Tornado season deadly this year
Mention severe weather and most people think about severe thunderstorms – with their gusty winds and hail – or tornadoes. This has been a deadly and destructive year for tornadoes, with nearly 1,200 storms resulting in 110 fatalities reported so far.
The death toll makes this the deadliest tornado season since 1998, and there are still several months left in the prime tornado season. Parkersburg, New Hartford and Dunkerton in northeast Iowa were the latest communities to suffer the costly effects of a killer tornado. On May 25, a strong tornado packing winds of up to 205 mph carved a damage path of 43 miles and up to 1.2 miles wide through the state.
In addition to destroying numerous structures in its path, the storm caused approximately 70 injuries and six fatalities. After a damage survey, the tornado was given the highest ranking of EF-5 on the enhanced Fujita damage scale, the only EF-5 to occur in Iowa since June of 1976.
Fortunately, the most destructive tornadoes do not form undetected by National Weather Service meteorologists. These killer tornadoes come from thunderstorms called “supercells,” which are thunderstorms exhibiting rotation. This rotation can be picked up by the wind velocity display on Doppler radar. In the precipitation display, which is what most folks see on TV, many tornadoes will also produce a signature called a “hook echo.” The intense circulation of the tornado causes the rain to wrap around it, resulting in a hook-shaped image on the radar screen.
Numerous storm spotters and/or chasers across the Midwest also serve as extended “eyes” for the National Weather Service, calling in reports of tornadoes as they witness them. A tornado warning will be issued by the NWS when a tornado is either indicated on radar, or reported by a spotter. The warnings usually cover specific counties for a set period of time. Tornado watches, on the other hand, are issued by the Storm Prediction Center in Norman, Okla. The watches are issued for larger geographic areas which can cover one or more states, and only indicate the potential for tornado producing storms during the period of the watch.
The average lead time for tornado warnings is 13 minutes. A warning won’t be worth anything, however, if it doesn’t get to the public. Some communities in tornado-prone regions use sirens, which wail when a warning has been issued. Warnings are also disseminated through the emergency alert system, through local TV and radio stations newscasts, and on weather radios. Even in an area such as this, where the occurrence of severe storms is low, it is a good idea to always have a working battery-powered radio or weather radio on hand.
My husband, a lead forecaster at the Spokane NWS, and I have lived in this area for nearly nine years. He recalls only a handful of instances where tornado warnings were issued for Eastern Washington or North Idaho. Severe thunderstorms containing large hail are also uncommon. The area does see its share, however, of damaging winds – either within or ahead of a thunderstorm. These winds are enough to result in power outages, downed fences and/or uprooted trees.
The first severe thunderstorm of the season moved through Latah County last Wednesday and did produce nickel- to quarter-sized hail between Deary and Harvard. The threat for severe thunderstorms continues in the area through June, before hot and dry summer weather usually sets in.