Severe Weather This Evening

Originally I had planned to update you on the overall situation of strong thunderstorms over northwestern Iowa and southwestern Minnesota - but that changed just before our 6pm show. We saw a strong storm develop over NW Iowa with some strong signs of rotation, and now we can't help but talk about that system. Look at this image below, and I will explain what the different elements mean as we go... but this was a shot of the storm at about 6:05pm central time:

(Click image for expanded view)

What you're seeing in the top-left corner of that graphic is a real-time radar image showing the strength of the radar returns. On the top-right corner is doppler velocity (that is the whole purpose of a doppler radar versus a standard one - if you want to know more email me at a_shaffer@kdlt.com and I'll explain). On the bottom left is storm-relative doppler velocity, and on the bottom right is computed rotation using an algorithm.

Notice the curve of the storm toward the bottom of the picture - or toward the South. Look at how that is in the same spot as the more whitish colors on the top right. Those are your wind speeds without anything done to them - and they show some areas of high winds with areas of lower winds... meaning rotation. Then... you get to the bottom left image showing bright reds and bright greens side by side. That means winds are moving away from the radar and toward it in close proximity - again showing signs of rotation. All of that is verified by the algorithm showing a bright red bullseye on the bottom left image. All of that being considered - it is no wonder a tornado warning was issued for that storm.

As the system moved farther toward the East, we did get some reports of what now turns out to be just a funnel cloud - with no confirmed touchdown. That could change if someone reports damage or debris, but this is what the storm looked like toward the end of our 6pm show:

(Click image for expanded view)

There was still a tornado warning in place at that time, but if you compare the storm at that point with the previous image, you can see things aren't as boldly tornadic as they were earlier in the storm. That was at 6:20pm, so we still had those reports coming in of a funnel cloud with the rotation, but 11 minutes later the warning was cancelled.

Luckily that was it for any strong storms at that time and presumably for the night. Let me know if you have any questions about anything, as now with this storm over I have some time to answer them.

Take care & have a great night!

~KDLT Meteorologist Aaron Shaffer

Update in progress...