Verified 131 mph Straight‑Line Winds Strike Northern Plains as Severe Watches Continue

Overview

• A sequence of discrete supercells that formed June 27–29 organized into bowing clusters and mesoscale convective systems and produced verified extreme straight‑line winds including measured gusts up to 131 mph in South Dakota.
• SPC issued repeated mesoscale discussions and multiple active severe thunderstorm and tornado watches to coordinate rapid watch issuance with local NWS offices as convective mode shifted from hail to wind threats.
• Forecasters pointed to key drivers — an elevated mixed layer, very moist boundary layers with dewpoints in the 60s–70s, high MLCAPE, and a strengthening low‑level jet — that supported both very large hail and later widespread damaging winds.
• A long‑lived MCS moved northeast into the Upper Midwest and produced damaging gusts such as a measured 68 mph at Spencer, Iowa, with SPC products noting a conditional threat for a few strong tornadoes where low‑level shear was enhanced.
• Local National Weather Service offices and river forecast centers are monitoring for further watch extensions and localized high‑impact wind and hail events as organized systems continue pushing northeast and as post‑event assessments determine whether damage was tornadic or straight‑line.