Thoughts on changing the warning criteria for severe thunderstorms.
 By Paul Sirvatka

We all know what makes a severe thunderstorm: winds greater than 58 mph and 3/4 inch diameter hail. (tornadoes will be left out of the discussion for obvious reasons.) We also know that the weather service issues warnings based on radar signatures and spotter reports, both of which are prone to a high degree of error. The Storm Prediction Center (SPC) in Norman, Oklahoma issues a severe thunderstorm watch when they expect thunderstorms to form that will meet these criteria. From an emergency management's point of view, marginal severe weather cases cause the same response from spotters as the cases where there is a wide-spread danger of damaging winds and large hail. Spotter activation in marginal cases of severe weather cause a burn-out in spotters and a "cry wolf" syndrome among the general public. I believe that we can best serve public interest by increasing the lower limits of the severe thunderstorm criteria.

The general public tends to ignore severe thunderstorm watches and warnings, at least more so than tornado watches and warnings. Unfortunately this defeats the purposes of issuing such statements. Severe thunderstorms are capable of producing serious threats to life and property. In addition, as is mentioned in many call-to-action statements along with severe thunderstorm warnings, "severe thunderstorms can and occasionally do produce tornadoes with little or no advanced warning". Since severe thunderstorms are dangerous but produce a great deal of apathy among the public, one must seriously why such a reaction occurs.

I believe that part of the reason comes from the loose usage of the term "severe". Often times media uses the word severe to represent any situation where thunderstorms occur and cause some sort of associated problem. Flash flooding, frequent lightning and even the occurrence of enough rain to disrupt traffic can be used to justify the use of the description severe. This is in part due to the media outlets' ignorance of the actual definition of a severe thunderstorm. Nonetheless, it leads to the improper use of severe to describe those thunderstorms that do not pose a significant threat to the general public. It is important that all reserve the use of "severe" to those thunderstorms that pose a serious threat to life and property.

With that in mind, I believe that a thunderstorm producing a 60 mph wind gust and dime-sized hail does not pose a significant risk to the public. Whereas, there may be some risk involved, the risk is minimal and virtually unpredictable. I believe we should increase the minimum wind criterion up to what would be considered minimal F-1 damage on the Fujita scale, or 73 mph. I believe the minimal hail size should be greater than 1 inch hail, (which would be larger than a quarter). Although the minimum size could be larger still, this gives spotters an easy to measure criterion. I believe that this would still give the forecaster a margin of error of at least 10% without significantly increasing the public threat. It is this professional's experience to state that a 60 mph wind and dime-sized hail do not produce a severe weather threat and therefore should not be treated as such. An 80 mph wind and golf ball-sized hail do pose a significant threat and should be treated with utmost urgency.

By increasing these minimal criteria, we may reduce the number of severe weather watches and warnings given in marginally severe cases. This will benefit those who have much to do in providing for public safety. There will be less chance for burn out and an increased active response from the public.

Since the ultimate goal of the watch and warning system is to provide lead time for public response, limiting the events which will seek public response can only serve to underscore the significance of the requests when they are issued. After all, what good is providing a warning if no one heeds them? I believe we should start limiting the calls-to-action and using them only when the situation actually poses a public threat.

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