For story with photos visit: http://www.crh.noaa.gov/news/display_cmsstory.php?wfo=mkx&storyid=71794&source=0
Quick Facts:
What: one weak tornado
Where: somewhere on Lake Monona in Madison, WI
When: around 715 pm to 720 pm CDT
Injuries: none
Fatalities: none
Damage: none - it was over water
Strength: EF0 with winds no more than 65 mph
Duration: unknown at this time
2011 Wisconsin Tornado Count = 32
What we know:
A weak tornado (EF0) spun up on Lake Monona around 715 pm CDT, Monday evening, August 8, 2011.
It was seen by many people, and several individuals took pictures of it, and at least a couple video clips of the tornado were posted on Madison TV stations.
The associated "funnel cloud" was probably in existence for 10 to 15 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 inujuries, fatalities, or damage.
There was no tornado warning - WSR-88D Doppler radar did not have any rotation within the responsible cloud.
There were no thunderstorms in the Madison area at the time of the weak tornado.
The tornado was associated with a convective rain shower moving southeast over Lake Monona. In other words, this was a non-supercell tornado. Most likely the updraft of the rain shower, with the tornado below the rain-free base, was just to the north 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.
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.
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 bouyancy which resulted in the circulation being raised vertically. The circulation was grabbed and stretched vertically into the cloud base by the updraft of the cumulus cloud above. Veritical stretching of a circulation results in an increase in rotational speeds of the circulation. Tornado formation via this method is refered to by some people as a landspout situation - where the tornado literally spins up from the ground up to cloud base.
Eventually, invisible water vapour within the rotating column of air condensed into a visible funnel-shaped cloud entitled "condensation funnel." Since atmospheric pressure is lower the higher one goes, the condensation funnel developed initiallly near cloud base and then developed downward about half-way to the water surface. [In order to get a visibie cloud to develop one needs invisibile water vapour to condense onto tiny dust, dirt, clay, or salt particles in a region where there is lower atmospheric pressure]
Below is an image illistrating the "landspout" process by which the Lake Monona tornado came to be. Click on image for larger version.
What still needs to be done:
The NWS is required to document the starting and ending times and locations of a variety of weather hazards - including tornadoes. We need your help in completely documenting the Lake Monona tornado. Send your information to: [email protected].
If you observed the tornado - what was the time the water-spray at the bottom of the tornado became evident? How long the tornado last - how many minutes did the rotating water-spray persist? We need this information to the nearest minute.
What was the beginning and ending location of the tornado? Where did it occur? Based on the pictures and video we've seen, it appears the tornado was in the northeast corner of Lake Monona, but we could be wrong. Below is a map of the Madison and Lake Monona area. The "X" represents the location of some of the hpeople who took pictures and video of the tornado. The "T" represents possible locations of the tornado. Which location works best for what you saw? Or - is there a better location?
Feel free to draw a line on the map below to show us your best guess of what the tornado path looked like - and e-mail it back to us at: [email protected]. You can also annotate the beginning and ending times of the tornado, if you are confident. Evidence through 525 pm, August 9th, suggests the tornado occurred in the southeast part of Lake Monona.
Click on image for larger version.
If you took a picture of the tornado - would you be willing to share it with us? We'd like to post your picture within this Top News of the Day story. We would put your name on your picture to give you credit.
Any information you have can be e-mailed to: [email protected]
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.
Below are three pictures sent to WKOW-27 and forwarded by Bob Lindmeier, Chief Meteorologist. Thank you folks! In the pictures taken 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.
The Difference Between a Waterspout and a Tornado:
Scientifically, there is no difference - they are one 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.
So why have we avoided calling the Lake Monona event a waterspout? Good question. It's strictly an internal, NWS technicality. If the tornado occurred over a body of water that had assigned, geographical areas or zones, it is documented as a waterspout in the NWS's Storm Data publication. This would include the oceanic areas, all of the Great Lakes and adjoining bays, and some other large inland lakes. None of the inland lakes in Wisconsin have assigned, geographical areas or zones. Therefore, any tornado that starts over or moves across an inland lake is documented as a tornado.
So, in lay-mens terms, there was a waterspout on Lake Monona, but for NWS documentation purposes, it will go down as a tornado. It just depends on whose classes you are looking through.
Lessons You Should Learn From This Event:
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 indentify the initial circulation of a tornado that develops via the landspout method as illustrated above.
5. The condensation funnel intially 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 tornado.
Source: http://www.crh.noaa.gov/news/display_cmsstory.php?wfo=mkx&storyid=71794&source=0