NOAA's National Weather Service Weather Forecast Office

   The evening of June 14th saw a rash of severe weather across central Minnesota, as a powerful squall line raced down I-94 through western Minnesota and into the Twin Cities.  Trained spotters and law enforcement agencies provided many valuable reports of hail as large as nickels, measured wind speeds as high as 65 mph, and downed trees, tree limbs, and structural damage from the high winds. 

    However, those are not the only reports received at the NWS in Chanhassen on that Saturday evening.  There were also many independent reports of tornadoes, as the line of storms swept southeastward across central Minnesota.  The first reports came from the Alexandria and Long Prairie vicinities, with the emergency dispatch centers from Douglas, Pope, and Todd counties calling to notify us of reported tornadoes in their respective counties.  Not long after these reports were received, calls began pouring in from Kandiyohi, Meeker, and Stearns counties, including a report near New London, where two law enforcement officers and two trained spotters independently reported a tornado.

   As these calls flooded the NWS office, the meteorologists watching and warning for the storms were a bit surprised.  The radar data showed no rotation conducive to even a small tornado spin-up, and the very dry atmosphere made the environment unfavorable for tornado development.  As the reports were coming into the office, personnel concluded that these were likely "gustnadoes" on the gust front boundary emanating from the squall line, and these thoughts were relayed to the various law enforcement agencies and other spotters in the area.  Photos and video of several of these tornado reports have been received and reviewed, confirming the initial thoughts that these were harmless "gustnadoes".

   Some of you may be asking...  What is a gustnado?  Is it a tornado?  Is it dangerous?

   A gustnado is a rotating column of air that forms as a result of turbulence along a thunderstorm gust front boundary.  Gustnadoes are associated with shelf clouds, a cloud structure that is often confused with a wall cloud, which is sometimes a tornadic cloud feature.  A gustnado is not a tornado, and it is not typically dangerous.

   On that Saturday evening, the gust front boundary was clearly evident in radar data from the Chanhassen Doppler radar, and often, many of the reports occurred several miles ahead of the main area of precipitation with the squall line, which is where the gust front was located.  As the shelf cloud associated with the squall line moved over the NWS office in Chanhassen, meteorologists observed the turbulence within it, seeing how it could be confused with a more dangerous wall cloud feature and consequently, result in the volume of tornado reports.

   We very much appreciate all of the valuable reports from the volunteers that we receive during active weather in Minnesota and Wisconsin, and we would like to thank you all for the service that you provide for us and the safety of the communities you live in.