User:Cyclonebiskit/Yellowstone

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.

Teton–Yellowstone Tornado

 * Utilizing Normalized Anomalies to Assess Synoptic-Scale Weather Events in the Western United States Weather and Forecasting
 * July 21, 1987 SPC map
 * damage pic?


 * Additional
 * Estimating Enhanced Fujita Scale Levels Based on Forest Damage Severity

The tornado traveled along a continuous 39.2 km during its 26 minute existence. It had an average width of 2.5 km throughout this time, reaching a maximum width of 3.9 km. The tornado and associated microbursts devastated approximately 15000 acre of forest, uprooting an estimated 1 million trees. 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. The Teton–Yellowstone tornado was the highest elevation violent tornado on record, with damage observed at a maximum elevation of 3070 m. However, other weaker tornadoes have occurred at higher elevations, with the record being observed at an approximate elevation of 3680 – on July 4, 2004, in Sequoia National Park. 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.

The tornado touched down around 1:38 p.m. MST approximately 3 km northeast of Randolph Mountain in the Teton Wilderness. Traveling along a northeast trajectory at 55 mph, the tornado steadily intensified to F4 intensity within 3 minutes and widened as it approached Gravel Ridge before descending into the Pacific Creek Valley. It reached its peak strength northeast of Gravel Ridge where a swath of F4 damage was assessed within a spin-up vortex approximately 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. The tornado maintained this intensity for 7 minutes, traveling 10 km during this time. After crossing Enos Lake (elevation 2380 m MSL). Extensive tree damage occurred throughout the valley as the storm approached the steep slope of the Continental Divide.

Moving up the steep slopes of the Continental Divide, the tornado weakened significantly. Damage was only classified as F0 or F1 along a 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. The tornado reached an elevation of 3070 m during its passage of the Divide. Three large microbursts occurred within the eastern side of the tornado along the Continental ridge as downdrafts were enhanced by downslope flow. 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.

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 39 km long, 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. The Teton–Yellowstone tornado is considered the best-documented high-elevation tornado on record. Follow-up surveys of the damage were planned for 1988; however, destructive wildfires burned through large swaths of the greater Yellowstone area that year. Firefighters conducted controlled burns of the damage swath to prevent the Mint Creek Fire from spreading to nearby ranches. Damage to forests from the tornado remained visible along some trails in the Teton Wilderness in 2009.

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

Severe thunderstorms across western Wyoming produced strong wind and hail, with the highest gust reaching 64 mph at Hunt Field in Lander and hail up to 2.25 in in diameter in Teton Village. 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 of mud. Lightning triggered multiple false burglary and fire alarms in Casper. Two small fires were also ignited by the lightning in Natrona County. Scattered power outages occurred in Teton County. Minor flooding affected structures across Jackson Hole.


 * Teton timber blowdown traps 9 packers Casper Star-Tribune
 * 15,000-acre B-T blowdown being mapped Casper Star-Tribune
 * Tornado blamed for timber blowdown The Billings Gazette
 * Blowdown debate heats up as wilderness harvest is eyed Jackson Hole News

Utah

 * Major Storm Drenches Utah South Idaho Press
 * Insurance claims mount after storm The Times News
 * All hail breaks loose in Utah County The Daily Herald
 * Storm The Daily Herald (continued)
 * Storm sends several to emergency facilities The Daily Herald
 * Hailstorm Sours an Already Depressed Tart-Cherry Industry The Salt Lake Tribune
 * Floods at State Offices Leads to Soggy Day Off for Workers The Salt Lake Tribune
 * Summer Torrent Proves to Be Too Much, Too Fast The Salt Lake Tribune
 * Summer Torrent Proves to Be Too Much, Too Fast The Salt Lake Tribune (continued)
 * Heavy Storm Brings Relief to Valley Tooele Transcript-Bulletin
 * Hailstorm claims total $7.4 million in county The Daily Herald
 * Damage The Daily Herald (continued)
 * Farmers try to recover from devastating July hailstorm The Daily Herald
 * Crops The Daily Herald (continuued)
 * State will assess local storm damage The Payson Chronicle