When assessing the accuracy of severe weather warning systems, there is only one truth; the ground truth. That is, having people out there actually witnessing the conditions that exist in real time, then reporting that to the weather service.
How many times have you heard there was a severe weather alert for your area that never seems to come to pass? This happens quite often so the accuracy of the warnings are essential to prevent apathy in the public. Every time I am out spotting severe weather, I get the same responses from many in the public, "They put out warnings all the time, but nothing ever happens."
The reason for this apathy in the public is simple. Sometimes the severe reports are inaccurate. Many times, warnings are based solely on a radar observation by someone in an office hundreds of miles away. What is absent from the knowledge of the radar observer is the ground truth. He has no way of knowing for sure if what he is seeing on radar is actually producing severe weather.
Severe weather events can also be very local in nature. Up until the last year or so, severe thunderstorm or tornado warnings were given to a whole county which could cover many square miles, while the actual event is occurring in only a couple square miles of that area. For most people of the county, the severe weather warning seemed to be erroneous, thus leading to an apathetic response to future alerts.
The weather service is now trying to get more accurate with its warning systems and putting out warnings only for those in the actual path of severe weather. There still is that issue of the ground truth as to whether or not severe weather is actually occurring based on the radar observations.
The weather service has become much better in analyzing what they see on radar thanks to an organization called SKYWARN, which is an organized group of storm spotters that, by ham radio, report ground observations of the weather as it occurs to help put out more timely and accurate warnings. What they do is take the ground reports and compare that to what the radar shows so that they can better recognize the difference between what might be severe and what might not be severe.
The accuracy of severe weather warnings are also studied by assessing the damage left behind. The weather service will get reports from local law enforcement, and by trained spotters of the damage left behind and study the location of the damage as compared to what was observed on the radar about the time the damage occurred. This also helps to increase the accuracy of severe weather alerts.
To keep the public as safe as possible, it is extremely important for the severe weather alerts to be as accurate as possible. While the warning system is far from perfect, it is a far cry better than it used to be only 20 years ago and continues to get more accurate with each passing year.