October 14, 1966 a late season tornado outbreak in Iowa included a killer F5 twister that struck the town of Belmond. With winds of at least 200 mph, this is the only known October EF to have ever occurred in the United States.
A strong surface low, very steep mid level lapse rates, and moderate directional wind shear combined to produce at least twelve tornadoes across Iowa.
Having extreme instability present over Iowa at this time of year does happen occasionally. As the surface low moved into Western Iowa a warm front lifted to the north as dew points near 70 surged in. Surface winds in northern Iowa backed nicely as breaks in cloud cover pushed temperatures into the upper 70's and low 80's. Thunderstorms developed in the early afternoon and raced to the NE.
The storm that produced the F5 tornado developed just NE of the triple point where backed surface winds were optimal.
The tornado struck Belmond at 2:55 PM just minutes after the home coming parade ended. Damage was extensive throughout town, 6 people died and over 170 were injured.
Many farms suffered damage along the tornado's path, at least three were completely leveled.
As the surface low wrapped up and moved to the NE, Sioux City Iowa just to the west received four inches of wet snow.
As an 11 year kid I remember being fascinated that such a powerful storm could produce such a violent tornado and snow within 100 miles of one another. I cut out articles on the tornado from the Des Moines Register, Cedar Rapids Gazette, and Iowa City Press Citizen and put them in a scrap book. I still have it today. This remains one of the most unusual storms in Iowa weather history and there have been plenty. If you have any thoughts or remember this unique event please chime in on the forum.
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