textproduct: State College

WHAT HAS CHANGED

* Level 2 severe thunderstorm risk introduced for Tuesday (9/1)

KEY MESSAGES

1) Late summer heat+humidity to close August and open September 2) Bouts of heavy rain & severe storms possible Monday-Wednesday

DISCUSSION

KEY MESSAGE 1: Late summer heat+humidity to close August and open September

Strong upper ridge expanding east-northeastward from the south central Plains through the TN Valley into the southern Mid Atlantic and Southeast states will deliver a stretch of above normal late summer warmth and very humid conditions to close out August and kickoff September. Forecast max/min temperatures are projected to rise several degrees above the historical average Sunday-Thursday with the largest departure from normal (+10-20F) found in midweek overnight lows. The late summer heat is forecast to peak Tuesday and Wednesday with max heat indices approaching advisory levels in the mid to upper 90s across parts of south central PA. The well above normal temperatures combined with high humidity and very warm overnight lows will result in level 2 (moderate) to level 3 (major) HeatRisk values Tuesday and Wednesday. Increasing troughing across the Northeast U.S. should drop temperatures back toward seasonal climo by Friday/Saturday.

KEY MESSAGE 2: Bouts of heavy rain and severe storms possible through late week

A series of mid level impulses tracking eastward along the northern periphery of the elongated 500mb ridge will interact with anomalous moisture/instability and strong flow aloft to produce a few episodes of heavy rainfall and possible severe weather through late week. There are typical timing and amplitude differences of the smaller scale disturbances that will need to be resolved, but the overall convective signal from operational/ensemble/ML/AI guidance is supportively bullish. There is a growing signal for severe storms and heavy rain on Tuesday and Wednesday. SPC introduced a level 2 severe t-storm risk for D3/Tuesday and maintained the 15% or level 2 equivalent risk for D4/Wednesday. WPC continues to cover parts of CPA with level 1 excessive rainfall outlooks which may be refined/upgraded as the convective details become more clear and confidence in timing and location increases.

AVIATION /08Z SUNDAY THROUGH THURSDAY/

Widespread VFR (VSBYS and CIGS) noted across practically all of PA with variable amounts of mid and high level clouds drifting ESE across the Northern 2/3rds of the state early today.

Convergence axis between low level south/southwesterly flow was located to the west of Chesapeake Bay and was leading to the formation of an area of MVFR stratocu clouds that was nosing north into the Lower Susq Valley (near KTHV at 0830Z).

This area of strato cu will advect further north and impact KMDT, KCXY and KLNS during the mid to late morning hour with at least occasional CIGS AOB 3000 FT AGL (and possibly even in the 1500-2000 ft range at times). Tempo groups are currently in place at KMDT and KLNS from 11-16Z today, but may be updated to prevailing conditions per satellite and high res model trends.

Overall for today, a light sfc W/SW wind of 5-10 kts develops across Central PA. Any MVFR cigs over the Lower Susq Valley should lift/mix out by 16Z. A few SHRA or TSRA could develop later in the day, esp across northern PA as an upper level disturbance slides SE from the Great Lakes region, but most of the day should be dry.

Outlook...

Mon-Thu...Scattered SHRA/TSRA with brief restrictions possible; morning fog possible.

CTP WATCHES/WARNINGS/ADVISORIES

None.