Monday, June 16, 2014

Updated Severe Weather Discussion for Wednesday, June 18

This is the latest severe weather discussion for Wednesday, June 18

The Storm Prediction Center has outlined a large Slight Risk of severe weather for the North Plains all the way into the Northeast region. States affected include North Dakota, South Dakota, Nebraska, Kansas, Minnesota, Iowa, Wisconsin, Illinois, Michigan, Indiana, Ohio, Pennsylvania, and New York. The Plains states that look to be affected by this event are included in a hatched outlook, indicating that the risk of significant severe weather (i.e. strong tornadoes, extremely large hail, and extreme damaging winds) is elevated in those regions.

We can also use analog dates to predict the future. This method of forecasting takes decades of weather observations and matches a handful of select dates up that are closest to the forecasted conditions. This image shows compiled severe weather reports from the top 15 analog dates, basically the 15 days that were the closest to projected conditions on Wednesday evening. When we do take a look at these compiled storm reports, the prognosis for Wednesday is shocking. We see an epidemic of significant storm reports over the northern Plains, including significant and long tracked tornadoes. Conditions similar to the ones expected Wednesday resulted in an outbreak of severe weather primarily over southern Minnesota, western Iowa, much of the Dakotas, and eastern Nebraska.

The graphic above shows a mean probability of severe weather being reported in any given area, based on the top eight analogs. As the image shows, probabilities exceed 60% in northeast Nebraska, southeast South Dakota, Minnesota, and northwest Iowa. A still-threatening 45% risk extends across a large chunk of the north Plains, but it is that 60% risk area that has me worried. Right now, the SPC is retaining a Slight Risk for this area with the significant risk hatching, and I feel like that is the right move. While I'm nowhere near the level of expertise of an SPC forecaster, retaining a Slight Risk into the event, with the chance (NOT a guarantee) of an upgrade to a Moderate Risk on the table for Wednesday would be what I were to do if I were an SPC forecaster. For right now, though, this event does look to produce severe weather across the northern Plains. The question is, how severe will things get? That question will be answered in tomorrow's discussion.


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