Cold air aloft over Wisconsin in combination with daytime heating resulted in widely scattered thunderstorm development across southcentral and southeast Wisconsin...including Lake Michigan.
The freezing level (0C) in the atmosphere was a low 8700 feet above ground level Sunday afternoon, while 18,000 feet above ground level it was -18C (-0.4F). WSR-88D Doppler Radar suggested the tops of the strongest storms reached about 30 to 35,000 feet above ground level. This combination allowed for generation of hail stones up to 1.75 inches in diameter, heavy rains of 3/4 to 1.50 inches within an hour or so, gusty winds to around 45 mph, low cloud bases, and scary-looking clouds.
Below are two pictures via Twitter from @LukeSampe in the Grafton area of Ozaukee County. The golf-ball size hail (1.75") fell shortly after a Severe Thunderstorm Warning was issued for a portion of Ozaukee County. The radar image is at 448 pm, just a couple minutes before the large hail reached the ground.
The Chief Meteorologists at WITI TV-6 (Vince Condella) and WISN TV-12 (Mark Baden) in Milwaukee relayed to our office some cloud pictures of the storms and scary-lookng cloud fragments. These pictures were submitted by their viewers, and will eventually find their way into the Scary Looking Cloud Club (see link at bottom of this story).
Below are two pictures submitted to WITI TV-6 by Amy Zimmerman as she was driving into Milwaukee. Click on images for larger version.
Below is a picture submitted to WITI TV-6 by John Detienne, in Oostburg looking north towards Sheboygan. Click on image for larger version.
Below is a picture submitted by Morgan Kath (Sheboygan Falls) to WISN TV-12. Click on image for larger version.
Below is a picture taken by Sarah Ruby at about 730 pm at a location 10 miles south of Plymouth, Sheboygan Co., on State Highway 57. In the picture is ia classic shelft cloud on the front side of the storm. The picture was forwarded to our office by Meteorologist Fish at WTMJ4. Click on image for larger version.
Ultimately, the thunderstorms over Ozaukee County moved south into Milwaukee County and generated an awesome shelf cloud. Below are a couple pictures of the shelf cloud taken by @TomPurdyWI and a radar animation showing the thunderstorms over Ozaukee County moving towards downtown Milwaukee. The radar animation spans from 4:58 PM to 5:59 PM. Click any of the below figures/animation to see it enlarged.
Below are the individual images that make up the previous radar animation.
Below is a neat picture of downtown Milwaukee that was Tweeted by Kaitlyn Herzog (@KaitlynMKE).
Below is a picture of a double-rainbow taken and tweeted by @tosasoccerdad.
Low-hanging cloud fragments at the bases of storms may look scary to some people. Experience has shown that when some people get scared by clouds they call the 911 Dispatchers at Comms Centers in Sheriff Departments and report them as funnel clouds or even tornadoes!
A more detailed explanation of scary-looking clouds can be found here.
Kapela/ET, WFO Milwaukee
Looking at radar estimated rainfall from our new Dual Polarization capability and the legacy calculations, it appears that about 70-80% of the southern WI area received rainfall today. Some of the heavier amounts, likely exceeding 1 inch, are in the green shades on the images below. Rainfall above 0.50" appears in the blue shade. Some spots that received the heavier amounts include eastern Marquette County, northern Green Lake County, eastern Fond du Lac and western Sheboygan Counties, along with eastern Dane County. Another area with heavy rainfall and quite a bit of hail was in central Ozaukee County, where golfball hail and about 1.5" of rain was observed near Grafton.
The image on the left is the old legacy Doppler Radar estimate and on the right is the Dual Polarization estimate for the 12 hour rainfall ending about 8 pm August 19th.
Jeff Craven, Science and Operations Officer
National Weather Service Milwaukee/Sullivan WI