Testing a New Severe Storm Index
By Quincy Vagell on July 22, 2012, 11:55pm
Use your ← → (arrow) keys to browse more stories.
1 of 2 
I've been toying with some variables to come up with a severe storm index...
The whole idea here is to take into account several variables and then come up with some sort of risk assessment based on those numbers.
For some background information, my proposed index uses 10 variables:
- CAPE (potential energy)
- Lifted Index
- Low-Level Lapse Rate
- Effective Bulk Shear
- Storm Relative Helicity (effective)
- Supercell Composite Parameter
- Significant Hail Parameter
- Derecho Composite
- Craven Significant Severe Parameter
- Trigger Mechanism (ex. cold front)
I broke down the variables into different categories. For example, if CAPE is forecast to be low, it will get a lower number. If CAPE is high, then the resultant number is high, meaning that the potential for severe weather increases.
The idea here is that one variable alone cannot forecast severe weather perfectly. Everything must be considered.
The values for each variable are added up and the sum is divided by 10. So, if one of the 10 variables is not available or it's missing, just divide the total by 9.
What do the threat values mean?
- 0: No Storm Threat. There is zero severe storm threat.
- 1: Isolated Slight Risk. There is a slight risk of an isolated severe storm.
- 2: Low Risk. There is a low risk for severe thunderstorms.
- 3: Moderate Risk. Severe weather is expected, but not all areas will see it.
- 4: High Risk. Severe weather is likely and many areas will see it.
- 5: Extreme Risk. Severe weather is likely and the storms could be extremely dangerous.
Testing the index:
- I ran a couple of dummy tests to make sure the index checked out and I believe it does. For this past Wednesday, it yielded a value of 3.4 for NW CT. There were at least three confirmed severe thunderstorm reports here. Severe weather was expected, it did happen, but not all areas saw it.
- For Sunday, the value was very close to zero. This makes sense, since there was no convective activity and absolutely no severe thunderstorms.
I plan on testing this index out in the near-feature to see how it performs.
Based on what I've already seen, I think this index could be very valuable. There are times where the SPC may issue a Severe Thunderstorm Watch, but many of the signs point towards little to no risk of severe weather. It will be interesting to see how it pans out.
As is the case with any research project, there will need to be tests done to check for verification. Trial and error is key!
For information on how I rated each variable, advance to the next slide.
