Posted at 5:45 PM on June 16, 2011
by Paul Huttner
Filed under: Tornadoes
It's been a year Friday since the biggest tornado outbreak in Minnesota history.
It was one of the most memorable days in Minnesota weather history. It also ranks up there as one of the biggest events for my broadcasting career with the Halloween Mega Storm in 1991, the Chicago heat wave in 1995, Monsoon storms and wildfires in Arizona, and last year's Domebuster in December.
I have written extensively about the events of last year's "Minnesota Super Outbreak" , but I think our local NWS has done an amazing job this year of revisiting the events of last June 17th. The complete report is here, but here are some highlights.
74 tornadoes across four states, including 48 in Minnesota. The number of Minnesota tornadoes was a new state record for tornadoes in a day.
16 strong to violent tornadoes (rated EF2 or higher), with 11 of those in Minnesota.
The three EF4 tornadoes in Minnesota were the first in the state since the Granite Falls F4 of July 25, 2000.
In terms of number of tornadoes, this outbreak was the 2nd largest on record in meteorological summer (June to August) at the time it occurred.
NWS offices in the Northern Plains began to advertise the potential for severe weather 5 days in advance of this tornado outbreak in the Hazardous Weather Outlook products.
The Storm Prediction Center issued Tornado Watches with a combined average lead time of 4 hours and 24 minutes for the tornadoes.
87 Tornado Warnings, 83 Severe Thunderstorm Warnings, and 3 Flash Flood Warnings were issued by National Weather Service offices in this region over approximately a 12 hour period. 279 follow-up statements to those warnings were also issued.
The average lead time for Tornado Warnings during this outbreak was slightly over 19 minutes.
Here's another way to look at the mayhem from June 17th.
Rotation Track Maps
"The National Severe Storms Laboratory produces several experimental products that prove useful when analyzing severe weather outbreaks. One of those is something called a "rotation track map". This map is produced by running radar velocity data through a filter, and determining the shear at given instants in time across the entire United States radar network. These instantaneous values are then integrated across an entire time period. The resulting maps can reveal both tracks of rotating supercells, and fluctuations in intensity in those supercells.
An example of one of those maps is shown below, for June 17, 2010."
There is slight risk for a few severe storms on the anniversary Friday, but nothing like what we saw a year ago that made weather history in Minnesota.