Two Potential Rounds of Severe Weather

Two rounds of severe weather are possible on Wednesday, exactly 1 year after the tornado that swept through Sublette and the Woodhaven Lakes area.

My first note will be to say that the timing and specifics are subject to change, as we get closer to the overnight hours of Tuesday into Wednesday.

6-21-16 outlook 1
Let’s start with Wednesday morning:

An hour or two before sunrise we’ll start to see thunderstorms enter northern Illinois, and they’ll persist through the late morning hours. An organized cluster of thunderstorms that lasts for hours will bring us heavy rain with possible flooding. There’s a risk for large hail, followed by a low threat for strong and damaging wind gusts, with these morning thunderstorms.
The thought now is that those thunderstorms will push out by around 10:00AM or 11:00AM. The earlier those end, the higher the threat for a severe afternoon/evening.

Here’s why: The atmosphere will be destabilized (ripe and juicy) during this time to allow those AM thunderstorms to pop up. A large, long-lasting, cluster of thunderstorms will likely “use” much or all of that instability (juice). Once the thunderstorms end, the atmosphere can start recharging (heating back up, destabilizing) which will give some juice to evening thunderstorms. The later those morning thunderstorms last, the less time the atmosphere has to recharge, meaning the less juice available for the next round of storms.

6-21-16 outlook 2

More on Wednesday mid-afternoon through evening: A warm front should lift northward sometime in the early afternoon on Wednesday. South of that warm front, will be a warm and humid airmass (dewpoints near 70 degrees) that will be unstable. In addition to an unstable airmass, strong winds high up in the atmosphere will be exceptionally high, giving the air a better ability to spin.
*IF* we get thunderstorms to fire up in the mid-afternoon through evening, the chance of those turning severe is likely.
Time frame for the afternoon/evening round of storms is pretty wide, with the expectation to narrow it after seeing how Wednesday morning storms affect our atmosphere. Right now, be weather aware again between 3PM-8PM, with a bigger emphasis on the second half of that time frame. Thunderstorms would move east-southeastward into the Chicagoland area after that. All threats are possible with this. Large hail, a few tornadoes, and damaging wind gusts.

6-21-16 when what

Overall here’s an important note: What happens in the morning will play a very big role on what happens in the mid afternoon/evening.

There’s plenty of time to prepare instead of panic. Put fresh batteries in the weather radio, practice your safety plan, and stick with the 13 Weather Authority.

 

– Meteorologist Morgan Kolkmeyer

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This post was written by Morgan Kolkmeyer on June 21, 2016

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