The 2013 Iowa severe weather season started out as 2012 had ended, on a quiet note. With unseasonably cold air trapped across the region, news headlines were instead dominated by our extended winter and late season snowstorms well into early May. There were a smattering of severe hailstorms from late March through the first half of May, but no tornadoes during these first two months of Iowa’s climatological “tornado season.” This tornado drought, coupled with the earliest end to Iowa’s tornado season on record in 2012 (May 24), enabled Iowa set a record for the most consecutive days between tornadoes on May 15. The old record was 355 days set between May 5, 1955 and April 26, 1956. Iowa almost made it a full year without tornadoes, but a severe weather outbreak on May 19 solidified the 2012-2013 record at 359 days.
On May 19 a supercell thunderstorm over southwestern Iowa morphed into a squall line to the southwest of Des Moines and produced three brief tornadoes along its leading edge in Dallas and Story counties (radar image on left). These tornadoes were rated either EF1 or EF0 and impacted several homes and farms along their paths. A line of thunderstorms lifting north across eastern Iowa dropped a pair of EF1 tornadoes south and west of the Davenport area on May 30, damaging the towns of Conesville and Buffalo. The following day a rain shower over northeastern Iowa produced a short-lived landspout tornado in Floyd County. Landspouts (also known as “cold-air funnels”) are a special type of tornado that form under weak storms and rarely touch down or produce any damage.
The next severe weather outbreak took place on June 12 across northern Iowa, with one storm producing five tornadoes over the span of an hour across Wright and Franklin counties. The town of Belmond was grazed by two tornadoes, including a strong EF3 that severely damaged several homes and businesses. The storm that spawned these tornadoes was known as a “cyclic supercell” or a storm capable of generating multiple tornadoes, possibly at the same time. This was the case with the Belmond storm, where two tornadoes were occurring at the same time at several points during its lifecycle.
Two tornadoes were recorded in late June, with an EF1 squall line tornado tracking through northern Muscatine and a brief landspout touchdown taking place in Webster County. High pressure built into the region as July set in, putting an end to the summer tornado season. Should the Iowa tornado season have ended there, the state would have set a record for the shortest tornado season (38 days, May 19 to June 26) and the least number of tornadoes in a calendar year (15). However, this was not to be the case…
On October 4, an unseasonably strong area of low pressure lifted northeastward across Nebraska, spawning eleven tornadoes in northwest Iowa during the late afternoon and early evening hours. This included a pair of strong tornadoes rated EF-2 or higher (radar image on left). Tornadoes were reported in Woodbury, Cherokee, Plymouth, Monona, Buena Vista, and Clay counties. This same weather system also produced an EF4 tornado in northeast Nebraska that struck the city of Wayne, and brought record snowfall and blizzard conditions to western South Dakota.
Overall, Iowa saw 26 tornadoes in 2013, well below the 30 year average of 47 tornadoes. Just under two thirds of Iowa’s tornado activity was concentrated on two days: June 12 and October 4. The four EF2+ tornadoes of the season also occurred on these two days. If you would like to see the full list of tornadoes that occurred this year, the national weather service has them posted here.
“National Weather Service Weather Forecast Office.” 2013 Iowa Tornado Information. N.p., 12 Nov. 2013. Web. 13 Nov. 2013.