2PM Day 3 Convective Outlook for Saturday, July 19. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ROUGHLY FROM IOWA INTO ILLINOIS AND INDIANA
SUMMARY
Corridors of strong to severe storms are expected from the northern and central High Plains to the Mid-Mississippi and Lower Ohio Valleys on Saturday.
IA/IL/IN
Model QPF differences aside, the overarching theme is for a large area of strong instability to develop near a stalled front from southern IA/northern MO into IL and IN Saturday afternoon with mid 70s F dewpoints. This will exist beneath the southern fringe of perhaps 40 kt west/northwest midlevel flow, and the combination of strong instability and favorable deep-layer mean winds will favor corridors of severe storms with damaging winds. Shear may also favor severe hail, and even a few supercells given such large CAPE over IA/IL/IN. The risk area will likely be adjusted in subsequent outlook cycles as the event nears.
High Plains
Modest westerly midlevel flow of 30-40 kt will exist over the northern High Plains, ahead of a broad upper trough over the Pacific Northwest/northern Rockies. Cool midlevel temperatures will also exist, steepening lapse rates. Strong heating is likely within a surface trough from eastern MT southward across the High Plains, with a ribbon of 1500-2000 J/kg MUCAPE wrapping northwestward around a MN surface high. Cells capable of hail and localized severe gusts will be possible, and a severe MCS is not out of the question overnight into ND as the low-level jet increases. Greater probabilities may be required in later updates.