June 22 2013 Banner County Tornado Rated EF1

Banner County EF1 Tornado

June 22, 2013

 

An intense thunderstorm affected northwestern Banner County, Nebraska, during the late afternoon on Saturday, 22 June 2013.  The storm was classified as an HP, or high precipitation supercell which produced torrential rain along with very large and damaging hail.  In addition to the rain and baseball sized hail, Doppler radar indicated very strong rotation within the storm which was capable of producing a tornado.  The National Weather Service in Cheyenne issued a Tornado Warning at 4:44 PM MDT which included northwestern Banner County.  A tornado was reported by an off duty National Weather Service employee at 4:51 PM about 9 miles east of La Grange, Wyoming.  This tornado was very difficult to see, as it was likely obscured by the heavy rains associated with the HP supercell. 

 

The image shown below is from the Cheyenne, Wyoming Doppler radar shortly after 5:00 PM MDT on 22 June 2013.  The left hand side of the image shows the reflectivity, which indicates the intensity of rain and possible hail within the storm.  Most notably, there is the distinct presence of a “hook echo,” or radar pattern resembling a fish hook.  This is caused by air rushing into the storm and wrapping into the mesocyclone (rotating updraft), resulting in a hook-shaped appearance to the precipitation field.  Storm relative winds are seen on the right side of the image.  Green colors indicate motion toward the radar, while reds indicate motion away from the radar.  Meteorologists look for these colors to be side-by-side as an indication for sufficient rotation for tornado development, especially when they are indicative of higher values (brighter colors).

 

 

 

 

Unfortunately, the tornado did cause some property damage.  A storm survey team from the National Weather Service in Cheyenne traveled to northwest Banner county to determine if the damage as caused by a tornado, and if so, the path and intensity of the tornado.  They were able to confirm that an EF1 tornado, with maximum wind gusts to 100 MPH, occurred between 4:50 PM and 5:05 PM on 22 June 2013.  The path length was estimated to be 7.8 miles, from 17 miles west-northwest of Harrisburg, Nebraska, to 10 miles northwest of Harrisburg.  The width of the tornado was estimated to about 100 yards.  A total of 8 structures were damaged with at least 1 outbuilding destroyed.  The outbuilding was supported by large wooden planks at least 6 inches thick with a majority of those snapped at the center.  The roof was mostly removed from a 3 stall garage, but the walls remained intact.  A two story residence was damaged by flying debris, with a 2 by 4 driven through the second floor wall by the tornado.  Sheet metal and wooden boards from damaged outbuildings were found 50 to 100 yards to the northwest in a shelterbelt.  6 power poles were snapped near the touchdown point, with another damaged east of Stegall road.  Several 6 to 12 inch diameter hardwood trees were also snapped, and center pivots were either flipped or twisted in multiple directions along the path of the tornado.

 

Surveyed damage path of the EF1 tornado northwest of Harrisburg on 22 June 2013.

 

An HP supercell in northwest Banner county on 22 June 2013.  Torrential rain associated with these storms can make it very difficult or impossible to spot what would be referred to as a rain-wrapped tornado.  The greenish hue to the precipitation shield is an indication of possible very large hail.  Photo courtesy of Becca Mazur.

 

Tree trunk twisted and snapped.

 

Large tree branches snapped.

 

2 by 4 driven through second floor wall by tornadic winds. Almost any object can become a potentially deadly missile in a tornado.

 

3 stall garage heavily damaged by tornado.

 

Snapped wooden post from destroyed outbuilding.

 

Wooden post thrown into metal wall.

 

Single power pole snapped at bottom.



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