Thunderstorms quickly developed Wednesday afternoon producing anything from one to two inches of rain, along with pea to quarter sized hail. While the severe threat is low this evening, there is quite a bit of instability and energy in the atmosphere. One way meteorologists measure the energy is by looking at CAPE values - 'Convective Available Potential Energy'. This afternoon, CAPE values were over 3,000 J/KG. Anything over 1,000 J/KG is considered high. So as these thunderstorms developed they had a lot of energy to feed off of to help them grow quickly. What has kept most of them mostly below severe limits has been the lack of wind shear in the atmosphere. Winds aloft are very light - which is why there have been reports of minor flooding and is the reason for the very slow movement of these storms.
A Flood Advisory has been issued Winnebago, Ogle, NW DeKalb and NE Ogle counties until 7pm. The Flood Advisory was also extended southward to cover most of DeKalb and Ogle counties, and the northern half of Lee County until 8:15pm. The majority of these storms will remain below severe limits, but heavy rain, small hail and brief strong winds will be possible with any storm that does develop. Storms should become less in coverage after sunset Wednesday evening.