Severe thunderstorm and tornado watches are quite common. Every spring and summer, thunderstorms can become strong to severe. When storms produce hail at least one-inch or greater and/or contain strong winds 58 mph hour or higher, a severe thunderstorm watch is issued. If we add a tornado probability to the wind and hail concerns, a tornado watch is issued. The watch means conditions are favorable for severe thunderstorms or tornadoes in and close to the watch area.
There are times, and it is rare, when severe weather can be significant, posing a greater threat to life and property. That’s when the Storm Prediction Center will enhance the wording in a weather watch and include “Particularly Dangerous Situation”.
PDS tornado watches are put into effect when the forecaster has high confidence that multiple strong tornadoes will occur in the watch area. PDS severe thunderstorm watches likely mean there is a threat of a high end derecho with widespread wind damage.
Just how unusual is the PDS watch? According to the Cooperative Institute for Meteorological Studies at the University of Oklahoma, of 3058 tornado watches issued from 1996-2005, just 7% were labeled “PDS”. Most of the 216 “particularly dangerous situation” tornado watches covered the lower Mississippi Valley with the Plains states coming in second.
The study says the motivation for using the PDS wording is to communicate to the public the significance of the severe weather threat. EF2-EF5 tornadoes represent less than 10% of all tornado reports, yet they produce over 90% of the fatalities and 80% of the injuries and damage.