textproduct: State College

WHAT HAS CHANGED

Little changes for this update.

KEY MESSAGES

1) Rain returns to the forecast late today into tonight with showers and scattered thunderstorms, concentrated across the NW half of PA. Steady, light to moderate rain Friday night into Saturday. Lingering risk for a pop up shower in the Laurels Sunday.

2) Increasing heat risk builds through the middle and latter part of next week.

DISCUSSION

KEY MESSAGE 1: Rain returns to the forecast late today into tonight with showers and scattered thunderstorms, concentrated across the NW half of PA. Steady, light to moderate rain Friday night into Saturday. Lingering risk for a pop up shower in the Laurels Sunday.

Upper level energy and a weak sfc cold front headed our way from the Ohio Valley and strong diffluent flow moving over the increasingly moist and unstable llvl environment will lead to an expanding area of showers/TSRA over Ohio and NW PA. Earlier clouds, showers and lower sfc Tds in the 50s minimized SFC- based CAPE across our region so far, but a strong uptick in convection is expected over the next 1-3 hours across areas just upstream from our CWA. This convection will move east into our Western zones mainly after 22Z where SPC's upgraded SLGT risk for SVR TSRA just nips that part of our CWA.

Rain chances will increase late this evening across the SE half of the state, but ML CAPE will be steadily diminishing there with SFC Tds struggling to climb into the 60s.

Patchy fog is possible in the valleys of the north late tonight into early Fri AM, especially if there is some notable clearing after the rain moves out.

Another system will make its way into our region with perhaps a more widespread shield of stratiform rain with embedded/trailing convection Friday night into Saturday, similar to what we saw on Monday. However there is still a great deal of model-to-model and run-to-run spread in timing and location of these convective features moving across the country, so confidence is low to medium.

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KEY MESSAGE 2: Increasing heat risk builds through the middle and latter part of next week.

A deep trough settling into the Pacific Northwest and Intermountain West this weekend will likely result in a downstream upper ridge developing over the eastern US by early next week. Blended ensemble guidance driving the prototype probabilistic Heatrisk is showing a signal for a significant warmup for Central PA to end June and start July. There is still spread in ensembles regarding the placement of the upper level ridge, but there is the potential for high temperatures to exceed 90 degrees over a large portion of the area towards the end of the forecast period (Tue-Thu). With humidity also expected to be on the rise, we may see heat index values approach 100 degrees by mid to late week, especially in the lower Susq Valley. Depending on the exact positioning of the ridge, there may also be some potential for clusters of showers and thunderstorms moving in from the northwest, but in the absence of organized convection arriving from upstream, this may predominantly be a rain-free pattern for a few to several days starting Sunday. Highest chance for convection is later in the week.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Trends tonight depict remaining storms moving into a weaker environment with only UNV, JST, and AOO at any chance of -TSRA the remainder of the night remain.Even then, confidence is only high enough (20-30%) to warrant PROB30 categories in the near future. Spotty showery activity remains more likely the remainder of the night with chances lowest at MDT and LNS.

The rain will lead to plenty of moisture to allow for fog to develop across the northern tier of the state with the highest confidence in IFR conditions after midnight at BFD. IPT may need to be watched for visibility restrictions in future TAF with some guidance having high probabilities of fog not too far north of IPT in the 07Z-12Z timeframe.

Lower cloud ceilings in the MVFR category are also likely Friday morning across TAF sites, in the wake of the rainy conditions, with highest confidence currently at BFD, JST, UNV, and IPT. Each sites most confident timing in arrival and departure of MVFR ceilings has been reflected in their 00Z TAF. After those conditions clear up by mid-morning, things are trending to VFR in the afternoon before rain showers begin to overspread the Commonwealth, leading to possible restrictions. This activity is expected to start Friday evening and night, lasting into Saturday, so be on the lookout for updated timing in future TAFs.

Outlook...

Sat...Restrictions likely in periods of stratiform rain and a few thunderstorms.

Sun...Mainly VFR with restrictions unlikely in any afternoon -SHRA.

Mon...Mainly VFR, dry conditions prevail.

Tue...Mainly VFR, dry conditions prevail.

CTP WATCHES/WARNINGS/ADVISORIES

None.