We talk often in the spring and summer months about the certain risk levels that the Storm Prediction Center in Norman, OK issues. These risk levels come from what the SPC calls Convective Outlooks, and we use these together with forecasting techniques that we know to help predict severe weather in our area.
These outlooks are issued at 2 AM, 9 AM, 12:30 PM, 4 PM, and 9 PM. But is change on the way for how these risk levels are communicated? After doing some research, change may not be such a bad thing. The current risk levels being used are: General Thunderstorm, Slight, Moderate, and High.
I decided it was time to look at the Day 1 Outlook issued at 12:30 PM each day from March 20 (start of spring) until today, and see how many storm reports fall within each risk area. Let me clear right off the bat. I understand that there are some biases in this because:
1) Each risk area is of a different size, with General being larger than Slight and Slight being larger than Moderate. Therefore, the amount of storm reports may be skewed in a certain direction. Still, I think the results are worth showing. 2) The results may depend on location and what the day's weather set up is. Basically what I'm trying to say is that I understand that every day is different, and brings with it different dynamics. 3) The numbers I have come up with are roughly approximations, however, they give off the basic gist of what I'm trying to convey in this blog.
Damage reports are filtered into the SPC website for tornadoes, hail and wind. For each General, Slight and Moderate risk area that shows up in a 12:30 outlook, I wanted to see how many tornado, hail and wind reports show up within each risk area during a day.
On the average, here is how the numbers play out:
If a Slight Risk averages out to hold 47 wind reports, five tornado reports, and 37 hail reports from March 20th – June 29th, 2014, then why are we referring to the risk as Slight? Well, the Storm Prediction Center is already working on that. The proposed plan has been to replace the General Thunderstorm outlook with the phrase ‘Marginal' and replacing the upper end of the Slight Risk with the phrase ‘Enhanced.'
Here's my two cents. Take out the word ‘slight.' Just can it. When we forecast a slight chance of rain, it is interpreted that it likely won't rain. But then when the SPC forecast a Slight Risk of severe weather, we're talking about a good chance of seeing high winds, hail and possibly an isolated tornado. That doesn't line up.
What if this is just a verbal adjustment and not one based on statistical probabilities? What if all we have to do is use Marginal in place of General Thunderstorm and Enhanced in place of Slight?
While this proposed change is still said to be in the public comments stage, I want to know what you think. What words do you think help convey a severe weather threat? Send your comments to any of the sites below.
---Meteorologist Chris Michaels---
Facebook: Chris Michaels WCYB