Friday, May 17, 2013

Updated Weekend Tornado and Severe Thunderstorm Outlook

For Saturday

These are big numbers from northern Oklahoma to eastern South Dakota. I'm very concerned that violent tornadoes and hailstones baseball size and even larger may occur in the hatched area. There is also a possibility of damaging thunderstorms straight-line winds.

For Sunday

For three days out, these are very high numbers. Again, violent tornadoes, very large hail and damaging thunderstorm winds are all possible in these areas, especially the hatching.

This is a weekend to keep up on the weather, especially with a lot of graduation ceremonies and weddings taking place. 


  1. Mike, is it true that these tornado maps can't go up to 100%? Is 60% the highest it can go? (Seems like I remember someone telling me that) And why is that?

  2. It is true, Shawn. The highest probability that can be displayed is 60% and even that is rare. The probability refers to the likelihood of the event within 25 mi. of a given point. The reason the numbers cannot go higher than 60% is due to the filtering system they use.

    Take a look at this blog post from April, 2012, comparing the actual forecast to a theoretical perfect forecast:

  3. Shaun, as I understand it the probabilities are based on the likelihood of severe weather happening within 25 miles of any point in the outlined area. To say severe weather is 100% likely for all those points is impossible, and wrong.

    But for anyone in the hatched area to say "I have a 45% chance of having a severe storm within 25 miles of me tomorrow, and if it happens I can expect large hail and strong tornadoes" would be accurate.

    As I understand it.


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