of the east to out of the south region wide by the early afternoon. These winds will remain light though in the 5-10mph range at most without much gustiness.

Scattered showers and isolated thunderstorms are expected to develop in the west, particularly in the southwest corner of our area, this afternoon. However, confidence is low (<30%) that any that form will directly impact BFD, JST or AOO for any long period of time. Any shower or t-storm that forms though carries the potential for heavy rainfall. Early signal is pointing towards visibility restrictions across the airfields late tonight (likely after 06Z) with IFR visibility confidence increasing further west. Timing and restriction amounts may be dictated by how widespread precipitation is in the afternoon.

Outlook...

Thu-Fri...Mainly dry early. Numerous to many SHRA/TSRA during the afternoon. Intermittent impacts likely.

Sat-Sun...Chance of showers and a few storms but lower chances than Thu/Fri.

CTP WATCHES/WARNINGS/ADVISORIES

None.