Pre-Storm Conditions
how it happened

Early in the morning, a number of meteorologists in the department of atmospheric sciences were carefully studying various weather maps and data, trying to determine if a severe weather outbreak was a possibility. The batteries were charged, the cars were gased, and the outlook was favorable.

The primary concern was would the warm front, which was located in Missouri, push its way through central Illinois? Morning weather conditions were overcast and cool, but as the day wore on, temperatures warmed, dew points slowly climbed, and at 1:30 PM CDT that afternoon, the decision was made to drive to western Illinois and see what develops. And develop it did.

Thunderstorms began to explode throughout Iowa, Missouri and Illinois after 21Z, or 4:00 PM CDT. These storms would lead to more than 30 tornadoes in the state of Illinois that afternoon. This section briefly looks at some key weather maps which provide some insight in to why the severe weather outbreak occurred.

Last Update: 06/27/97
Low Level Warm Moist Air
Warm temperatures and increasing dew points were present at low levels.

Moisture Convergence
Significant moisture convergence was present in eastern Iowa and western Illinois.

Wind Shear
Directional and speed shear was present between the surface and 700 mb.

The Damage
Terms for using data resources. CD-ROM available.
Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.

warm moist air