Tornado Case Study

*** The Oakfield, Wisconsin Case Study ***


The purpose of this site is to analyze a severe weather event using many general scientific applications used by meteorologists. It can also be viewed as a hands on exercise to forecasting the weather, as it focuses on the events and data that spawned a devastating tornado that struck Oakfield, Wisconsin on July 18th, 1996. Analyzing satellite images, Doppler radar, and contoured surface/upper-air data will give a thorough understanding of what conditions led to the severe thunderstorms which roared across the upper-Midwest (clicking on any weather related terms will provide a meteorological dictionary).

This web page can provide the following activities for students, teachers, and weather enthusiasts.

  • Mesoscale forecasting and analysis.
  • Contour analysis and interpretation.
  • Satellite and radar image interpretation.
  • Analysis of a severe weather event.

On July 18, 1996 the town of Oakfield, Wisconsin was all but destroyed by a powerful tornado. In addition to the tornado, strong thunderstorms brought heavy rains, lightning, and gusty winds to the region. All of these elements resulted from the passage of a cold front. The violent tornado developed in Fond du Lac County and moved southeastward across Wisconsin taking direct aim at Oakfield. At 7:15 PM the large tornado struck the 1,000 person town, injuring 17 people. Damage estimates totaled over $40 million as 47 of 320 homes were destroyed. In addition, 56 homes as well as numerous businesses and churches sustained heavy damage. A "state of emergency" was declared by Governor Tommy Thompson allowing National Guard soldiers to be called in to aid victims and clear debris.

The tornado was powerful enough to level the Friday Canning Company, while picking up millions of empty cans and leaving them sprawled over a 50 mile distance. Besides structural damage to buildings the tornado was quite costly to farmers; Crops, livestock, and farm equipment were also destroyed. The original National Weather Service report from Milwaukee/Sullivan categorized the tornado to be a F3 to F4, winds of 158-260 mph, although it was later upgraded to an F5, winds greater than 261 mph, the most severe tornado possible. F5 tornadoes are very rare, only occurring, on average, every other year in the United States. The F5 status was issued based on the inspection of the damage in the Oakfield area. National Weather Service (NWS) tornadic storm warnings of the Oakfield tornado can be viewed NWS Oakfield Tornado Report. When a tornado watch is issued, conditions are favorable for the formation of tornadoes. A warning is issued when an actual tornado has been reported. The tornado stayed on the ground for over 20 minutes as it moved southeastward for nearly 20 miles before finally dissipating. This photograph, taken by Wayne Feltz, shows the thunderstorm that spawned the Oakfield tornado as it passes to the north of Madison, WI.

Much can be learned about meteorology from studying the Oakfield tornado. Many factors important for predicting the weather will be thoroughly discussed, using data from this storm to aid in understanding the atmosphere.

For students and teachers who are interested in contour analysis and interpretation, parts one and two of the index should be the main focus, especially the exercise available in the first paragraph of the contouring section. Sections three and four focus on satellite and radar interpretation. All section will be useful for those interested in mesoscale analysis and investigating the severe weather event.


INDEX

I. Cyclone: A General Overview of What Caused The Storms

  • Movement of air in cyclones

II. Contouring of Surface and Upper-air Data

A new interactive contour analysis excercise has been added (you draw the lines using the mouse).

A) Continental United States:

B) Mesoscale Analysis- Midwest:

III. Satellite Images

IV. Doppler Radar



The Oakfield tornado case study is also available as an educational packet for high school students. Introductory information on understanding the atmosphere and weather, as well as contouring, satellite, and radar analysis is included. Teachers or students who wish to find out more about this packet can call the University of Wisconsin-Madison's(UW) Cooperate Institute for Meteorological Satellite Studies (CIMSS) at (608)-263-7435.


This page was developed and constructed by Rhett Grauman through support from NOAA grant NA67EC0100.

This page was assembled with help from the following CIMSS and UW-Madison AOS scientists.

  • Tom Achtor
  • John Mecikalski
  • Scott Bachmeier
  • Mark Whipple
  • Pete Polkrandt
  • Ray Garcia
  • Wayne Feltz
  • Joleen Feltz
  • Tony Wendricks

The above photos of the Oakfield tornado were taken by stormchaser Cailyn Lloyd. To see more outstanding photos of the Oakfield tornado as well as many others check out her web page.


Any questions or comments can be sent to

jasonb@ssec.wisc.edu or toma@ssec.wisc.edu

High school teachers and students who are interested in meteorology, Earth, and space sciences are invited to apply for the week long Wisconsin Space Grant Consortium summer workshop which introduces many of these exiting topics with hands on activities. For more information: Summer Workshop

March 2012 Outbreak

On March 2, 2012, a large tornado outbreak devastated parts of the South and Ohio River Valley. Over 120 tornadoes (preliminary numbers) were reported, along with over 500 other severe weather reports, including hail and high winds. Unfortunately, this storm system also resulted in at least 39 fatalities. We’re going to take a closer look at how the storm system evolved and created such destructive and deadly tornadoes.

Storm System Animation

Visualization Description: This first visualization is an animation of IR satellite imagery over a 48-hour period. The animation starts at 6pm CST on March 1, 2012, the day before the massive early-season tornado outbreak. As the animation approaches March 2, the area of interest is highlighted. A clock will also appear and be displayed for the entirety of March 2nd. As the animation progresses, a low pressure “L” symbol will also move across the area of interest from about 7am through 9:30pm CST, the time period that most of the storm activity occurred. Following the low pressure movement, red dots, representing tornado reports, appear along with a gray base map. For SOS veterans, it should be noted that the IR animation will seem particularly slow. I slowed it down a lot to allow time to see the relatively fast moving storm system.

About the Data: It’s possible that the warmer than normal winter in much of the U.S. contributed to this earlier than normal severe weather outbreak. Weather and climate scientists suggest that warmer than normal sea surface temperatures (about 1˚C above normal) across the Gulf of Mexico played a part in fueling the severe weather. As warm moist air moved northward out of the Gulf of Mexico, cold dry air moved southeast out of Canada. You can even see the cold front in the IR satellite imagery, draping southwest from the low pressure symbol.

As the cold dry air at higher altitudes and warm moist air collide, the atmosphere became very unstable. Moist air (and warm air) is less dense than the cold dry air and is therefore forced upward as columns of air into thunderstorms, called updrafts. At this point, we still don’t have tornadoes, however. The air in the storms needs to become “twisted” by something called shear, when the winds at various levels of the atmosphere change speed and direction. This is in place this day as well, in part because of an enhanced jet stream. Cue the next dataset!

Water Vapor Satellite Imagery

Visualization Description: Many of you are probably already familiar with the water vapor satellite dataset. I’ll spare you the details. But, here’s a quick reminder: We’re looking at a higher level of the atmosphere and basically visualizing where dry air is and where moist air is, not necessarily where there are clouds and no clouds. Darker areas indicate dry air where whiter areas indicate moist air. I have also included a PIP of upper level wind speeds. I’ll get to that below.

About the Data:

Water vapor satellite imagery is commonly used by meteorologists to locate the jet stream. Here, we are trying to find the darker (dry air) stream of air forming a U-shape trough across the center of the country. The strongest part moves across the stormy area from southwest to northeast. To help further showcase the jet stream here, the PIP (created by the NOAA Environmental Visualization Lab) for this visualization shows wind speeds at 18,000 feet up in the atmosphere. The image is from 6:00 pm CST. You can clearly see the strongest winds (up to 120 mph) are right over the area with the most storm reports.

These strong upper level winds not only provide the aforementioned shear, but also allow air columns to rise more efficiently into thunderstorms. As air is evacuated above, lower level air is “sucked” up into the storm. You may have noticed how on a windy evening, smoke from your chimney more efficiently rises out up and out. It’s a similar situation here.

All of these conditions are exactly what meteorologists are looking for with regards to severe storm (and tornado) development: instability and lift, shear, and moist air. Having severe weather in early March is not unheard of. Having such severe weather and that many storms in March is definitely rare and may be attributed to the warmer than normal winter for the eastern United States.

Wow! This is a much longer blog post than normal, but isn’t it interesting? This entry will also be posted in the “Earth 101” section of the website for future reference regarding tornadoes. That’s all for now. The next post will be the March Climate Digest.

Other Relevant Resources

Here are some other cool resources regarding severe weather that weren’t necessarily used in this week’s EarthNow post.

The first link is brand new and is regarding the new Dual-Polarization Doppler Radars, currently being installed at National Weather Service Forecast Offices around the country. One great advancement will be even better detection of tornadoes.

Dual-Polarization Radar by NOAA Environmental Visualization Lab

Cooking Up a Storm: an SOS movie by NOAA Severe Storms Lab

Where do I find the datasets?

  • First, check your SOS system to make sure it’s not already in the EarthNow category. There should also be an ‘earthnow.sos’ playlist file (you’ll need to add that to your sosrc folder).
  • If not, you can download the datasets and playlist.sos files from this FTP Site.
Reviewed by:
Stephen Corfidi, Lead Forecaster, NOAA Storm Prediction Center
Credits:
Rick Kohrs, Cooperative Institute for Meteorological Satellite Studies
Dan Pisut, NOAA Environmental Visualization Lab
Patrick Rowley, Cooperative Institute for Meteorological Satellite Studies
References:
AccuWeather, The Science Behind the Tornado Outbreak, http://www.accuweather.com/en/weather-news/the-science-behind-the-tornado/62355
NOAA Environmental Visualization Lab, http://www.nnvl.noaa.gov/MediaDetail2.php?MediaID=1002&MediaTypeID=1
NOAA National Climatic Data Center, State of the Climate: Global Hazards for March 2012, published online April 2012, retrieved on April 5, 2012 from http://www.ncdc.noaa.gov/sotc/hazards/2012/3.
NOAA Storm Prediction Center, http://www.spc.noaa.gov/exper/archive/event.php?date=20120302
Wunderground, Dr. Jeff Masters’ Wunderblog, http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2045
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