textproduct: State College

WHAT HAS CHANGED

Level 2/5 severe t-storm risk shifted to the west out of Warren County

KEY MESSAGES

1) Severe thunderstorms capable of damaging winds and heavy rainfall remain possible through Tuesday

DISCUSSION

Unfortunately, the pattern into midweek does not lend itself to a high confidence forecast given the growing uncertainty details surrounding the evolution upstream convective activity.

KEY MESSAGE 1: Severe thunderstorms capable of damaging winds and heavy rainfall are possible this afternoon through Tuesday

Convection has been percolating across CPA from late morning through early afternoon. While much of this activity has been fairly shallow and transient so far, a few stronger cores have briefly pulsed to near severe limits before decaying. Weak deep- layer wind shear will continue to modulate the overall storm intensity and longevity; however, steady diurnal heating through broken cloud cover (with smoke aloft) has allowed temperatures to warm into the mid 70s-80s within a relatively moist air mass. This heating/mixing has allowed low-level lapse rates to increase to around 8 to 8.5 C/km, which is favorable for isolated downbursts capable of producing strong to damaging wind gusts (most likely 40-60 mph). GOES imagery shows several deepening towers and cumulus clusters, hinting that thunderstorm coverage will continue to increase - especially along a subtle surface trough/weak front draped across the region. The potential for damaging gusts should increase on the margin in tandem with thunderstorm coverage, but the overall threat should remain sufficiently localized and transient to preclude watch issuance per SWOMCD #1765 (5% probability). Storm motions have also been fairly progressive so far from NNW to SSE which should limit any localized flooding concerns within brief heavy downpours.

Timing and placement uncertainty grows heading into tonight with continued CAM variability concerning downstream development/propagation of Great Lakes/Ohio Valley MCS activity. The main shortwave does appear to reach CPA by Tuesday morning. The decaying? MCS or related feature and associated cloud cover could dampen severe risk into the afternoon. Hires guidance seems to suggest an eastward shift in the greatest svr/FF risk as the trough deepens over the northern Mid Atlantic. Some heavy rain potential will linger into Wednesday as the slow moving upper low pivots from northeast PA toward southern New England. Storm totals could exceed 2-3 over some parts of the northeast CWA by Thursday morning.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Radar trends suggest increasing t-storm coverage through the afternoon and will continue to utilize PROB30s for brief localized terminal restrictions. Low confidence in timing of showers and storms (lowering of flight cats) later tonight into Tuesday given high uncertainty with upstream tstm evolution. There is a fairly good signal for at least MVFR early Tuesday.

Outlook...

Tue-Wed...Restrictions likely SHRA & TSRA.

Thu-Sat...Improving conditions into late week. Patchy AM fog.

CTP WATCHES/WARNINGS/ADVISORIES

None.