National Weather Service United States Department of Commerce

Tracking Late December Winter Storm Expected to Impact the Northern Plains through the Northeast U.S.

A winter storm system will rapidly intensify over the Midwest on Sunday and track through the Great Lakes on Monday. Periods of heavy snow are anticipated across the Upper Great Lakes late Sunday and continuing into Monday. At least 1/10 inch of ice accumulation is expected from a wintry mix across much of the interior Northeast U.S. starting Sunday afternoon. Read More >

Overview

From the evening of May 20th through mid afternoon on May 21st, several waves of thunderstorms produced tornadoes, damaging winds with gusts up to 90 mph, hail up to tennis-ball size, and extremely heavy rainfall, which resulted in considerable flash flooding and river flooding.

Six tornadoes (5 EF0 and 1 EF1) occurred with a fast-moving line of thunderstorms that moved through eastern Nebraska and southwest Iowa during the early morning hours on the 21st. An additional 4 tornadoes occurred with a second round of thunderstorms (supercells) that formed over far eastern Nebraska and tracked through southwest Iowa during the late morning and early afternoon hours on the 21st. 

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Radar loop from 4 PM on May 20th through 3 PM on May 21st
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