Important Changes Coming to SPC Convective Outlooks! Friday Update – 9am #alwx


Good morning! There are some important changes coming to the Storm Prediction Center’s convective outlook this Fall. The SPC will switch to the new system of outlooks on Wednesday, October 22nd, 2014. The old categories included from lowest to highest risk: Slight, Moderate and High Risk. Starting this Fall, the new categories will include from lowest to highest risk: Marginal, Slight, Enhanced, Moderate and High Risk. The image above is an example from April 27, 2011. To the right is how the new convective outlooks will appear, and to the left is how the old convective outlooks appeared. 

In the past, we have struggled with the term, “Slight Risk.” Often in Alabama, a slight risk may include an active severe weather day, with tornadoes, hail and damaging winds, or a slight risk may be issued when we’re expecting one or two storms to produce hail and wind damage. There is a large variation between the low end of a slight risk and the high end of a slight risk, and it is hard for the average person to understand why to take a slight risk very serious on some days and not so much on others. The term “Slight” can be misleading… The new breakdown of the old slight risk should help the average person understand what event to take a little more serious.

The old moderate and high risk will remain the same, as these risks are well understood by the public. A moderate risk indicates the risk of a severe weather outbreak, while a high risk is your major event we talk about for years to come. Understand, if you are under a moderate or high risk, this doesn’t automatically mean we are going to have a tornado outbreak. Each severe weather event is different, and some events have a higher risk of hail or damaging winds and a lower risk of tornadoes. There are some events where the main risk is tornadoes… It’s important to keep a close eye on our forecast when leading up to a severe weather event, so we can clarify what type of severe weather can be expected. 

Below is a break down of the percentages needed to classify the severe risks. The top group is for day 1, which is broken down into a tornado risk, wind risk and hail risk. On the top row of that group shows the percentages needed for the provided risk. The next group down is the day 2 risk, which includes all severe weather and isn’t broken down. Below that is day 3 and below that is Day 4-8…

SPC_2014_Prob vs Cat Outlooks

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Richard Scott

WVUA Chief Meteorologist

Twitter: Richard_wvua



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