June 21, 2013 Storm Summary: Shelf Cloud & Wake Low (updated 6/28)

Updated 6/28/13 to include weather instrumentation graphic from UW-Madison campus.

Friday, June 21st was the summer solstice - the longest "day" of the year.  Appropriately, a Severe Thunderstorm Watch was issued for portions of southern Wisconsin Friday morning.  A line of strong to severe storms developed over Minnesota and proceeded to move southeast through southern Wisconsin.

Three interesting things happened on Friday:

  • Line of storms generated northwest wind gusts of 35 mph to around 60 mph.
  • The line of storms generated a shelf cloud that was photographed and initiated a false funnel cloud report.
  • A wake low developed behind the line of storms and resulted in southeast to south winds gusting to 35 to 45 mph. 

Severe wind gusts to around 60 mph knocked some trees down in the Avoca area in northwest Iowa County.  Otherwise, as the line of storms moved east-southeast across southern Wisconsin it generated wind gusts of 40 to 50 mph.  We did get a few reports of small broken tree branches that led to scattered power outages.  Additionally, brief moderate to heavy rains accompanied the storms leading to some ponding of water in low spots and road side ditches.  In some cases, a half inch of rain fell in 30 minutes or less. Sherm (KB9Q) at 1.0N Big Bend in Waukesha County picked up 0.90 inches as the storms rolled through.

At the NWS Milwaukee/Sullivan office we had a peak northwest wind gust of 26 mph when the storms moved through and picked up 0.62 inch of rain.  Our temperature dropped from 76 to 65 as well.

Below, on the left, is a composite image showing the position of the line of storms at 817 am CDT and 1056 am CDT, as well as an infrared satellite picture at 845 am CDT.  Note the enormous size of the cloud-top canopy of the meso-scale convective complex.  It covered the entire state of Wisconsin!  The image on the right shows a surface plot of weather observations at 1 pm.  The center of the wake low is indicated by the red "L."  The position of the line of storms is indicated by the dashed line in the Chicago area.  The meso-high pressure generated by the leftover rain-cooled air is indicated by the "H."   The red arrow indicates the area of strong gusty southeast to south winds in the region of a tight pressure gradient behind the line of storms.  Click on the image for a larger version.

Radar & Satellite Pictures  Surface Plot 1 pm

In general, the wake-low winds out of the southeast to south direction gusted to 35 to 45 mph for a couple of hours.

Our friends over at the15-story Atmospheric, Oceanic, and Space Sciences building on the University of Wisconsin - Madison campus shared the following graphic plot of weather instrumentation on the roof.  The peak gust on the roof was out of the south-southeast at 35 knots (40 mph) at 1259 pm CDT.   Note the gusty wind period corresponding the the steady drop in air pressure.  Click on the image for a larger version.

AOS instrument graphic

The line of storms had a well-defined shelf cloud on the front side, which was photographed by several people, some of them severe weather spotters. Below are a few composite images.  Click on images for larger versions.

Triple Shelf Quad 1 Shelf Clouds  Quad 2 Shlf 21 June 2013

As expected, the shelf cloud scared some people enough to make them think they were looking at a funnel cloud. Typically these are people who have never attended a severe weather spotter class.  Consequently, they are unaware that lines of storms and shelf clouds sometimes have cloud fragments that briefly resemble funnel clouds. Sure enough, one of the County 911 Comms Centers in southeast Wisconsin received a call from a private citizen who reported a funnel cloud.

Below is an image with two pictures sent in to WITI TV-6 in Milwaukee of the shelf cloud in Walworth County.  Take a close look and you will see a "false" funnel cloud in both pictures.  The "false" funnel is actually the top of one of the plates or layers that comprise the shelf cloud.  The angle or perspective of the camera gives one the false impression of a funnel cloud.  These two pictures are among the best Scary-Looking Cloud examples we've ever seen!  Click on image for larger version.

Double Shelft 21 June 2013

Back in 2009, we started the Scary-Looking Cloud Club in order to display pictures of scary-looking clouds (SLC) and define tornadoes, funnel clouds and SLCs.  Please help us spread the word by telling your family, relatives, friends, and co-workers about the Scary-Looking Cloud Club.


Kapela, WFO Milwaukee/Sullivan 


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