12AM Day 1 Convective Outlook for Sunday, August 24. THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF NEW YORK/PENNSYLVANIA AND FROM EASTERN COLORADO TO WESTERN OKLAHOMA
SUMMARY
A few storms may reach severe thresholds from eastern Colorado into western Oklahoma this afternoon and evening. Scattered strong-severe storms are possible across portions of Pennsylvania and New York. Hail or wind are the expected risks.
NY/PA
Early-morning satellite imagery depicts a strong upper trough over ON/Great Lakes, shifting east-southeast in line with latest model guidance. Associated surface front is forecast to advance into western NY/PA by early afternoon before shifting into central portions of these states by 25/00z. Modest boundary-layer heating is expected to aid destabilization ahead of the front and convective temperatures are expected to be breached around 20-21z; although, deep-layer lapse rates are not expected to be particularly steep (0-6km values around 6.5 C/km). While CAMs support this with scattered frontal convection developing around mid afternoon. This activity could generate locally strong winds, and perhaps some hail. Main risk will be during the mid afternoon into early evening before the boundary layer cools after sunset.
Eastern CO to western OK
Eastern periphery of Great Basin high will flatten as northwesterly flow becomes firmly established along the back side of Great Lakes/OH Valley trough. At the surface, pronounced surface anticyclone will settle into the northern Plains, ultimately forcing the leading edge of more continental air into the southern Plains by the end of the period. Net take is a corridor of low-level warm advection will become established from southern WY into western OK - coincident with northwest-southeast frontal orientation. It appears a few weak disturbances will top the ridge and dig southeast toward the southern Plains. Each of these features should encourage a response in the LLJ, which will aid convective development. Elevated convection may be ongoing at the start of the period across western NE into northwest KS. A substantial cluster/MCS should propagate southeast with renewed development later in the period. Rain-cooled boundary layer will ensure stronger heating is focused across southeast CO into western OK. Primary concern for isolated severe will be near this zone of stronger heating/instability. Hail and wind may accompany this more robust convection.