National Weather Service United States Department of Commerce

Overview

 
Through the day of April 1, a warm front lifted north and left much of the area in a warm, moist, and increasingly unstable airmass. This instability combined with strong vertical wind shear to support multiple waves of severe thunderstorms that tracked along and south of I-70 from the evening of April 1 through the early morning of April 2. Through the evening, thunderstorms took the form of isolated supercells producing large hail up to golf ball size (1.75" diameter) and hen egg size (2" diameter) and isolated damaging winds near the Missouri River into the western and northern St. Louis metropolitan area in addition to a brief EF0 tornado in Chesterfield, MO. Later into the evening and overnight, a gradual transition to clusters and lines of thunderstorms occurred accompanied by hail up to quarter size (1" diameter) and damaging winds. Lastly, these multiple rounds of thunderstorms, some with sustained heavy rain from training, yielded narrow swaths of 2–4" of rainfall which led to some instances of flash flooding primarily in the urbanized St. Louis metropolitan area. Radar loop of entire event
A loop of KLSX radar data from the evening of April 1 through the early morning of April 2.
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