7AM Day 1 Convective Outlook for Thursday, February 19. THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN ILLINOIS AND SOUTHERN INDIANA
SUMMARY
Severe thunderstorms including a few tornadoes, large hail and damaging wind gusts are expected across parts of the Midwest and lower Ohio Valley today. Elsewhere, storms may produce strong wind gusts over parts of coastal south-central California early today.
Midwest/Ohio Valley
A strong belt (80-100 kt at 500 mb) of cyclonically influenced westerlies will extend from the Southwest Deserts to the Ohio and Tennessee Valleys, with modest late-day trough amplification over the central Plains and Lower Missouri Valley. A related surface low will transition east-northeastward across the Lower Missouri Valley toward southern Lake Michigan tonight. A modestly moist warm sector will become increasingly established, characterized by mostly 50s F surface dewpoints, northward from the Mid-South across most of Illinois/Indiana into western/southern Ohio by early evening.
A steady strengthening of southwesterly winds aloft will occur today, increasingly atop/coincident with the modestly moist warm-sector boundary layer. Long hodographs will be prevalent with upwards of 50-60 kt effective shear by afternoon. Around 200-350 m2/s2 0-1 km SRH is expected to be maximized on the southeast periphery of the surface low and in vicinity of the warm front, with the favorable zone including southern Illinois, southern Indiana and northern Kentucky.
Increasing storm development should occur by late morning/midday across eastern Missouri, with maturing/increasingly surface-based storms near and just north of the I-70 corridor in southern Illinois by early afternoon. A semi-focused zone of peak severe/tornado potential may unfold generally near I-70, southward to near I-64, across southern Illinois and southern Indiana this afternoon through early/mid-evening. Sufficient forcing and boundary layer warming/mixing should allow for at least isolated semi-discrete development southward into the warm sector, and if so, relatively long-lived multi-hour supercells are plausible, with all hazards possible, but notably including heightened tornado potential, a few of which could be strong (EF2+). Given the limited early season moisture, the boundary layer will tend to become more hostile to surface-based storms and overall severe potential into mid/late evening.
Coastal South-Central California
Bands of shallow convection will continue to move inland this morning. Weak destabilization, along with moderate mean boundary-layer winds just off the surface, could allow for locally strong to damaging gusts as the front progresses southeastward.