Monday, June 16, 2014

Updated Severe Weather Discussion for Thursday, June 19

This is an updated severe weather discussion for Thursday, June 19.

CIPS/SLU
This discussion will utilize only analog guidance, as there are some things that need to be clarified with the method as a whole (those caveats will be discussed as we move along). The image above shows tornado, damaging wind and hail reports from the top 15 dates whose conditions match up the best with those forecasted on Thursday. When atmospheric conditions similar to those on Thursday set up, the result is typically a severe weather event in the Midwest, as the image above shows. The hardest hit areas include Minnesota, Iowa, Wisconsin, Illinois, Indiana and Missouri. Phrased better, these states should be prepared to be affected by potentially significant weather conditions this Thursday if analog guidance verifies.

CIPS/SLU
If we look at a probability map from the top eight most severe analog dates, we see that the analog guidance suggests that there may be a 60% or greater chance of severe weather in Illinois, Wisconsin, Iowa, and extreme southeast Minnesota. These percentages are definitely threatening, although considering most recent model guidance, these percentages may actually be too high, not only due to recent developments, but the natural tendency of the CIPS system to seemingly overestimate these events.

CIPS/SLU
Use caution when utilizing this graph. This image shows the percentage of the top 15 analog dates that had a long-track tornado occur, where a long-tracked tornado is defined as a track over 30 kilometers. As you can see, this risk is anomalously high over north central Iowa, where nearly half of the chosen analogs had long tracked tornadoes occur. This may all seem frightening, but the caveats we discussed with the last image stand here as well- I don't think things will be this bad.

The threat for severe weather on Thursday will be examined in the next discussion.

Andrew

Updated Severe Weather Discussion for Wednesday, June 18

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

SPC
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.

CIPS/SLU
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.

CIPS/SLU
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.

Andrew