Final Report on Weak Waterspout-Tornado on Lake Monona August 8, 2011

This is a final report.  The time and location (path) of this weak waterspout-tornado constitute the "best-fit" and "averaging" of numerous eyewitness reports, pictures, and video evidence.  The NWS appreciates the contributions from Dale Berstein, President of the MidWest Severe Storm Tracking/Response Center (SSTRC) who taliked to several people on the shoreline, and Don Sanford, Captain of the Betty Lou Cruise Line, who was very close to the waterspout-tornado and took video of it.  Utilizing their information, we were able to make sense of all other reports and pictures in order to determine the path and times of this event.  Also - we wish to acknowledge the contributions and pictures forwarded by WKOW TV-27 and WMTV TV-15 in Madison and many other individuals.  Some of their pictures are seen below.     ...Rusty Kapela, WCM

Quick Facts:

What: one weak waterspout-tornado

Where: southern part of Lake Monona in Dane County

When: August 8, 2011 - 713 pm to 722 pm CDT

Injuries: none

Fatalities: none

Damage: none - it was over water

Strength: EF0- no fesible way to estimate winds

Path Length - 1.24 miles

Max Path Width - 20 yards

2011 Wisconsin Tornado Count = 33 (as of 08/23/11)


 

Path of the Waterspout-tornado:

Below is a map showing our best estimate of the waterspout-tornado path on Lake Monona, based on many eyewitness reports from the general public.  Click on image for larger version.

final tor path

What we know:

A weak waterspout-tornado (EF0) spun up on Lake Monona around 713 pm CDT, Monday evening, August 8, 2011, and made landfall and quickly dissipated.

It was seen by many people, and several individuals took pictures and/or video of it.

The associated "funnel cloud" was probably in existence for a few minutes prior to the tornado spin-up (rotating air column extending from the ground or water surface to the base of a convective cloud).

There were no injuries, fatalities, or damage.

There was no tornado warning - WSR-88D Doppler radar did not have any rotation within the responsible cloud, and waterspout-tornadoes are very weak and result in minimal damage.  In a sense, this event did not constitute a public safety issue.

There were no thunderstorms in the Madison area at the time of the weak tornado.

The waterspout-tornado was associated with a convective rain shower moving south-southeast over Lake Monona.  In other words, this was a non-supercell, waterspout-tornado.  Most likely the updraft of the rain shower, with the waterspout-tornado below the rain-free base, was just to the north-northeast of the precipitation.  Below are two radar images showing the location of the rain shower relative to Lake Monona, with one image zoomed into the Madison area and the other one showing the overall pattern across all of southern Wisconsin.  Click on images for larger version.

715 pm radar image - zoomed to Madison  715 pm radar image southern WI

The surface weather map depicted a weak surface frontal boundary lying west to east across the Lake Monona area.  Below are two images showing the frontal boundary at 7 pm CST - one zoomed into the Madison area and the other of all of south-central and southeast Wisconsin.  Click on images for larger version.

Wx Map - Madison area  Wx Map - SE & SC WI

How it happened:

Converging winds into the frontal boundary allowed for the generation of a weak, invisible circulation along that boundary.  The air below cloud base had buoyancy which resulted in the circulation being raised vertically while additional heat and moisture rose from the water surface.  The circulation was grabbed and stretched vertically into the cloud base by the updraft of the cumulus cloud above.  Vertical stretching of a circulation results in an increase in rotational speeds of the circulation.  Tornado formation via this method is referred to by some people as a landspout situation - where the tornado literally spins up from the ground to the cloud base.

Eventually, invisible water vapor within the rotating column of air condensed into a visible funnel-shaped cloud called a "condensation funnel."   Since atmospheric pressure is lower the higher one goes, the condensation funnel developed initially near cloud base and then developed downward about half-way to the water surface. [In order to get a visible cloud to develop, one needs invisible water vapor to condense onto tiny dust, dirt, clay, or salt particles in a region where there is lower atmospheric pressure.]

Below is an image illustrating the "landspout" process by which the Lake Monona waterspout-tornado came to be.  This same mechanism is responsible for the majority of waterspouts on Lake Michigan.  Click on image for larger version.

 Landspout Method

Pictures of the Waterspout-tornado:

Below is the first picture sent to us by Nathan Connell.  He was on the Capitol Square looking southeast over Lake Monona at about 719 pm.  He said the water-spray was still evident at that time.  Thanks Nathan!  Click on image for larger version.

Nathan Tor Pic 719 pm

Below are three pictures sent to WKOW-27 and forwarded by Bob Lindmeier, Chief Meteorologist.  Thank you folks!  In the pictures taken by Christopher Kelly and Susan Tessmann, note the wind disturbance pattern on the water surface.  Wind convergence is clearly shown.  Click on image for larger version.

tor pic Chris Kelly  tor pic Susan Tessmann  tor pic Dave Braund

Below are three pictures taken by Steve Brown who lives near the shoreline in the far northeast corner of Lake Monona. His camera time stamp was 720 pm, and he places the tornado in the southern part of the lake at that time and moving slowly east.  Click on images for larger versions.

Steve Brown 1  Steve Brown 2  Steve Brown 3

Below are pictures taken by Chris Wisswell at the end of the waterspout-tornado event was in the Squaw Bay area.  Chris annoted on his images in order to point out some features.  Click on image for larger version.

Wisswell 1  Wisswell 2

Wisswell 3  Wisswell 4

Additional pictures follow.  The umbrella was lofted 20 feet into the air by brisk south winds and deposited on the roof of the home which was located where the letter U is shown in the map above.  The home sits on higher land on Waunona Way on the south shore of Lake Monona.  It was lofted as the waterspout-tornado approached.  Click on images for larger version.

Rich Guild 1  KG - umbrella lofted  Don Sanford 1

Don Sanford 2  Jerrold Robaidek 2

Below are a couple pictures taken by Ben Miler of the event as it ended.  Note the verical development of the cumulus cloud and that there was no rain with the cloud.  Apparently the cumulus cloud generated one last funnel cloud southeast of Lake Monona about 15 minutes after the waterspout-tornado had ended.

Ben Miller 1  Ben Miller 2

The Difference Between a Waterspout and a Tornado:

Scientifically, there is no difference - they are one and the same.  They are both defined as a violently rotating column of air extending from the ground or water surface to the base of a convective cloud.  However, over the years, any tornado over a body of water came to be known as a waterspout.

In most waterspout-tornado situations on Lake Michigan, the vortex usually develops via the landspout-waterspout method outlined above in the absence of thunderstorms.  These types of vortices are usually weaker compared to the thunderstorm-associated tornadoes.   Of course, a thunderstorm-associated tornado (usually of the supercell variety) can travel from a land surface onto a water surface, whether it be an inland lake or Lake Michigan.

The Lake Monona case was one of the weaker, non-thunderstorm waterspout-tornadoes.

Take-away Lessons:

 1.  You don't need a thunderstorm in order to have a tornado.

2.  Tornadoes can spin up from the ground (initially invisible).

3.  The condensation funnel does not have to touch the ground in order to have a tornado.  Some tornadoes have very little, if any, condensation funnel, but damage is occurring on the ground.  In other words, the condensation funnel "sits inside" the rotating column of air that is the tornado. You can't see the rotating column of air until you have a condensation funnel or you see a rotating water-spray over a water body or a rotating dirt/debris spray over the ground.  Of course, if the condensation funnel develops all the way to the ground or water surface, it makes the tornado recognition process much easier!  Now, try doing this at night!

4.  Doppler radar will not identify the initial circulation of a waterspout-tornado that develops via the landspout method as illustrated above.

5. The condensation funnel initially develops near cloud base where it is easier to reach saturation due to lower atmospheric pressure.

6.  Tornadoes do not avoid lakes, rivers, swamps, mountains, hills, ridges, or tall skyscrapers in large cities (these geographical features do not split storms apart).  If weather conditions come together properly, you will have a tornado.



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