By KSN Chief Meteorologist Dave Freeman

Dear Friends and Colleagues at the National Weather Service,

Let me begin by saying that salutation is meant sincerely and truthfully: your Service is filled with dedicated, hard-working, intelligent folk who are committed to protecting lives and property. We are very happy-proud, really-to be your partners in the process of warning our viewers about dangerous weather conditions. This letter is not meant, in any way, as a criticism of your efforts.

The purpose of my letter is to ask for some serious consideration of how we might improve our joint service to the public by revisiting the issue of "what is a severe thunderstorm?"

In asking this question, I would like to frame the discussion not in our world-as meteorologists-but in the world of the folks who are our customers-Bill and Betty Lunchbox. The warnings the National Weather Service issues are, after all, intended to protect these folks from dangerous weather conditions. In the professional weather community, we hope that people pay attention to our warnings, and that they take appropriate action when dangerous weather approaches. The problem is, what we define as a "dangerous" thunderstorm many times isn't really all that dangerous.

Now before anyone has a stroke, let's take just a minute to review the history of how a "severe" thunderstorm came to be "severe." In his excellent article "The Evolution of Severe Thunderstorm Criteria within the Weather Service," published in Weather and Forecasting in 1989, Joseph G. Galway recounts the evolution of the definition of a severe thunderstorm. It turns out that it is at least partially based on something that has absolutely nothing to do with the general public! And, it most certainly has nothing to do with the way that warnings are issued and used today.

The current definition of a severe thunderstorm is: wind of 58mph or more and/or hail at least .75" in diameter (the size of a penny; a dime is NOT .75", it is .71"). Now, from where I sit, the wind criteria is probably in the right ballpark. When wind reaches 60mph or so, it does begin to do minor property damage and so is relevant and important to the general public. Folks would want to secure loose items outdoors, and stay clear of windows in case they would be broken by flying debris.

Unfortunately, this is not the case with penny sized hail. Just by itself, penny sized hail is not going to do any serious damage. It will be loud, of course, but it isn't even enough to dent most cars. It does not require anyone to go to shelter. In short, penny sized hail just by itself is not what most people would define as "dangerous." So where did this .75" idea come from? According to Mr. Galway's article, it comes from the world of 1950s aviation! Three-quarters of an inch was identified in a 1952 report by a government aviation advisory committee as being "the smallest size of hailstones that cause significant damage at airplane speeds between 200 and 300 mph." This was adopted by the National Weather Service as the criteria for a severe thunderstorm in 1954. Last time I checked, my house can't do any more than 5mph. Heck, even my car can't do better than 75...er, uh, 70, on the Kansas Turnpike.

Little did these folks realize that 50 years later thousands of TV viewers would be purple in the face because a weather warning would be crawling across the final moments of "West Wing" to warn about "dangerous" penny sized hail. Little did these folks realize that 50 years later the explosion of technology would enable the public to be notified of these warnings in seconds by TV, radio, pagers, weather radios, and the Internet, at all hours of the day and night.

Friends, let's take another look at this. In fact, let's go back to the future-most of the early attempts at defining severe thunderstorm used hail the size of quarters, 1" in diameter. Hail this size will dent cars, it will even break windows and it most certainly will give you a knot on the head. In other words, it is something that is "dangerous," that folks at home need to know about and need to pay attention to.

Adjusting the criteria to 1" hail would also have another, important benefit. Night after night, folks see warnings on their TV screens for storms that do not require any special action or attention. The effect is they tune those warnings out! Then, when there is a severe thunderstorm with golf ball, or even softball sized hail, they are caught unprepared and folks get hurt. If we increase the severe hail criteria to 1", we will reduce the number of warnings and place the emphasis on those storms that really do have the potential to cause harm.

I know that this issue has received some serious consideration in the last couple of years, but we just can't quite get over the hump. Let's get together as a weather community and get it done. Let's put the warnings out on the storms that really are a threat to public safety and give those "ER," "Friends," and "Law & Order" fans a break on the other nights.

Thanks for your consideration.

Dave Freeman
KSN Chief Meteorologist
weatherlab@ksn.com