Concealed in darkness and invisible to the naked eye, the tornado is a ghost among the night. It belongs to the wind, a catastrophic wrinkle in the air that constantly surrounds us. We can’t see it but know it’s there and the only physical sign of its presence is a shocking trail of buildings damaged and lives destroyed.
Is this the true character of Wisconsin tornadoes? Not exactly, but it was the character of tornadoes during the 2014 season. With Wisconsin severe weather season over we will take an early look at the numbers and make some comparisons to other seasons.
NEW STANDARD FOR EVENING TORNADOES
Darkness was kind for Wisconsin tornadoes this summer where 16 tornadoes occurred between 10PM and 8AM. In years with more than five tornadoes recorded since 1950, 2014 ranked second in total number of evening tornadoes behind 1980(18,40%) and first in percentage of evening tornadoes with 72%(16 of 22). This means nearly three out of every four tornadoes occurred during the evening or early morning hours! The morning slow hours of 5-7AM saw one tornado this season and the first during that time since 2010.
SLOWEST SEVERE SEASON SINCE 2009
A total of 340 severe weather reports have been filed thus far in 2014, an impressive 240(40%) below the 20 year average. If it ended today, 2014 would be the slowest year for severe weather since 2009(281) and third slowest in the last 20 years. With respect to all three severe weather report types of the last 30 years, tornado and wind reports in 2014 were slightly elevated while hail reports were down. It was a down year for hail with only 17 hail reports prior to July and a total of 122 to finish out the season.
The first tornado of 2014 arrived on the evening of June 16 making it the seventh latest start since 1950. Of the top seven latest starting years, 2014 had the most tornadoes.
THIRD SHORTEST TORNADO SEASON
Compared with years that have more than five tornadoes, the time between the first and last tornadoes of the 2014 season was the third shortest since reliable records began in 1950. It was shorter than the year 1983 by only four hours. It is also interesting that the first and last tornado dates were are almost identical to 1983.
Tornadoes arrived in bunches in June when 18 of the 22 twisters occurred. Of those 18 tornadoes, 15 arrived during the late evening and early morning hours in outbreak fashion. 11 occurred on the evening of June 16/17 and four on June 29. The remaining tornadoes were sprinkled across June, July and August.
COMPARING TORNADO INTENSITY
Most similar year in regards to tornado intensity was 1992. June saw the first EF3 tornado since 2011 and one of only two F/EF3 tornadoes to have occurred at night. It was the longest tracked evening EF3 tornado on record at 1mi. The other evening EF3 occurring in 1967 in Dane county killing two people and had path width of 200 yards and length of 0.1 mile.
WHAT WE HAVE LEARNED
The evening peak in tornado frequency is more than statistical magic, it is (we think) the signature of convective complex type tornadoes. It represents almost an entirely different process of tornado formation that is both hard to document, research, and predict. Convective complex type tornadoes tend to be weaker EF0-EF1 but on rare occasions stronger EF2-EF3 tornadoes can occur.
We observed in 2014 the surface warm front playing a key role in such situations. A warm front was present on both June 16 and June 29 interacting with the apex of bowing thunderstorm complexes. Exactly how the warm fronts interact with thunderstorm complexes such as bow echoes and bookend vortex(BEV’s) remains poorly understood and incredibly critical.
We also need to do a better job of anticipating how thunderstorms change the atmosphere. We tend to judge severe weather potential on regional parameters. Many Wisconsin tornadoes are indirect responses to modifications caused by ordinary thunderstorm evolution even if regional parameters are un-supportive of them. If we do these things better we can cut down on the number of unexpected tornadoes Wisconsin experiences each year.
Our lives may take us in different directions but we all expect to be back chasing Wisconsin storms next season. The draw of the unknown and beauty of nature keeps us coming back. We hope that our recent contributions to the scientific knowledge base on this topic helps others more accurately predict future severe weather events. We also hope that the recent trend towards dangerous night time tornadoes ends with this season.
OTHER 2014 TORNADO FACTS
*WIDEST - Clarno, WI EF1 that occurred on June 17 at 4:40 AM. It was 641 yards (1923ft) wide with a path length of 6.75 miles. Second widest was the June 29 Fennimore EF1 at 600 yards.
*LONGEST(mi) – June 29 Dodgeville EF1 tornado at 29.7 miles. It was the ninth longest tracked EF1 tornado since 1950. Tornadoes logged 76 miles across Wisconsin this season.
*COSTLIEST – Verona EF3 at 15 million dollars of property damage. Tornadoes caused 37.1 million dollars in damage this season