Saturday, April 30, 2011

May 8-9 Potential Midwest/Great Lakes Severe Storm System (Issued April 30)

There is concern building for a potentially significant severe weather event May 8-9.
 We will see a strong low pressure system drop from Canada into the Upper Midwest. The low will bring with it a supply of cold air. This image is for the period May 8th at 7pm CDT.
The above image is forecast for 1 am, May 9. By then, the low pressure will have quickly moved into Michigan. This does not display what is forecast for temperature differences, though.
The image above is still 1 am CDT May 9th, but it displays projected temperature differences 5,000 feet above the ground. As you can see, a rush of cooler air will be following the low, suggesting some form of cold front or force moving the air into the region.
More concerning, though is the temperature differences. It is projected to be a 10 degree temperature difference, which could turn out to be a 15 degree difference on the ground. That is a pretty substantial difference. With such a strong low and big temperature differences, there is definitely concern for tornadoes.
The image above is the Best Lifted Index. The lower numbers, the more unstable. As you can see, here is a noticeable area of instability in Nebraska, with a number of -8. The image above is actually in the time frame of May 8th at 1 am. That displays an able set-up going into the event.

Lastly, also at 1 am May 8th, is the image depicting a cap. A cap suppresses storms, the more negative the stronger the cap. As we can see on this image, the cap is as low as the legend can go, which is -500 to -900. That is an extremely strong cap. It is very worrying, combined with such instability, strong low pressure.

These two images are the jet stream. The jet stream was up to 150 mph on the April 27 tornado outbreak down south. The first image is May 9th at 1 am, while the second is May 9th at 7 am.
We see the jet stream will be fairly strong, at it reaches up to 100 mph in the Ohio Valley.
Finally, above, is the lower level jet stream forecast at May 9th at 1 am. The lower level jet stream will not be terribly strong, meaning the tornado threat should not be as strong as it was on April 27.
In conclusion, there is a threat for a tornado outbreak and severe weather, but it would not be nearly as strong as April 27.

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