June Tornadoes - How Did We Do?

Back on June 1st I wrote about the fact that the 2010 tornado season across Nebraska had been relatively quiet with only 11 tornado reports through the end of may compared to the average of 17. I also discussed what the probabilities were that June (the peak tornado month in Nebraska), as well as the remainder of the tornado season, would continue the quiet streak based on what activity had been in the months March through May. Please see the graphic below:



















As you can see from the graphic, when the March-May period has fewer tornadoes compared to the averages, chances are that June and the year as a whole will be below average. However, when the March-May period has an above average number of tornadoes, June has a 50-50 chance of being above or below average, while the chance that the year will be above average is quite high at 86%!

So how did we do during the month of June tornado-wise across Nebraska? Well, first of all, I need to explain how the Storm Prediction Center (SPC) reports the tornado counts.

The count begins with what is know as "Preliminary" tallies, where all tornado reports are counted. These preliminary counts may remain for several months and be revised up or down before SPC issues what they call the "Actual" count. For example, in my graphic above, the number shown for the March-May period is 11. However, SPC revised the March-May count for Nebraska up 2 in their Preliminary tally to 13, still below the average of 17 but up from the original preliminary tally.

So now we have 13 tornadoes for the March-May period. For June, the SPC Preliminary count for Nebraska was 25, well above the average of 15 as shown in the graphic. However, what will the "Actual" count be when SPS releases it later this year? Typically, the Actual counts are lower, and sometimes much lower because the Actual counts are released after NWS employees confirm whether a tornado occurred based on what they find at the site at which the tornado was reported. Sometimes they find that a tornado did not occur - perhaps straight line winds caused damage that was mistaken for a tornado. Or perhaps what was seen was a gustnado - these look like tornadoes but are not formed in the same way as actual tornadoes, and are weaker versions of tornadoes. Or perhaps a tornado was counted multiple times, so two or three reports may have been of the same tornado rather than different tornadoes in the same area.

However, the Actual count would need to be revised significantly downward by at least 10 in order to have a count for June that is not above the average of 15, and I don't think that will occur. So in the end I believe that June was an above average month for tornadoes in Nebraska, and this means that June went against the statistical probabilities as shown in the graphic.

So what will the final count for the year be? Well we will need to wait for that for at least a few months, but unless July and August are well above average, it will probably end up somewhere relatively close to average though a bit above. I'll have the final figures a bit later when they are released.

Mike