textproduct: State College

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

1) Periods of rain and breezy conditions today as Post-Tropical Cyclone Isaias impacts the region

2) Warmer and more humid next week with a couple rounds of rain showers possible Tuesday and again late in the week

DISCUSSION

KEY MESSAGE 1: Periods of rain and breezy conditions today as Post-Tropical Cyclone Isaias impacts the region

Steady rain will continue today into the late afternoon. PW values will peak around 18z today in the 1.50-2.00" range. Rain will begin transitioning to a more convective rain shower regime this evening. As the remnant sfc low from Post-Tropical Cyclone Isaias makes its closest approach this evening, it could bring enough elevated instability to increase thunderstorm potential for areas south of Interstate 80. Highest chance for thunder will be across the Lower Susq Valley. With a sfc inversion still in place at the time, severe weather is not expected. However, SPC does draw a MRGL risk for severe weather just south of the Mason-Dixon line.

Total rainfall is expected to range from 1.50-2.50 inches for most locations south and east of the I-80/I-99 corridor, with a roughly 30% chance of over 3 inches for locations along the southern tier, particularly if training/pivoting convective elements develop this evening. However, we continue to believe there will not be any significant flooding. Rainfall rates will not be particularly high for a majority of the event, and the recent dry spell will also provide a cushion. However, localized minor flooding can not be ruled out in the south and east.

Expect gusty winds in the tightening pressure gradient between the post-tropical low and departing high in the Gulf of Maine. Max gusts in the 35-50 mph range are expected in the Laurel Highlands particularly along and to the west side of the highest ridgetops (downslope wind from the southeast). A Wind Advisory remains in effect for Cambria and Somerset counties.

KEY MESSAGE 2: Warmer and more humid next week with a couple rounds of rain showers possible Tuesday and again late in the week

Warmer and noticeably more humid to start next week. Max temps on Tuesday are forecast to peak 10-15 degrees above the historical average for mid October with highs in the 70-80F range. Improving weather conditions can be expected Monday as the remnants of Isaias exit the Mid Atlantic. Rain chances on Tuesday appear to be maximized over the northern tier where a shortwave aloft and sfc cold front (infused with moisture from TS Rachel?) streak eastward from the Great Lakes. Another period of rain is possible later next week, but there is low confidence in the timing of the front.

AVIATION /07Z SUNDAY THROUGH THURSDAY/

Ceilings gradually lower from south to north through the night, though most sites should remain VFR through at least 06Z. After that point, rain will begin to move in from the southwest ahead of the remnants of Isaias. The rain has already reached JST and AOO and will overspread the rest of Central PA through early morning. Ceilings will initially fall to MVFR as rain begins, but quick deterioration to IFR is expected for all TAF sites.

IFR conditions should persist through the rest of the TAF period with a steady, soaking rainfall continuing for much of the day. As the rain tapers off during the evening, model soundings suggest that we will see enough instability develop for some lightning to occur near MDT and LNS. A PROB30 for TSRA has been added for MDT and LNS. Confidence is increasing on a few of these storms late tonight having enough instability to produce lightning.

Strong winds aloft will create some concern for LLWS tonight, particularly at BFD and JST. Periods of wind shear are possible farther to the east as well, but confidence is a little lower than it is for the western TAF sites. The potential for these winds to mix down to the surface is uncertain, with model soundings suggesting that relatively stable conditions should limit gusts to around 25 knots for much of the day on Sunday. The best chance for gusts stronger than that (potentially up to 35 knots) will be late tonight into early Monday morning at JST.

Outlook...

Mon...Partial clearing.

Tue...VFR favored, though a FROPA may bring restrictions in -SHRA. AM fog possible.

Wed...AM ceiling restrictions possible from post-frontal stratocu, with VFR otherwise favored. Slight chance of -SHRA due to lingering moisture behind front.

CTP WATCHES/WARNINGS/ADVISORIES

Wind Advisory until 2 PM EDT this afternoon for PAZ024-033.