A squall line or solid line of thunderstorms is expected to develop over northern Illinois this evening. The greatest severe weather threat from these storms is damaging wind gusts of 60 to 70 mph. These storms will evolve from supercell thunderstorms that will move into northern Illinois from Iowa and Missouri this evening and then race east northeast.
Isolated tornadoes are possible with these storms as well...however the risk of tornadoes will diminsh as these storms come farther east across Illinois and as we get later through the evening.
These storms are being driven by an unusually strong storm system across the northern Plains. This storm system is winter-like in terms of its wind energy...with winds over 100 mph in the upper levels of the atmosphere. This wind energy combined with abundant moisture streaming north ahead of a cold front and high instability prompted by very warm air near the ground and colder air aloft will set the stage for explosive thunderstorms development.