Heat and Instability Builds Across Mississippi River Valley

Today, much of the Mississippi River Valley and areas as far north as southern Lake Michigan are under heat advisories as temperatures are expected to exceed 90 degrees with heat indexes over 100ºF. Areas in the south, where moisture from heavy rains have saturated the ground, will experience much more intense heat indices. In addition to the heat, severe weather is threat, including flooding, damaging winds, and large hail.

A large swath of moisture is riding on the back of a region of dry air that extends from the Gulf up the East Coast. Along this axis, there is good theta-e advection pumping warm, moist air eastward.

Dry air aloft had greatly limited the vertical growth of any storms in the Illinois/Indiana region this morning. However, current radar data indicates echo tops extending beyond 40kft on developing convection near Lafayette, IN. Unfortunately there is a lack of ground data in this area. Radar image is from IWX at 3.10º.

Surface cape values are near 6000 J/kg in Central Illinois as instability is ramping up. Heavy rainfall could be dangerous for areas that have not seen much rain this past week, as flash flooding will be possible.

Once the front pushes through the Midwest, stable air will finally break the heatwave somewhat, temperatures may not drop significantly but drier air will keep things feeling more comfortable. Areas in the south may have to deal with the front a little longer as high pressure seems to be fighting the trough that is dragging eastward from a low pressure center in Canada.