Teton–Yellowstone tornado

The Teton–Yellowstone tornado was a rare high-altitude tornado which occurred on July 21, 1987, in the U.S. state of Wyoming.[1][2] Rated at F4 on the Fujita scale, it remains the strongest tornado ever recorded in the state and the only recorded F4/EF4 tornado in Wyoming history.[3][4] The tornado cut through a 39.2-kilometre (24.4 mi)-long and 2.5-kilometre (1.6 mi)-wide swath of the Teton Wilderness and Yellowstone National Park, crossing the Continental Divide.[1] Damage occurred at elevations ranging from 8,500 to 10,000 feet (2,600 to 3,000 m), making it the highest-altitude violent tornado recorded in the United States.[2] At the time, it was the highest-elevation tornado known,[5] since surpassed by several others, including a 2004 tornado above 12,000 feet in California's Sequoia National Park.[6] While no human fatalities or injuries occurred,[3] an estimated one million trees were felled by the tornado.[7] The tornado damage was originally thought to be the result of strong thunderstorm straight-line winds until the area was surveyed by University of Chicago severe weather meteorologist Ted Fujita and his colleagues, who published a paper in 1989 surveying the tornado's path and discussing its meteorological character.[1]

Teton–Yellowstone tornado
A large swath of trees leveled by the tornado
Meteorological history
DurationApprox. 26 minutes
FormedJuly 21, 1987 1:28 PM MST
DissipatedJuly 21, 1987 1:54 PM MST
F4 tornado
on the Fujita scale
Overall effects
CasualtiesNone
Damage$2.5 million (1987 USD)
Areas affectedTeton Wilderness, Yellowstone National Park
Part of the tornado outbreaks of 1987

Storm development and track

The tornado track began in a valley to the northeast of Mount Randolph,[1]: 1917  with the tornado's initial formation estimated by Fujita at 1:28 p.m. MST.[1]: 1933  The damage path became wider and more consistent as it approached Gravel Ridge, producing a large area of tree damage to the northeast of the ridge.[1]: 1917  The tornado appeared to intensify quickly, as the damage it produced increased from F0 intensity to F4 intensity in less than five kilometers, estimated at 3 minutes of travel time. The lone area of F4 damage was found north of Gravel Ridge,[1]: 1923  based on a small area affected by the worst tree damage: large Engelmann spruce trees between 30 and 40 centimetres (12 and 16 in) in diameter were found uprooted and stripped of their bark, with the bare trunks spattered with wind-blown topsoil.[1]: 1923  Meteorologist Ted Fujita noted that the only comparable forest damage he had seen associated with an F4 tornado had been in the Appalachian Mountains after the Murphy, North Carolina tornado of the 1974 Super Outbreak.[1]: 1923 

The tornado maintained F2-F3 intensity for the next 10 kilometers, producing a large swath of tree damage. During this period, it approached and crossed directly over Enos Lake in the Bridger–Teton National Forest.[1]: 1917  A group of nine campers near Enos Lake reported that they saw no funnel cloud, but that the storm developed quickly and a "roar like a train in the distance" was accompanied by hailstones the size of golf balls. Fujita hypothesized that because of the area's high elevation and the storm's low cloud base, no funnel cloud would have been visible.[1]: 1926  The tornado then descended into Pacific Creek Valley before climbing up to a high plateau at nearly 3,000 meters in elevation, weakening significantly. It produced more tree damage on steep slopes until it crossed the Continental Divide, damaging trees at an elevation of 10,070 feet. More severe tree damage occurred in several cirques. The tornado then crossed the drainage of Falcon Creek before descending into the Yellowstone River Valley, gradually weakening as it did so. The damage path became more sporadic until it disappeared on the valley's far eastern side,[1]: 1917  with the tornado's time of dissipation calculated to have been 1:54 p.m. MST.[1]: 1933 

Summary

The tornado's total damage path was 39.2 kilometres (24.4 mi) long, with an average width of 2.5 kilometres (1.6 mi) and a maximum width of 3.9 kilometres (2.4 mi).[1]: 1916–1917  Fujita estimated the tornado's duration on the ground at approximately 26 minutes,[1]: 1938  with a forward velocity of 90 kilometres per hour (56 mph).[1]: 1917 

Aftermath

No casualties resulted from the tornado, though as many as twelve people were trapped in the backcountry by the storm. Trail maintenance crews and other federal workers labored for weeks to clear approximately 15 miles of trail blocked by the downed trees,[5] and the total cost of the damage was recorded as $2.5 million.[3]

Discovery and study

After the July 23 report of a massive blowdown in the Teton Wilderness by the Forest Service, Fujita arranged for multiple aerial surveys by Cessna aircraft of the tornado's track, resulting in more than 1,400 photographs that recorded every single damaged tree. The southernmost area of the track was also visited on foot and photographed by Fujita's colleague Bradley S. Churchill.[1]

Timber blowdown

In the fall of 1987, U.S. senator for Wyoming Malcolm Wallop, the Fremont County Commission, and timber groups lobbied for the ability to harvest the fallen timber from the tornado's path, arguing that it posed a threat because of wildfire and beetle infestation risks and would provide nearby lumber mills with work. The Wyoming Chapter of the Sierra Club opposed the suggestion on the grounds that the harvesting would require many miles of logging roads through wilderness and would create a dangerous precedent.[8] In the end, much of the area burned in the Huck Snake River Complex and Mink Creek fires during the Yellowstone fires of 1988, though several thousand acres of the tornado blowdown track remained unaffected.[9] This prevented Fujita and his colleagues from returning to perform follow-up aerial photographic surveys and site visits.[1]: 1938–1939 

References
  1. Fujita, T. Theodore (September 1, 1989). "The Teton-Yellowstone Tornado of 21 July 1987". Monthly Weather Review. 117 (9): 1913–1940. Bibcode:1989MWRv..117.1913F. doi:10.1175/1520-0493(1989)117<1913:TTYTOJ>2.0.CO;2. ISSN 1520-0493 – via American Meteorological Society.
  2. Edwards, Roger (January 29, 2009). "The Online Tornado FAQ". National Weather Service. Retrieved December 21, 2009.
  3. "Wyoming Climate Atlas". Water Resources Data System & State Climate Office. Wyoming State Climate Office. Archived from the original on October 19, 2022. Retrieved December 21, 2009.
  4. "Tornado History Project: Maps and Statistics". Archived from the original on January 17, 2018. Retrieved January 7, 2014.
  5. Thuermer Jr., Angus M. (August 5, 1987). "Storm was world-record tornado". Jackson Hole News. pp. 1, 12. Retrieved January 30, 2023 – via Newspapers.com.
  6. Monteverdi, John P.; Edwards, Roger; Stumpf, Gregory J. (November 1, 2014). "An Analysis of the 7 July 2004 Rockwell Pass, California, Tornado: Highest-Elevation Tornado Documented in the United States". Monthly Weather Review. 142 (11): 3925–3943. Bibcode:2014MWRv..142.3925M. doi:10.1175/MWR-D-14-00222.1. ISSN 1520-0493. S2CID 120568073.
  7. "Tornado Information". National Weather Service Weather Forecast Office, Riverton, WY. NOAA. Archived from the original on October 4, 2006. Retrieved December 21, 2009.
  8. "The Wyoming chapter of the Sierra Club says it..." United Press International. September 1, 1987. Retrieved January 30, 2023.
  9. Greater Yellowstone Coordinating Committee (January 25, 1989). "The Greater Yellowstone Fires of 1988: Questions and Answers" (PDF). NPS History Electronic Library & Archive. Archived (PDF) from the original on December 24, 2022. Retrieved January 30, 2023.

44.02°N 110.23°W / 44.02; -110.23

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