Thunderstorm Wind — Polk, Iowa

2014-06-17 · near Des Moines, Polk, Iowa

Event narrative

Thunderstorm winds blew down a large tree branch. A homeless individual died when a the branch fell on him at a homeless settlement along the banks of the Raccoon River east of Fluer Blvd.

Wider weather episode

A very dynamic weather pattern was in place over over Iowa. A warm front lifted north into the state. Temperatures warmed in the 80s with dew point readings in the upper 60s to mid 70s. The atmosphere became very unstable with 3000 to 4000 J/kg of CAPE and downdraft CAPE of 1000 to 1500 J/kg. The shear was strong with 50 to 60 kts available. The freezing level was quite high, between 13,000 and 14,000 feet wtih CAPE in the -10 to -30 C layer of the atmosphere between 700 and 900 J/kg. The precipitable water value was a between 1.5 and 1.8 inches. The LCL was relatively low, around 1000 meters. Thunderstorms moved into western Iowa out of Nebraska. As the afternoon and evening progressed, the thunderstorm complex evolved into one that was more outflow dominated. The system raced southeast and produced high winds across the Des Moines metro area and to the east and south. Winds of 60 to 80 MPH caused considerable tree and power line damage. Power outages were reported by 27,000 customers in Des Moines at the height of the storm. As the storms moved through the heart of Des Moines, a homeless individual died when a large tree branch fell on him at a homeless settlement along the banks of the Raccoon River east of Fluer Blvd.

View location on OpenStreetMap → (41.5779, -93.6418)

Source: NOAA Storm Events Database, event_id 513992. Narrative written by the NWS forecast office that issued the report.