Radar Meteorology AOS 444 October 28, 2002 Laboratory 6: WATADS study of Oakfield tornado from KGRB

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Radar Meteorology AOS 444 October 28, 2002 Laboratory 6: WATADS study of Oakfield tornado from KGRB YOUR NAME: YOUR PARTNER S NAME: On July 18, 1996 the town of Oakfield, Wisconsin was all but

1 Radar Meteorology AOS 444 October 28, 2002 Laboratory 6: WATADS study of Oakfield tornado from KGRB YOUR NAME: YOUR PARTNER S NAME: 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 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 (report from CIMSS) 1

2 OBJECTIVE OF THIS LAB: To continue familiarizing yourself with the WATADS software and have you look at data from the Green Bay (KGRB), WI, WSR-88D from July 18 th, 96. This data contains the entire evolution of the cell that produced the "Oakfield tornado". A comprehensive data archive prepared by COMET of NOAA is made available available at: where you can find satellite and other observations. You can also find upper air analyses of this case at: To run the WATADS program: 1) simply type, watads, at the prompt. 2) once the menu bar comes up on the left, select "Open Existing Data Directory", choose the filename that contains "oakfield" 3) next, select "Run RADS Image Display Program" Notes: 1) Do not start this program while you have Netscape running. You may open Netscape after you have started the Watads program. 2) When doing loops, you can only load 20 images at a time 3) Go to "Prefer" on the top menu bar and click on "Alarm" to turn it off. This will get rid of a lot of useless, annoying messages that pop up 4) Mouse instructions for the various tools in this program are located at the top of each window 1. Briefly characterize the synoptic situation leading to this event, i.e. approaching cold front, upper level trough, cyclone, etc Using WATADS, identify the thunderstorm cell number that spawned the Oakfield tornado.. 3. Describe the location, shape, size, duration, and evolution of the thunderstorm that spawned the Oakfield tornado. Use diagrams as necessary. 2

3 4. Does the WSR-88D identify a meso-cyclone, i.e. a supercell, prior to the tornado? At what time prior to the tornado (7:15)? What is the diameter of the meso-cyclone? (Give a time please) How is it different from other meso-cyclones identified on this day (i.e. strength, size, relative location to others, etc...)? 5. Did the WSR88D identify a TVS prior to the tornado (7:15)? At what time and location? What was the strongest gate-to-gate shear associated with this vortex? What time was this shear observed? How did the height of strongest gate-to-gate shear change with time? (Look at "Trends", Go to sets~torn) What does this indicate? 6. What is the storm top of the tornadic cell before the tornado (in feet and km) and how does that storm top height change as the tornado evolves? (Usually one expects a high overshooting top to collapse just as the tornado develops; do you see that happening? To examine this, you can either look at the "trends" feature or draw a cross-section through the meso-cyclone in each image). 3

4 7. Can you find a BWER or a WER associated with the primary mesocyclone (Oakfield cell)? What is the highest elevation of the WER? What is the physical mechanism that produces a WER (refer to knowledge from last lab)? 8. How deep is the TVS? How does its diameter change with height? How does its depth change with time? 9. Can you find any severe (> 55 kts) straight line winds associated with the thunderstorm system? How strong and from what direction? What meso-scale feature are these winds associated with? 10. Can you identify hail reaching the surface? Where relative to the mesocyclone? Draw a diagram: 4

5 11. Sketch a hodograph of the flow observed just prior to the tornado in the undisturbed inflow region of the storm. 12. Sketch a cross-section from the south-east to the north west through the mesocyclone associated with the TVS. Show regions of hail, rain and snow, the WER and the flow in that plane based on the WSR88D observations. Label length and height dimensions of your cross section. 5

The Oakfield, Wisconsin, Tornado from July Brett Berenz Student at the University of Wisconsin

The Oakfield, Wisconsin, Tornado from 18-19 July 1996 Brett Berenz Student at the University of Wisconsin Abstract On July 18 th, 1996 an F5 tornado affected the region of Oakfield, Wisconsin. Leading