Slow Winds Aloft Keep Threat for Heavy Rain Looming

Very slow moving showers and isolated thunderstorms developed Wednesday late afternoon.  So slow that they prompted a Flood Advisory for Boone and Winnebago counties with nearly two inches of rain falling.  This likely isn't going to produce flash flooding, but areas that typically have poor drainage and low lying areas could experience minor flooding until late tonight.

To understand why these storms are moving so slow, we have to look up above our heads - at the jet stream.  Winds within the jet stream during the summer months typically are not that strong.  And that's why during July and August our focus shifts from the big, robust thunderstorms to heavy rain producing storms and flooding.

Without much wind in the atmosphere to push these storms through, they will just sit over one area for a while and continue to produce heavy rainfall.  We've actually seen this occur a few times over the past couple of weeks. 

While instability won't be the greatest, thunderstorms are expected to develop Thursday.  And with continued weak winds aloft those, too, could be heavy rain producing storms.  So heads up for Thursday.