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 /08Z WEDNESDAY THROUGH SUNDAY/

Plenty of low level moisture still in place across the region. Areas east of a KBFD-KDUJ-KAOO line will likely drop down to IFR or LIFR in BR/FG for the back half of the night. Confidence is high (>70%) for LIFR in FG at KUNV as it has for the past several mornings.

The remainder of sites will see a mix between VFR and MVFR conditions overnight, with alternations between the two possible. Visibilities are expected to be mostly VFR at these sites as well.

Model guidance does indicate a slow improvement trend after 12Z Wednesday, thus have continued the trend of increasing visibilities and ceilings during the mid and late day. Winds will shift to a general southerly direction but will remain less than 8kts.

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.

CTP WATCHES/WARNINGS/ADVISORIES

None.