UPDATE: Tuesday Night Storm Threat

2:10am Update: Severe Thunderstorm Warning continues for DeKalb, southern Boone and McHenry counties until 3am and for Whiteside county until 2:30am.  Wind gusts close to 60-70 mph are possible with these storms.

 






12am Update: Severe Thunderstorm Warning issued for Green and NW Rock counties in Wisconsin until 1am.  Wind gusts to 60 mph are going to be the primary threat.  The storm is moving to the southeast at 65 mph.

9:45pm Update: A Severe Thunderstorm Watch has been issued for most of Northern Illinois and Southern Wisconsin until 5am Wednesday morning.  Biggest threat with thunderstorms that move through will continue to be strong wind gusts.  Timing hasn't changed with these storms.  Still looking like storms between Midnight and 4am.

9pm Update: Storms upstream over SE Minnesota continue to hold their own with regards to strength.  As a result, a severe thunderstorm watch will likely be extended over Wisconsin, Iowa and Illinois within the next hour.  Biggest threat continues to be damaging wind gusts.  Timeline for storms will be in Southern Wisconsin by Midnight and Northern Illinois between Midnight and 3am.

Read the technical weather discussion from the Storm Prediction Center here.



Tuesday evening will remain quiet but it's once we get closer to Midnight that we could have some problems.

Thunderstorms over Minnesota Tuesday afternoon quickly turned severe feeding off of high instability over the Upper Midwest.  Severe Thunderstorm Warnings and even a couple Tornado Warnings have been in place as individual thunderstorms now begin to merge and develop into a cluster of storms. 

While we'll lose some of our instability when the sun sets, I think we will have just enough to be able to sustain the storms over Minnesota as they

move closer to Southern Wisconsin and Northern Illinois.  And that's why the Storm Prediction Center has included SW Wisconsin and NW Illinois under and 'Enhanced Risk' and the rest in a 'Slight Risk'.  The storms over Minnesota are beginning to take on a bow shape, meaning damaging winds will likely become the greatest threat over the next couple of hours for Northern Iowa and Southern Minnesota.

The image to the left indicates where the highest CAPE values, or energy, resides in the atmosphere.  Right now, the greatest instability is over Iowa where they've seen more sun today and dew points are very high.  Further east over Wisconsin and Illinois there is a decent amount of instability, but it isn't as high.  However, I do believe we will keep just enough to help sustain thunderstorms between Midnight and 4am.

If the storms over Minnesota hold their strength strong, possibly damaging, winds are going to be the biggest threat.  Very heavy rainfall would also be a concern.

The majority of our models indicated a line of strong thunderstorms moving through around or shortly after Midnight.  We'll continue to monitor development upstream for the potential for strong winds late tonight.