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User:Cyclonebiskit/Yellowstone

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Teton–Yellowstone tornado
F4 tornado
FormedJuly 21, 1987, 1:38 p.m. MST[1]
DissipatedJuly 21, 1987, 1:54 p.m. MST[1]
Highest winds
  • 207–260 mph (333–418 km/h)[2]
Max. rating1F4 tornado
FatalitiesNone
Damage$2.5 million (1987 USD)
Areas affectedTeton Wilderness and Yellowstone National Park, Wyoming
1Most severe tornado damage; see Fujita scale

On July 21, 1987, a violent tornado occurred across the Teton Wilderness and into Yellowstone, becoming both the westernmost and highest altitude tornado of such intensity on record in the United States.

Meteorological synopsis

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Teton–Yellowstone Tornado

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A map of all tornadoes in the United States from 1950–2019. The 1987 Yellowstone tornado is the westernmost F4 on record
Additional

The tornado traveled along a continuous 24.4 mi (39.2 km) during its 26 minute existence.[3] It had an average width of 2.5 km (1.6 mi) throughout this time, reaching a maximum width of 2.4 mi (3.9 km).[4] The tornado and associated microbursts devastated approximately 15,000 acres (6,100 hectares) of forest, uprooting an estimated 1 million trees.[5] A total of 72 microbursts accompanied the tornado, primarily along its eastern flank. These microbursts were enhanced by the local topography, with downdrafts from the parent thunderstorm being amplified within the many valleys of the area.[3] The Teton–Yellowstone tornado was the highest elevation violent tornado on record, with damage observed at a maximum elevation of 10,070 ft (3,070 m). However, other weaker tornadoes have occurred at higher elevations, with the record being observed at an approximate elevation of 12,070–12,240 ft (3,680–3,730 m) on July 4, 2004, in Sequoia National Park.[6][7] It is unknown whether or not a funnel cloud accompanied the tornado as the parent thunderstorm's cloud base is estimated to have been near the surface. Eye-witnesses near Enos Lake reported no funnel and a rapid onset of rain and hail with a roaring, train-like sound in the distance.[8]

The tornado touched down around 1:38 p.m. MST approximately 1.9 mi (3 km) northeast of Randolph Mountain in the Teton Wilderness. Traveling along a northeast trajectory at 55 mph (89 km/h), the tornado steadily intensified to F4 intensity within 3 minutes and widened as it approached Gravel Ridge before descending into the Pacific Creek Valley.[3] It reached its peak strength northeast of Gravel Ridge where a swath of F4 damage was assessed within a spin-up vortex approximately 660 ft (200 m) in diameter. Here, an estimated 2,700 Englemann spruces were uprooted, stripped of branches and leaves, debarked, and splattered with windblown topsoil. Fujita described this as some of the most severe tree damage documented within his career.[9] The tornado maintained this intensity for 7 minutes, traveling 6.2 mi (10 km) during this time.[10] After crossing Enos Lake (elevation 7,810 ft (2,380 m) MSL). Extensive tree damage occurred throughout the valley as the storm approached the steep slope of the Continental Divide.[3]

Moving up the steep slopes of the Continental Divide, the tornado weakened significantly. Damage was only classified as F0 or F1 along a 2.5 mi (4 km) path approaching the Divide. Tornado expert Ted Fujita hypothesized that the "tornado worked hard in maintaining its circulation" against the loss of angular momentum. The tornado was able to maintain an organized circulation due to energy pulses from the numerous microbursts which counteracted frictional forces.[10] The tornado reached an elevation of 10,070 ft (3,070 m) during its passage of the Divide.[3] Three large microbursts occurred within the eastern side of the tornado along the Continental ridge as downdrafts were enhanced by downslope flow.[11] Crossing several cliffs and valleys, the tornado later entered the Yellowstone River Valley. It gradually weakened as it traversed the relatively flat valley floor, eventually dissipating around 1:54 p.m. MST on the eastern slopes of the valley.[1][3]

The tornado was originally reported on as a large-scale blowdown event rather than a tornado. Fujita arranged a three-part survey of the damage area to determine the cause. The initial survey was conducted by air on July 30 – August 2, the second with stereo-pair photographs on August 19, and the third with another aerial survey and foot-based on August 27–30. These surveys revealed a 24 mi (39 km) long, 2.4 mi (3.9 km) wide swath of tree damage consistent with a tornado. Cyclonic patterns were found within an even broader area of wind damage caused by numerous microbursts.[5] The Teton–Yellowstone tornado is considered the best-documented high-elevation tornado on record.[7][12] Follow-up surveys of the damage were planned for 1988; however, destructive wildfires burned through large swaths of the greater Yellowstone area that year.[13] Firefighters conducted controlled burns of the damage swath to prevent the Mint Creek Fire from spreading to nearby ranches.[14] Damage to forests from the tornado remained visible along some trails in the Teton Wilderness in 2009.[15]

Other severe weather

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Two other tornadoes touched down in association with the parent storm system: an F2 north of Casper, Wyoming,[16] and an F1 north of Richfield, Idaho.[17] The former had no known reported damage according to the National Centers for Environmental Information.[16] The latter caused significant damage to crops and barns and killed 30 chickens.[17]

Severe thunderstorms across western Wyoming produced strong wind and hail, with the highest gust reaching 64 mph (103 km/h) at Hunt Field in Lander and hail up to 2.25 in (5.7 cm) in diameter in Teton Village.[18] Heavy rain over eastern parts of Yellowstone National Park led to flooding and mudslides, prompting road closures. Some roads were covered with up to 2 ft (0.61 m) of mud.[16] Lightning triggered multiple false burglary and fire alarms in Casper. Two small fires were also ignited by the lightning in Natrona County.[19] Scattered power outages occurred in Teton County.[20] Minor flooding affected structures across Jackson Hole.[21]

Utah

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References

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  1. ^ a b c Fujita 1989, p. 1933.
  2. ^ National Weather Service Forecast Office in Riverton, Wyoming [@nwsriverton] (July 21, 2019). "On this date, in 1987, an F4 Tornado tore through the Teton Wilderness and Yellowstone National Park , even crossing the Continental Divide, at 10,070 feet. An F4 Tornado has estimated winds of 207 to 260 mph and can do devastating damage. Here are some interesting facts. #wywx" (Tweet). Retrieved September 21, 2021 – via Twitter.
  3. ^ a b c d e f Fujita 1989, p. 1917.
  4. ^ Fujita 1989, p. 1916.
  5. ^ a b Fujita 1989, p. 1913.
  6. ^ Edwards, Roger (March 19, 2021). "The Online Tornado FAQ". Norman, Oklahoma: Storm Prediction Center. Retrieved September 26, 2021.
  7. ^ a b Monteverdi 2014, p. 3926.
  8. ^ Fujita 1989, p. 1926.
  9. ^ Fujita 1989, p. 1923.
  10. ^ a b Fujita 1989, p. 1925.
  11. ^ Fujita 1989, p. 1923–1924.
  12. ^ Dunn, Larry; Alder, William; McClung, Tim (June 21, 1994). The High Uinta Tornado (PDF) (Report). National Weather Service Forecast Office in Salt Lake City, Utah. p. 1. Retrieved September 26, 2021.
  13. ^ Fujita 1989, p. 1938.
  14. ^ Rothermel, Richard C.; Hartford, Roberta A.; Chase, Carolyn H. (January 1994). Fire Growth Maps for the 1988 Greater Yellowstone Area Fires (PDF) (Report). Ogden, Utah: United States Forest Service. p. 7. Retrieved September 25, 2021.
  15. ^ "Bridger-Teton National Forest Visitor Guide" (PDF). United States Forestry Service. 2009. p. 4. Retrieved September 26, 2021.
  16. ^ a b c Ziemianski 1987, p. 89.
  17. ^ a b Ziemianski 1987, p. 34.
  18. ^ Ziemianski 1987, p. 88–89.
  19. ^ "False alarms keep police, sheriff busy". Casper Star-Tribune. July 23, 1987. p. A3. Retrieved September 26, 2021 – via Newspapers.com. Free access icon
  20. ^ Conant, Lucy (July 22, 1987). "Summer storm batters area". The Jackson Hole Guide. p. A1. Retrieved September 26, 2021 – via Newspapers.com. Free access icon
  21. ^ Conant, Lucy (July 22, 1987). "Summer storm pounds valley". The Jackson Hole Guide. p. A22. Retrieved September 26, 2021 – via Newspapers.com. Free access icon

Further reading

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