Thunderstorm Wind — Bremer, Iowa

2019-07-20 · near Waverly, Bremer, Iowa

Event narrative

Numerous tents on the fairgrounds were blown down with people in them causing some injuries. In another place in town a woman had a broken arm when a tree fell on her while mowing the lawn. Several trees fell across the area with some additional injuries. There was no thunderstorm in the area, as they were to the north, but the strong gust front from the storms up north produced the damage.

Wider weather episode

The atmosphere was juiced so to speak ahead of a cold front sliding into the region. MUCAPE values very quickly approached and exceeded 4000 J/kg by mid-morning. With the cold front and previous storm outflows the impetus for new convection, discrete storms were not expected, with the prevailing storm type being the linear or quasi-linear convective system (QLCS) variety. Additional support for the QLCS mode was seen with, once again the cold frontal and outflow forcing, highly unstable atmosphere, and little to no convective inhibition. Additional support for strong winds was seen with DCAPE values in excess of 1500 J/kg across much of the area Once a system began to produce a decent cold pool, there would be little to prevent it from progressing.

That was evident in Iowa as two distinct QLCSs moved through. First in the morning hours across northern Iowa, and second during the late morning through evening hours from central Iowa and on toward south central and southeast Iowa. In both cases, damaging winds widely prevailed. Across northern Iowa the gust front roared out ahead of the line of convection, continuing to produce severe wind reports in areas of no storms well to the south and east. In central and southeast Iowa, widespread reports of 60 to 70 mph winds and various tree damage (from large limbs to entire trees) were received along a path from roughly Perry, IA through Ottumwa, IA.

View location on OpenStreetMap → (42.7203, -92.4799)

Source: NOAA Storm Events Database, event_id 846754. Narrative written by the NWS forecast office that issued the report.