Heavy snow and difficult travel expected again, heaviest snow in southern Minnesota

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Meteorologists may be studying last Friday and Saturday’s severe storm outbreaks for a long time to come. The storm complex blew up over Minnesota Friday afternoon and morphed into a massive 

This highly detailed 1-minute #GOES16 visible satellite loop with SPC Storm Reports overlaid shows the life cycle of Friday’s incredible system. 

NOAA GOES-16 visible satellite loop from Friday July 19.

A second storm complex blew up over South Dakota Saturday, then raced through southern Minnesota into Wisconsin. NOAA is still studying the back-to-back weekend derechoes.

This is why I and other meteorologists were sounding alarm bells Friday. One key measure we look at when assessing severe storm potential is called Convectively Available Potential Energy. (CAPE) A typical summer CAPE value in southern Minnesota might waver around 1,500 j/kg.

Friday’s value of 8,300 j/kg from the NWS balloon launch in Chanhassen is the highest ever recorded. 

The storms caused scattered tree damage and produced hail up to 3 inches in diameter in Minnesota. 

But damage is much more extensive in Wisconsin. Tens of thousands of trees were snapped off or uprooted across northern Wisconsin.

There were a few tornadoes reported over the weekend. 

But most of the the widespread wind damage associated with the weekend storms is called a downburst. These damaging wind events occur along the leading edge of rapidly advancing squall lines called bow echoes. Swirls along either edge of the bow are called bookend vorticies. You can clearly see the bowing signature evolve on Friday’s evening’s radar loop across northern Wisconsin.

Smaller scale downbursts are referred to as microbursts. The scale of last weekends 

 to use the term macroburst. Damage was extensive and widespread.

The damage swath for one of these events was 15 miles wide and 25 miles long, with wind speeds over 100 mph. Here’s the 

event description from the Green Bay NWS Office

More study will be done on these events. But it’s already clear this was one of the most intense and widespread severe storm outbreaks on record in the Upper Midwest.

Weather and Climate News

Updraft® - Minnesota Weather News

Paul Huttner

Author

Severe storms ripped through Minnesota and Wisconsin Friday and Saturday.

NOAA radar loop in northern Wisconsin from Friday July 19.

Dueling Derechos: Anatomy of weekend "macrobursts"

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