The F5 Oakfield Tornado

This violent tornado struck the village of Oakfield at 7:15pm after it touched down 4 miles WNW of the village. During its approach on Oakfield it intensified to a F3 rating. When it tore through the village it intensified to a F4, but along its path 1 to 4 miles east of the village it intensified to F5 strength (estimated 265 mph winds).

In this span 4 homes were completely swept clean off their foundations and a couple automobiles became airborne missiles for a distance of about 400 feet. The core width of the most intense damage was about 150 to 200 yards, although at times, some secondary damage was observed in a 400 yard wide path. Oakfield residents heard local sirens about 8 minutes before the tornado entered the village.

Miraculously, no one was killed, but there were 12 injuries. Some of the injured were hospitalized. Along the tornado's path, 60 homes and 6 businesses were destroyed. An additional 130 homes and businesses were damaged. In Oakfield, a commercial canning company was devastated. Two churches in the village were also destroyed, as well as numerous vehicles. In the rural areas along the tornado's path, 18 barns and many sheds were destroyed or damaged, and about 500 acres of crops were wiped out. Total damage amounts were $39.5 million in public/private property, and $900,000 in crop losses. Residents reported that they had difficulty "popping" their ears as the tornado roared through their neighborhood.

July 18, 1996 was a classic tornado setup for Wisconsin or anywhere else in the US. A hot and humid day which featured all of the ingredients of severe thunderstorms.  

The upper levels of the atmosphere had the forcing and wind speed/shear elements that you need for supercell thunderstorms. At 500mb (image on the right), a 50-60kt jet streak was in place across central Wisconsin out of the west-northwest along with shortwave troughing at this level.

With low level winds being out of the south-southwest at 10-15kts, this led to ideal deep wind shear of 50 to 65 kts out ahead of where the storms would develop that day.

At the surface (see below), a developing low pressure system was tracking across northern Wisconsin with a warm front extending east through the Great Lakes and a trailing cold front that ended up being the lifting/focus mechanism for storm development in the late afternoon/early evening hours. Out ahead of the cold front was a trough which also helped to develop some lead supercell thunderstorms out in the prime environment for tornadic development.

Another key ingredient of this setup was the high instability that developed that afternoon due to the hot and humid air mass south of the low pressure system and colder air aloft due to the mid level trough. Surface based CAPE rose into the 4,000 J/kg range that afternoon with the main supercell thunderstorm developing at the nose of this instability axis.

Below is the sounding (weather balloon) data from Green Bay from right about the time that the Oakfield tornado occurred. Some features of note are the CAPE profile (far right dotted line) showing measured Surface Based CAPE of 3400 J/kg. Winds at the surface are around 10kts out of the SW while mid level winds increase and veer on up to about 60 knots out of the WNW in the mid to upper levels.

National Weather Service meteorologists were very much aware that there was a potential for severe weather on July 18th, 1996. Forecast models were showing the environmental elements coming together to possibly produce a severe weather event. The main question and uncertainty with the potential severe weather was with whether or not a layer of warm air above the ground called the "cap" would break. This "cap" is what normally prevents upward motions which normally would help develop thunderstorms. The "cap" did break over central Wisconsin where a supercell thunderstorm would develop and go on to produce the Oakfield tornado. Below are some of the Storm Prediction Center forecasts and discussions leading up to the tornado. A Moderate Risk for severe weather was issued by the SPC for this day.

The National Weather Service Milwaukee/Sullivan office also was tuned into the potential of a severe weather event, but there were concerns that it possibly wouldn't happen. The picture on the right is of retired NWS Milwaukee Lead Forecaster Steve Hentz who happened to be the short term forecaster and issuer of warnings that day. Below are some of the State Forecast Discussions issued on July 18th, 1996.

At 3:33pm, the first Tornado Watch Was issued for much of Wisconsin. A second Tornado Watch was issued at 6:47pm to extend the watch to cover the rest of far eastern Wisconsin which didn't go into the initial watch.

Archived radar is only available from KGRB in Green Bay as the archive option wasn't on from the KMKX Milwaukee/Sullivan radar. The radar data shows a classic cyclic supercell that helped to produce the violent tornado in Oakfield. This storm started out in eastern Adams county and produced its first tornado in Green Lake county before tracking through southern Fond du Lac county and producing the Oakfield F5 tornado. The same storm ended up going through Ozaukee county and produced two more tornadoes near Port Washington. In total, 12 tornadoes occurred across the state on July 18th, 1996. Below is the reflectivity and velocity data associated first with the Oakfield F5 tornado and then all of the other tornadoes from the day.

The NWS Milwaukee/Sullivan office ended up issuing 13 Tornado Warnings and 10 Severe Thunderstorm Warnings on this day. The Tornado Warning for the Oakfield F5 tornado was issued at 7:09pm as it developed west of Oakfield. The tornado ended up hitting Oakfield at 7:15pm, which gave residents about 6-8 minutes to get to their shelters.

Radar data from KGRB shows that the Oakfield tornado spawned from a lead supercell thunderstorm that developed out ahead of the main boundary/cold front. This was a cyclic supercell as it first produced a tornado near Green Lake, then spawned the Oakfield tornado. Later, that same supercell produced two more tornadoes near Fredonia and Port Washington in Ozaukee county.

The left side of the loop shows the base/0.5 degree level reflectivity. Reflectivity is essentially the measure of how much 'stuff' is out there. The data from this loop shows a classic reflectivity pattern for a supercell thunderstorm with a hook echo in the vicinity of where the tornadoes occurred, particularly near Oakfield. This area is the updraft portion of the thunderstorm and where the warm, moist air near the ground gets transported up through the thunderstorm.  

The right side of the loop shows the base/0.5 degree velocity. The velocity field uses the doppler effect to show where potential rotation is occurring in a thunderstorm. Much like a police siren sound wave that changes as it comes toward you vs when it is moving away, doppler radar works the same way with being able to sense whether or not an object is moving toward or away from the radar. Objects/rain drops moving toward the radar get painted green or blue on the radar display while objects moving away from the radar get painted a red or orange color. The velocity can also be measured, so the brighter the color, the higher up the scale the winds go. Having a strong green/blue data point right next to a strong red/orange data point can indicate strong rotation in a thunderstorm. It may not mean that a tornado is happening though, as environmental data needs to be factored in.

A violent tornado struck the village of Oakfield at about 7:15pm CDT after it touched down 4 miles West-Northwest of the village. During its approach on Oakfield, it intensified to an F3 rating. When it tore through the village, it intensified further to an F4, but along its path 1 to 4 miles east of the village, it intensified to F5 strength. In this span, 4 homes were completely swept clean off their foundations and a couple automobiles became airborne missiles for a distance of about 400 feet. The core width of the most intense damage was about 150 to 200 yards, although at times, some secondary damage was observed in a 400 yard wide path.

Oakfield residents heard local sirens about 6-8 minutes before the tornado entered the village. Miraculously, no one was killed, but there were 12 injuries. Some of the injured were hospitalized. Along the tornado's path, 60 homes and 6 businesses were destroyed. An additional 130 homes and businesses were damaged. In Oakfield, a commercial canning company was devastated. Two churches in the village were also destroyed, as well as numerous vehicles. In the rural areas along the tornado's path, 18 barns and many sheds were destroyed or damaged and about 500 acres of crops were wiped out. Total damage amounts were $39.5 million in public/private property and $900,000 in crop loses. Residents reported that they had difficulty "popping" their ears as the tornado roared through their neighborhood.

Prior to entering Oakfield, the tornado hopped and skipped a few times and multiple vortices were observed at times during it's life cycle. Witnesses reported that the tornado "paused" for a minute or so on the southeast edge of Oakfield. As the tornado tore through Oakfield, it changed it's heading to east. Corn fields just east of Oakfield were reduced to short 1 to 4 inch high stubble and burn marks were clearly visible in the fields. In the third segment of the tornado's life, it turned northeast at a point 5.5 miles east of Oakfield and diminished rapidly. By the time it "roped out" 1 mile Northwest of Eden, it's supporting mesocyclone's location was 5 miles to the south! Debris was found east to the Lake Michigan shoreline and cancelled checks were later found 125 miles East-Southeast near Muskegon, Michigan.

There were many pictures taken of the Oakfield tornado, along with a few videos. Here's what we have available to us thanks to the following photographers: Cailyn Lloyd and Etta Held.

On October 1st, 2007, that National Weather Service (NWS) introduced Storm Based Warnings for tornadoes, severe thunderstorms, flash floods and marine hazards that are more geographically specific for these short-duration weather events. When issuing a warning, the NWS will specify areas within a county and refer to commonly known landmarks such as highways or rivers.

Back in 1996 when the NWS Milwaukee office issued a Tornado Warning for the Oakfield Tornado, the warning was "County Based", meaning that every location in the county was alerted to the tornado despite there being no threat to areas like Ripon, where the tornado had already passed. Now, only cities located within the 'polygon' will end up in the warning information. This adds more focus onto those communities that are in the path of the tornado and leaves out those that are not. 

Some warning devices such as Wireless Emergency Alerts, private sector and some TV station weather apps on phones and some county based Outdoor Warning Siren systems rely on these more focused warnings to guide whether they are alerted. Wireless Emergency Alerts rely on cell phone towers and their relative location to the warning to decide on whether a cell phone activates. Private sector and TV station cell phone applications (apps) rely on the device's location to geolocate where the user is in relation to the warning and whether to send a push notification on the warning.

In 2015, the National Weather Service made a change to the format of Tornado Warnings, Severe Thunderstorm Warnings and Flash Flood Warnings to better communicate threats to partners and constituents. This updated formatting is called Impact Based Warnings with the goal of this process to focus on providing more information to media and emergency managers, facilitating improved public response and decision making, and meeting societal needs in the most life-threatening weather events. 

The Impact Based Warnings will have "event tags" at the bottom of each severe thunderstorm, tornado and flash flood warning. The additional tornado event tags will have tornado threat information attached to them as a quick means to provide users and partners with potential high impact signals that prompt faster risk assessment and protective action. To show the difference in what the original Tornado Warning looked like from 1996 vs how it would look if it was issued today with the new Impact Based Warning formatting:

12 tornadoes in total occurred on this day, with the strongest being the Oakfield F5. The first tornado on the day occurred in northern Wisconsin in Lincoln County. The other 11 occurred in east central Wisconsin.

Thank you to the Oakfield Area Historical Society, Oakfield Public Library, Bob Riel, Doreen Conger, Peter Ochs and Owen Stoppleworth for this great archive of pictures that were collected from right after the tornado occurred. We tried to pin point where each picture was taken, but may be off on some of them since the damage was so bad that most of the houses or landmarks shown in the pictures were knocked down.