Flood — Marshall, Iowa

2019-03-14 to 2019-03-16 · near St Anthony, Marshall, Iowa

Event narrative

Iowa DOT reported Iowa 14 closed between US 30 and County Road E27. Other secondary roads across the county were also reported closed due to flooding. Many roads and some bridges were damaged from the flooding. The bridge on 140th St. was a total loss.

Wider weather episode

Reports from the 13h through the 19th in this entry.

A relatively deep and widespread snowpack existed across the region during early to mid March. Many areas in central and northern Iowa had around a foot to two feet of snow on the ground, along with many areas in upstream river basins in Minnesota and the Dakotas having similar or deeper snowpacks on the ground. Additionally, with the below normal temperatures throughout the majority of the 2019 year to date, soils were frozen to depths of a foot or more throughout the aforementioned areas. All of that primed the area for potential moderate to major flooding issues should a rapid snowmelt and/or rainfall event occur, which unfortunately came to fruition.

The primary driver was two-fold with warm air advection on the backside of a departing high pressure on the 12th, and a sizable low pressure system that moved through the region on the 13th and 14th. The event began with widespread temperatures and dew points in the upper 30s to low 40s on the 12th with the initial warm air advection, which continued through the overnight hours into the 13th. As the low pressure system developed off the Colorado Rockies, warm air advection continued to push temperatures and dew points up into the upper 40s and low 50s on the 13th and 14th, aiding the rapid snow melt. On top of the rapid snowmelt, which often went from 12 or more inches on the ground to zero in a matter of about two days, light to moderate rainfall occurred ahead of and on the backside of the low pressure system on the 13th and 14th. All combined to cause widespread overland flooding, river flooding, and ice jam issues.

View location on OpenStreetMap → (42.1781, -93.2033)

Source: NOAA Storm Events Database, event_id 813095. Narrative written by the NWS forecast office that issued the report.