textproduct: State College

WHAT HAS CHANGED

* Storms now firing up on the high terrain east of IPT. Changed timing of precip and mentioned +RA/gusty winds

KEY MESSAGES

1) Isolated to scattered showers and thunderstorms today, mainly south of Interstate 80. Sunday will be mostly dry.

2) Hot and humid pattern set to return for the middle of next week

DISCUSSION

KEY MESSAGE 1: Isolated to scattered showers and thunderstorms today, mainly south of Interstate 80. Sunday will be mostly dry.

Radar trends are verifying earlier forecasts and yield high confidence in CAM projections of isolated to scattered showers and thunderstorms over most of the area with the highest concentration and frequency over the eastern third of the CWA. Latest HRRR/HREF progs show convection lingering longer than NBM hourlies have them doing. Expect the timing to still be centered between now (2 PM) and sunset. However, we'll add a small amount to PoPs between 00-03Z to bend to the trend.

Previous discussion: With yesterday's cold front still pushing slowly south across the Commonwealth, we'll likely see another round of showers and thunderstorms fire up late this morning and persist into the early evening hours. However, the threat for torrential downpours does not appear quite as widespread or intense as yesterday. The main area will be south of Interstate 80.

Max SBCAPE is progged in the low 1000s J/kg with fairly weak NW mean flow around 15 kts in the cloud bearing layer. Given the weak flow, initiating boundaries may come from a variety of sources including terrain features, differential heating boundaries (morning fog may create some of those), and the cold front itself. HREF and REFS members have picked out the higher terrain in Schuylkill County as one such terrain feature that may focus convection initiation, with a swath of locally 1+ inch of rain coming off the high terrain and stretching southeast - a plausible solution that we'll have to watch for. Dry air advection behind the southward moving cold front will gradually bring an end to convection from north to south this evening. Fog may develop in the river valleys tonight as temps fall into the 50s and low 60s.

With drier air in place on Sunday and building high pressure providing a subsidence inversion above the boundary layer, Sunday is still on track to be a mainly dry day. However, a stray shower can not be ruled out particularly over the Laurel Highlands or near the Poconos.

---------------------------------------------------------------

KEY MESSAGE 2: Hot and humid pattern set to return for the middle of next week

Dry conditions are expected to prevail for the first half of the week with a strong ridge expected to develop over the middle of the country. Increasing heat/humidity is forecast across central Pennsylvania although there remains some uncertainty with respect to how warm temperatures and/or humidity get across the region. Current forecast favors the hottest temps returning Tue to Thu with highs 85-95F and max heat index 90-100F, potentially rising above 100F on Wednesday. Rain chances increase into the latter half of the week.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Morning radar is free of precipitation returns threatening TAF sites. Lifting of cloud ceilings and increase to P6SM visibilities is expected over the coming hours as the sun induces low level convection. There may be some intermittent restrictions to IFR/MVFR has this process occurs.

Showers and thunderstorms today look lower in coverage than in previous days. Upper level forcing and a relatively weaker front doesn't support widespread thunderstorm activity. Regardless, a moist airmass in place to the south of the front means any storm that does pop up could carry heavy rain and visibility restrictions as a result. Chances of this occurring look highest at MDT and LNS.

In the wake of this convection, high pressure begins to build in during the overnight. The suppressive activity will begin to clear out clouds to begin a less active stretch of weather with mostly VFR conditions say for any patchy fog that develops in the late nights/early mornings.

Outlook...

Sun-Wed...Mainly VFR with areas of late night/AM fog.

CTP WATCHES/WARNINGS/ADVISORIES

None.