June 17th, 2010 will certainly be a day that all residents in Minnesota will remember for some time. The day marks the highest number of tornadoes recorded in 24 hours, although a final total has not been recorded yet, it will surpass the previous record of 27 set in 1992. The fact that one EF-4 tornado was recorded was the first in the state since 2000 but by the end of the day 3 would be tallied, marking the highest one day total since the Black Sunday outbreak in 1967.
Most forecasters were well aware of the forthcoming storm system as models began hinting at the severe weather set-up days in advance . The biggest caveats in the forecasting of the event was whether or not morning convection would be able to clear out in time for sufficient heating to coincide with forecasted shear.
On the morning of the 17th an impressive cut-off low was situation over the eastern rockies with associated shortwaves helping to trigger the early morning elevated convection over the upper Midwest. The cut-off low not only was a staggering sight on the morning analysis charts but was clearly moving quickly and deepening, pointing a bullseye for a significant severe weather outbreak over the upper Midwest.
The surface chart was equally as impressive with a large surge of warm air into the northern plains in response to a retreating warm front through the region. Forcing was not going to be an issue with a sharp cold front situated to the west. In fact, questions remained if there would be too much forcing, creating a linear convective mode.
As the morning turned into afternoon it became very apparent that a significant severe weather event was indeed unfolding. The strong upper level support was continuing to shift eastward across the northern plains, and moisture advection throughout the warm sector had created a powder-keg environment.
Something to always keep in mind when forecasting or nowcasting severe weather, especially during June-Aug, is how strong the 700mb CAP is. A few years back Jon Davies wrote a great paper regarding how 700mb temperatures can hinder deep convection during the summer months in the northern plains. On June 17th, it didn’t appear that the cap was going to be a significant issue in northern Iowa into Minnesota and Wisconsin. But for future reference, here is a chart you can follow when forecasting in the future.
When afternoon convection started in earnest during the late afternoon hours it initially appeared to be linear in nature. But storms managed to stay discrete for several hours in advance of the cold front, allowing the storms to obtain supercellular structure. Here are just a few radar grabs from the storms as they evolved.
Here is a RUC sounding from Albert Lea, MN near the time of the on-going tornadoes.
Written by Ryan Wichman
*contributions from the NWS MPX
Freeborn County: EF4 Tornado Near Conger, Armstrong and Manchester
A storm damage survey team has determined an EF-4 tornado occurred in western Freeborn
County on Thursday June 17th. The following was determined from this survey and verified
reports, storm chaser video and photos, spotter information, combined with radar data.
Maximum Intensity: EF-4 with winds of 175 mph.
Track: First touched down 1 mile west-northwest of Mansfield and moved northeast to
approximately 3.5 miles west of Conger, where the tornado began to move more to the
east-northeast. West of Armstrong, the tornado then tracked nearly due north to just
west of Manchester, where it began to move to the north-northwest before dissipating
1.5 miles west of Hartland. Accounting for changes in direction, total path length was
approximately 20 miles, although the start and end points are 17 miles apart as the crow
Maximum Width: One mile.
Timing: Approximately 6:33 PM to 7:15 PM CDT.
At approximately 6:33 PM CDT, the tornado developed just north of 150th Street and about 1/3
mile east of the Faribault/Freeborn County line. The tornado moved to the northeast and grew
in width to approximately 250 yards. Near 80th Street and County Road 2, the tornado began
producing EF-2 damage. Crop damage became very evident with corn having several leaves
stripped. A homestead near this location was likely in the outer circulation of the tornado and
sustained some roof and siding damage. A nearby barn was destroyed to its brick foundation. A
car was also flipped over lengthwise at this location. Some evidence of tree debarking was
The tornado continued to the northeast and caused extensive crop damage approximately 500
yards in width. Near County Roads 17 and 63, the tornado grew to EF-3 intensity, and impacted
a farmstead and caused the complete destruction of three swine barns and the loss of 12 head
of swine. Two empty grain bins were completely blown away at this location. The house at this
location had some roof damage but appeared to be northwest of the main tornado path.
Approximately 100 feet northeast of the house, a 150 foot tripod style wind turbine tower was
twisted and toppled. This location also marked the beginning of crops being completely raked,
with only stalks of corn left and soybean fields being almost unrecognizable.
After passing through this farmstead, the tornado took a more east-northeast path across
County Road 63, and maintained EF-3 strength intensity. After passing County Road 63,
another farmstead was hit. At this location, two empty harvester silos were toppled.
The tornado continued to the northeast across County Road 4 where continued raking of the
fields was noted with significant deposition of debris along the tornado path. Numerous trees
were toppled at County Road 89 where it turns to the north. The tornado continued to the northnortheast,
grew to 1000 yards and strengthened to EF-4 Intensity, and impacted a farmstead
near the intersection of a local road and County Road 12 two miles north of Conger, around 650
PM CDT. The house at this location was completely destroyed as was the barn and several
other buildings. Extensive tree damage was noted with nearly all branches being removed from
Debarking of trees was widespread at this location. From this location, a car was tumbled a
distance of 3200 feet, and came to rest in a field east of County Road 12.
The tornado continued to the northeast across County Road 69 and County Road 46, where it
weakened slightly to EF-3 intensity. As it crossed County Road 46, a house was rotated off the
foundation. The tornado was approximately 700 yards wide at this point. To the north-northeast,
a swine barn was destroyed with sheet metal being carried off to Interstate 90. At this same
time, a satellite tornado developed and caused damage in the town of Armstrong.
The main tornado continued to the north northeast and was 500 yards in width. The tornado
crossed County Road 74 and caused EF-2 damage to three farmsteads. One farmstead with a
manufactured home was hit, and resulted in one fatality and one severe injury.
The tornado crossed Interstate 90 just west of County Road 14 as it grew to one third of a mile
in width and re-strengthened to EF-3 intensity. Several farmsteads saw significant damage
between Sugar Lake and County Road 14 with a house and two barns completely destroyed.
From this point the tornado continued to the north, and grew to one mile in width. Around 7 PM
CDT, a house and barn were destroyed approximately one mile west of Manchester on County
Road 25, where extensive tree and structural damage was also noted at several properties in
the area. Additionally, west of this tornadic damage, a separate area of tree and structural
damage was caused by strong thunderstorm winds associated with what is known as rear flank
About one mile north, the tornado weakened slightly to EF-2 intensity, where it damaged three
full grain bins near County Road 29. The tornado was approximately 1300 yards at this point.
Further north, at County Road 95, the tornado continued to weaken, although a farmstead still
received EF-1 damage to trees and structures.
Finally, the tornado continued north-northwest and began to narrow and weaken. The tornado
dissipated to the west of Hartland around 7:15 CDT.
Freeborn/Steele County: EF3 Tornado Near Clarks Grove to Ellendale
A storm damage survey team has determined an EF-3 tornado occurred in north central
Freeborn County and southwest Steele County on Thursday June 17th. The following was
determined from this survey, storm chaser photos and video, combined with radar data.
Maximum Intensity: EF-3 with winds 145 to 160 mph.
Reported Injuries: None.
Location: Touchdown was approximately two miles northwest of Albert Lea Airport, near
the intersection of Freeborn County Roads 14 and 20. It tracked to the north-northeast,
then moved into Steele County, where it began moving to the north-northwest, thereby
missing the city of Ellendale. A few miles later, it began moving toward the northwest,
and shortly before ending, it actually turned some more and moved toward the westnorthwest
until it finally dissipated.
Track: Accounting for the change in direction, the tornado had an actual path length of
18.8 miles, although the distance from start to end point is 16.8 miles as the crow flies.
Maximum Width: Approximately three-quarters of a mile.
Timing: Touchdown at 705 PM and dissipation was at 744 PM CDT.
Multiple farmsteads experienced significant structural and tree damage, including one house
completely destroyed and several others heavily damaged, many outbuildings destroyed,
dozens of trees uprooted and snapped with some debarked. Much of the first six miles of this
tornado path was EF-0 before it intensified rapidly.
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