Monday, June 25, 2012

Shakopee’s freak wind storm

A wind storm blew through Shakopee last Wednesday between 9:30 am and 10:00 am.  This storm toppled a tree at the Donahue residence on Jade Circle, but neighboring trees were unharmed, other than a fallen branch.  So what caused this tree to fall?  Was it straight-line winds, tornado, or something else?  This blog post will attempt to answer that question.

 Photo submitted to the Shakopee Valley News

During the morning hours of the 20th, a thunderstorm complex moved from west to east across Minnesota.  As it approached the Twin Cities, it began to die out, with strong to severe thunderstorms ongoing north of the Twin Cities.  An outflow boundary, or gust front, was created with the southern flank of the boundary moving through the Shakopee area just before 9:40 am.


The sudden burst of winds, combined with a saturated ground from recent rainfall, was likely the culprit for the tree damage at the Donahue residence. 

An automated weather station located near Jade Circle recorded observations approximately every ten minutes.  Checking the history for June 20, 2012 at Weather Underground, it revealed wind gusts to 16 mph at 9:34 and 9:44 am.  It is entirely possible that winds were higher between observation intervals.  Flying Cloud Airport in Eden Prairie recorded a 27.6 mph wind gust at 9:53 am, therefore winds to 30 mph were not out of the question.  Since the tree did not snap, nor were roots exposed, it is reasonable to believe that winds did not reach severe levels of 58 mph or greater.


The south metro had been inundated with rain and wet soils as June 20 approached.  National Weather Service imagery shows 30-day precipitation amounts as of noon on Monday, June 18th in the eight to ten inch range for rainfall.  With the ground this saturated, it would not take much wind force to knock down trees.


it is of this weather enthusiast’s opinion that the felled tree was the result of a sudden burst of wind to 30 mph, with water-logged soil that could not longer support the tree.


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