Associated Press

Utah is not a place known for tornadoes, but 15 years ago, on Aug. 11, 1999, a tornado ripped through downtown Salt Lake City.

Mike Leavitt, the governor of Utah at the time of the tornado, spoke to reporters just outside the Delta Center after the tornado and, according to the Deseret News, said, "Standing here in the calm of an August afternoon, it's almost inconceivable what happened.”

The following are 15 facts about the Salt Lake tornado — and Utah tornadic activity in general — for the 15th anniversary of the event.

Related: 15 years later, Utahns remember tornado that ripped through downtown Salt Lake City

The Salt Lake tornado was a category F2 storm
National Weather Service Forecast Office Salt Lake City

Tornadoes are ranked using the Enhanced Fujita scale. A category F0 tornado, the lowest category, has wind speeds of 65-85 mph, while the highest category, an F5, has wind speeds over 200 mph, according to the National Weather Service. The Salt Lake tornado became an F2 tornado, with wind speeds between 111 and 135 mph, just before entering the downtown district of Salt Lake City.

>> The Salt Lake tornado rips through downtown Salt Lake City on August 11, 1999.

The Salt Lake tornado was the most destructive in Utah’s history
National Weather Service Forecast Office Salt Lake City

The Salt Lake tornado caused an estimated $170 million in damage. The Delta Center’s roof was damaged and one of the tents set up for the Outdoor Retailers Convention was destroyed. The Wyndham (now Radisson) Hotel had windows blown out and closed temporarily to clean up the debris and shards of glass that had fallen to the ground. The Conference Center of The Church of Jesus Christ of Latter-day Saints, under construction at the time, was partially damaged when a crane toppled. Many homes were damaged, with 34 left uninhabitable, and 500 trees were destroyed and 300 were significantly damaged, according to the National Weather Service.

>> The Salt Lake tornado in downtown Salt Lake City (the orange fireball is a power substation exploding).

The Salt Lake tornado caused the second tornado-related fatality on record in Utah
Crandy family

Allen Crandy of Las Vegas, a contractor at the Outdoor Retailers Convention, was killed when flying debris hit him in the head. Crandy, who was 38 and a father of three, died on his 13th wedding anniversary, according to an article in the Los Angeles Times. One hundred and fifteen years earlier, on July 6, 1884, a 7-year-old girl, Kitty Wells, was killed when a tornado struck along the Weber River about 23 miles from Wanship, according to an account in the Deseret News that was quoted on the National Weather Service of Salt Lake City’s website. Wells and Crandy are the only people known to have died from a tornado in Utah.

The Salt Lake tornado led to the temporary closing of Salt Lake City
Gary McKellar, Deseret News archives

During the night of Aug. 11, 1999, Salt Lake City was closed to everyone but emergency crews, according to the article published in the Deseret News. These emergency crews included those who worked to restore electricity to parts of the city as well as workers who removed glass from the walkways and trees, some of which had landed on cars and others that blocked major roadways. Sections of two streets in Salt Lake remained closed days after the tornado for the cleanup of the tents at the Outdoor Retailers Show as well as because of the danger of the collapsed crane at the Conference Center construction site, according to an article in the L.A. Times.

The Salt Lake tornado caused more than 80 injuries
Gary McKellar, Deseret News archives

The Deseret News reported that 81 people were transported to area hospitals as a result of the tornado, with 16 people still in the hospital the next day. Three of the injured were listed in critical condition and one 43-year-old woman was listed as critically injured.

Tornadoes in Utah are rare
Julie Dockstader

To state the obvious, Utah has “one of the lowest incidences of tornadoes in the nation,” according to the National Weather Service of Salt Lake City. Utah averages two tornadoes per year, with a category F2 or stronger tornado only forming on average once every seven years. In contrast, USA Today reports that the 30-year average number of tornadoes per year in Oklahoma is more than 50. In addition, the highest wind speed of a tornado ever recorded occurred in Oklahoma on May 3, 1999 — just a few months before the Salt Lake tornado. University of Oklahoma scientists recorded that tornado’s wind speed at 318 mph, which was only one mile per hour short of becoming an F6 tornado on the old Fujita scale, according to USA Today.

Salt Lake City is not the only major city to be hit by a tornado
Associated Press

A tornado striking the central business district of a major city is rare, but it has happened. The first recorded tornado in a major city was categorized as an F3 and occurred in St. Louis, Missouri, according to a list compiled by Roger Edwards and Joe Schaefer of the Storm Prevention Center. Nine people died in that storm, but St. Louis saw an even deadlier tornado on May 27, 1896, when 255 people died, making it the deadliest tornado in a major city. The last major city with a tornado was Springfield, Massachusetts, on June 1, 2011, according to the list by Edwards and Schaefer. Some of the other major cities that have had tornadoes include Dallas, Texas; Houston, Texas; Indianapolis, Indiana; Miami, Florida; Atlanta, Georgia, and Minneapolis, Minnesota.

>> Children stand in the street near Eighth and Rutger in St. Louis after it was hit by a tornado on May 27, 1896.

The majority of tornadoes that form in Utah occur between May and September
Deseret News archives

There have been 129 tornadoes in Utah since 1950, according to the National Weather Service of Salt Lake City. Of those 129 tornadoes, 111 have occurred during the months between May and September, with the times between 11 a.m. and 5 p.m. as the most frequent for tornado activity, according to the National Weather Service of Salt Lake City.

>> A tornado moves through the town of Manti, Utah, Sunday, Sept. 8, 2002.

Utah’s strongest tornado occurred exactly six years before the Salt Lake tornado
Desert News archives

At about 6:50 p.m. on Aug. 11, 1993, a category F3 tornado, with winds between 136 and 165 mph, touched down near Chepeta Lake, roughly 25 miles north of Roosevelt in the Ashley National Forest of the Uinta Mountains, according to the National Weather Service of Salt Lake City. The tornado actually touched down three times and was the highest mountain tornado recorded in Utah. The tornado uprooted hundreds of trees in a 1,020-acre area and, on its third touchdown, damaged four vehicles belonging to a Scout troop that was camping in the area, according to the National Weather Service of Salt Lake City. None of the 125 people in the group were hurt.

>> Manti tornado, 2002

Only two tornadoes since the Salt Lake tornado have been higher than F0
Deseret News archives

Of the 34 recorded tornadoes that have occurred in Utah since Aug. 11, 1999, only two were higher than F0. The first was less than a month after the Salt Lake tornado in Naples, in Uintah County. The tornado formed at about 3:30 p.m. on Sep. 3, 1999, and was categorized as an F1 with wind speeds of 86-110 mph. It injured one woman and caused roughly $100,000 in damage, according to the National Weather Service of Salt Lake City.

The second tornado was categorized as an F2 on the old scale but would be considered an F3 today, with winds estimated to be 157 mph, according to the National Weather Service of Salt Lake City. It formed in Manti on Sept. 8, 2002. The tornado caused widespread damage, including lifting a semitrailer loaded with insulation 35-40 feet away onto its side and throwing a wood shed 200-300 feet away across Highway 89. The tornado caused an estimated $2 million in damage, making it the most destructive tornado other than the Salt Lake tornado since 1950.

>> Aftermath of the Manti tornado, 2002

Utah’s first recorded tornado occurred over water
Associated Press

The first recorded tornadic activity in Utah was described as a “funnel-shaped waterspout” that occurred on Aug. 19, 1869, according to the National Weather Service of Salt Lake City. The waterspout, a term used for a tornado that forms over water, formed over the American Fork River and washed out seven bridges and caused $1,500 in damage to roads along the river, according to the National Weather Service of Salt Lake City.

>> Small boats are dwarfed by a waterspout off Key West, Fla., June 21,1975.

The majority of waterspouts in Utah occur over the Great Salt Lake
Ravell Call, Deseret News

Since 1950, 22 waterspouts have been recorded in only three bodies of water in Utah. The Great Salt Lake has had 12 confirmed waterspouts, the most in Utah, while Utah Lake has recorded four and Bear Lake has recorded six, according to the National Weather Service of Salt Lake City.

>> A view from above Antelope Island of the Great Salt Lake, Monday, Dec. 23, 2013.

September is the most likely month for a waterspout to form in Utah
Scott G Winterton, Deseret News

Of the 22 waterspouts that have formed in Utah since 1950, nine of them were recorded in September, according to the National Weather Service of Salt Lake City. No waterspouts have formed in Utah during January through April and in December. The most likely times for waterspouts to form is at 8 a.m. or 5 p.m., both of which have four recorded instances. In addition, both 1996 and 1998 had four instances of waterspouts forming, the most since 1950, according to the National Weather Service of Salt Lake City.

>> Boaters enjoy the day on the Great Salt Lake Sunday, April 21, 2013.

Waterspouts, while less destructive than tornadoes, have still caused damage in Utah
Jason Olson, Deseret News archives

Being that waterspouts are formed over water, they generally do not cause a lot of damage. However, on Sept. 13, 1982, a waterspout over Utah Lake moved onto land near the Provo Airport and damaged a security gate and flipped a plane on its back even though the plane had been tied down at the time, according to the National Weather Service of Salt Lake City. On May 26, 1998, a waterspout over Bear Lake caused a boat on a trailer in the parking lot of the Bear Lake State Headquarters to tip over. In the marina, some sailboats floated free when high wind speeds snapped their mooring lines, according to the National Weather Service of Salt Lake City.

>> Kite boarders take advantage of a slight breeze blowing over Lincoln Beach on the south end of Utah Lake Wednesday, July 9, 2008.

There has not been a recorded waterspout in Utah since 1998
Jeffrey D. Allred, Deseret News

The last recorded waterspout to form in Utah occurred at Bear Lake on Oct. 4, 1998, at about 1 p.m., according to the National Weather Service of Salt Lake City. The waterspout only lasted about three minutes before dissipating. Since that time, 36 tornadoes have been recorded in Utah, according to the National Weather Service of Salt Lake City.

>> A family plays on the beach of Bear Lake in Bear Lake County, Utah, Friday, June 18, 2010.