It's been a soggy and damp Tuesday afternoon with temperatures most of the day in the 50's. It was only as of late afternoon that the high in Rockford was able to break the 60 degree mark. South of Rockford towards Rochelle and DeKalb temperatures have warmed into the 60's and Sterling has even reached the low 70's. The reason: a warm front. That front stayed south of us the majority of the afternoon keeping the steady rainfall over most of Northern Illinois.
Skies have started to clear south of Rockford (where the highs are in the 60's and 70's) along a warm front. The air mass along and south of the warm front has become slightly unstable and as a result showers and thunderstorms have begun to bubble up. While the atmosphere is not suggestive of severe weather, there have been a few funnel clouds reported near Clinton, IA and Kewanee, IL. These are not the types of funnels that turn into tornadoes, but it's interesting to learn how these exactly develop.
Where the breaks in the cloud cover have occurred instability at the surface has gone up. Surface winds south of the front are from the south, while north of the front winds remain from the east. This change in direction in just a short distance creates very weak low level wind shear. With an upper level low close by there is enough energy in the atmosphere to generate those showers/storms that are now developing on radar. As these showers develop and move into locations in the environment that are
experiencing weak wind shear, weak funnel clouds develop. Very rarely do these funnel clouds reach the ground and cause damage, and they usually only last for a short amount of time. The threat for those will last through sunset with drier skies into the night.
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