On Friday evening, September 19, 2014 a supercell thunderstorm developed in southern Manitoba and then moved southeasterly across Pembina County in North Dakota then crossed the Red River into northwestern Minnesota. It intensified quickly and a Tornado Warning was issued almost immediately as it crossed the international border. If you look carefully at the animation below you can probably detect the classic “hook echo” from the cell. It appears no tornado actually formed until it crossed into northwestern Minnesota.
As the supercell (rotating thunderstorm) was moving across Kittson County a tornado did form and was moving to the ESE. The tornado with a path width of approximately 300 yards moved across Kittson County into Roseau County.
As it moved into Roseau County it approached our Greenbush, North Dakota Agricultural Weather Network (NDAWN) site which is located 7 miles west of Greenbush. According to information supplied by the National Weather Service Office (NWS) in Grand Forks, North Dakota, the NDAWN station there was likely on the edge of the swirl from the tornado. The station recorded a top wind speed of 93 miles per hour as the tornado moved by the station. The peak gust was recorded at 7:28 PM CDT which is near the estimated time given by the NWS in the storm report presented below.
The NWS in Grand Forks took a picture of the station as they were doing a ground survey of the event on Saturday morning. The station appears to have survived unscathed by the tornado. Unfortunately, other structures were not so lucky. The farmstead in the picture below, although the trees looked to have survived very well, had damage to two big grain bins and lost steel roofing and doors off of a couple of pole sheds. There were other reports of damage as well across northwestern Minnesota.
Below is a base velocity image from the Mayville (MVX) Dopper radar at nearly the same time our Greenbush station recorded the maximum wind gust of 93 mph. Greenbush is located in far west central Roseau County pretty much right where the maximum outflow/inflow zone can be observed in the image below.
That 93 MPH wind gust was the highest wind speed recorded at any NDAWN station since the network was established 25 years ago. It currently consists of 75 stations. Previous to Friday’s event, the highest NDAWN wind speed was at the Linton, ND station on August 3, 1996 when the wind gusted to 88 mph in a severe thunderstorm near midnight that evening.
Besides a tornado, strong damaging “straight line” wind, the super cell also dropped some very large hail, some as larger than golf balls. Although the image below doesn’t quite reach that status, there were reports of much larger stones.
The storm did some major damage and although such damage can not be eliminated, weather stations in combination with Doppler radar images, trained professionals at the NWS and surface reports from trained storm spotters all are very useful tools in the protection of human lives.
Daryl Ritchison