Heat and Monsoonal Conditions This Week

Dangerous heat will build across portions of the West through this week where new daily record highs are forecast. Monsoonal showers and thunderstorms may result in flash flooding and debris flows for portions of Southwest into the Four Corners and central Rockies through at least the midweek. Stationary frontal boundary across the South and Southeast will focus showers and thunderstorms. Read More >

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Overview

On Wednesday, June 19, 2019 a thunderstorm began to develop on the border of Park and Big Horn counties around 5 PM. As this storm moved east it strengthened and reached its peak intensity in extreme southeastern Big Horn County. The storm crossed into Johnson County and produced a tornado on Powder River Pass in the Bighorn Mountains just before 7 PM. Considerable tree damage occurred along and near US Highway 16 as the tornado moved east along its 3.7 mile path. Hundreds of conifer trees were uprooted or snapped at their trunks. Additionally, several large wooden snow fences were torn apart, with fencing debris thrown in all directions. This tornado was unusual in that it occurred at a high elevation of just under 10,000 ft along its western path.

The damage produced by this storm was consistent with an EF-1 tornado, with estimated peak winds of 110 mph. The time of the tornado was estimated by comparing the location of the damage with radar imagery.

A destroyed snow fence on the north side of US Highway 16

Tornado
Photos

Tornadoes:

Tornado - Powder River Pass
Johnson County, Wyoming

Date	Wednesday, June 19, 2019
Time (Local)	6:56 - 7:02 PM MDT
EF Rating	EF - 1
Est. Peak Winds	110 MPH
Path Length	3.7 miles
Max Width	250 yards
Injuries/Deaths	0
Summary: A tornado developed near Powder River Pass (elevation 9,700') between Ten Sleep and Buffalo, causing considerable tree and snow fence damage along and near US Highway 16. At its widest the tornado caused sporadic damage 250 yards across.

Track Map


Location of the track between Ten Sleep and Buffalo	Zoomed in track with topographic map	6:58 PM radar reflectivity (0.5 degree) from KRIW	6:58 PM radar base velocity (0.5 degree) from KRIW

The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:

EF0 Weak 65-85 mph	EF1 Moderate 86-110 mph	EF2 Significant 111-135 mph	EF3 Severe 136-165 mph	EF4 Extreme 166-200 mph	EF5 Catastrophic 200+ mph

Photos


Snapped and uprooted trees on the south side of US Highway 16 (NWS Survey)	Damaged trees along Forest Road 448 south of US Highway 16 (NWS Survey)	Damaged trees south of US Highway 16 (NWS Survey)	Snapped and delimbed trees south of US Highway 16 (NWS Survey)


Snapped and uprooted trees on the south side of US Highway 16 (NWS Survey)	Rebar from snow fencing was tossed and stuck into the ground on the north side of US Highway 16 (NWS Survey)	Snow fencing debris was tossed and stuck into the ground on the north side of US Highway 16 (NWS Survey)	Damaged snow fence on the south side of US Highway 16 on Powder River Pass (NWS Survey)


Destroyed snow fence on the south side of US Highway 16 on Powder River Pass (NWS Survey)	Damaged snow fence on the north side of US Highway 16 on Powder River Pass (Johnson County Planner)	Bent rebar anchoring a snow fence on the south side of US Highway 16 on Powder River Pass (NWS Survey)	Snow fencing debris was tossed and stuck into the ground on the north side of US Highway 16 (NWS Survey)