EF1 tornado in Isanti County, Minnesota

The tornado made contact just west of Day and traveled just north of a few houses, then hit a farm where multiples trees were uprooted or broken. A partially filled grain bin was also blown off its foundation. The tornado continued across open fields and wooded areas before dissipating. An anemometer on the southern edge of the tornado measured 87 mph.

During the evening of Friday, July 17th, a line of strong to severe thunderstorms that developed across northwest Minnesota, propagated south-southeast across central Minnesota and became a well defined bow echo segment. There were two areas that had the worst damage. One occurred in Stevens County where a swath of wind damage extended 3/4 of a mile to the southeast of Chokio, and about 1/4 of a mile wide. Many trees were snapped off just above the base, while others were uprooted. The second area was associated with straight-line winds, occasional downbursts, and two tornadoes that hit northern Isanti, and northern Chisago Counties.

There was ample instability and wind shear during the evening to hold supercell characteristics along this bow echo segment. As the storm bowed out to the southeast late in the evening, less instability and wind shear diminished the organized nature of the bow segment. However, a one bow echo segment allowed for two tornadic storms near Day and Rush City.

There was continued weakening of this bow echo overnight, with more individual line segments which caused brief, and isolated wind damage. Even local airport wind sensors, and private wind sensors were measuring wind gusts in the 40 to 50 mph range past midnight LST. The exception was in the Twin Cities metro area where the Flying Cloud airport measured a wind gust of 59 mph, and the Minneapolis/St. Paul airport measured a wind gust of 55 mph.