A cold front and associated shortwave moved across northern Wyoming during the evening of Sunday, August 8. Strong mid-level winds mixed to the surface and produced high winds in northern Wyoming.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS RIW wrote it up.
A cold front and associated shortwave moved across northern Wyoming during the evening of Sunday, August 8. Strong mid-level winds mixed to the surface and produced high winds in northern Wyoming. The strongest recorded wind speed was northeast of Buffalo where a gust of 73 mph was reported. Wind gusts of greater than 58 mph were also reported in northern Big Horn and Park counties.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Riverton, WY wrote its last area forecast discussion before the first event at Aug 8, 4:34 PM MST, 2 hours 5 minutes earlier.
Area Forecast Discussion National Weather Service Riverton WY 534 PM MDT Sun Aug 8 2021 .SHORT TERM...This afternoon through Monday night Clear skies and dry conditions and not as smoky this morning. This will change later today, as a cold front approaches the Cowboy State. Smoke will infiltrate back into western portions this morning, spreading across the forecast area through the day. This may be temporary, as models indicate clearing conditions behind the front tonight and Monday. Winds will also increase across western and southern portions this afternoon, as the gradient tightens in response to the approaching front. Critical fire weather conditions will result across the south, as winds gust up to 35 mph and relative humidity falls into the lower teens. Critical RH values will occur east of the Divide as well, however winds are not expected to gust as high until late this afternoon into the evening. The Cody Foothills and portions of the Wind River Basin will be borderline for critical fire weather conditions and will monitor later this morning whether to add to the Red Flag Warning or not. The Rangeland Fire Danger statement will cover where either winds or RH will be marginal for critical fire weather conditions. Models continue to trend PoPs downward over northwest portions along the front this evening. So, little to no showers or thunderstorms are expected. North-northwest winds with gusts up to 45 mph will occur across northern portions of the Bighorn Basin and Johnson County tonight, as the cold front moves through these areas. These winds will decrease to gusts up to 25 mph by sunrise Monday morning, as the cold front slowly continues southward. It will still be located across portions of Sweetwater and Lincoln counties Monday afternoon. As such, critical fire weather conditions (Wind gusts up to 35 mph and RH values in the lower teens) will continue across this area Monday afternoon. Temperatures will be cooler over northern and central portions, as a result of the frontal passage. .LONG TERM...Tuesday through Sunday Tuesday's forecast will continue with northwest flow as the ridge begins to rebuild across the region. The ridge does not fully set in until the later half of the week and by the weekend, southerly flow and some weak monsoonal moisture looks to once again set in over the region. Both the ECMWF and the GFS continue to be in pretty good agreement through next weekend. The ECMWF is by far the wetter model, but it tends to overdo convection extent, especially in the long term, so leaning more towards a middle ground between the two models for PoPs. This middle ground aligns pretty well with the NBM so little to no change to the PoPs in the grids. Best chances of convection and moisture will be next weekend, once the southerly flow is well established. In terms of temperatures, will continue with 90s east of the Divide and upper 80s to near 90 west of the Divide by the middle of the week and continuing into the weekend. Not looking at any triple digits at this time, as we are getting later in the summer and the ridge will not be as intense as we saw in July. Winds also will be fairly light under the ridge. Prior to the ridge building in, northwest flow through mid-week will be a bit breezier and with dry weather, could be looking at elevated, but not critical, fire weather through Wednesday. However, with the increasing moisture later in the week, fire weather concerns will be pretty well mitigated through most of the extended forecast period. && .AVIATION...For the 00Z TAFS through 00Z Tuesday Gusty winds will begin to diminish over the next few hours with a noticeable decrease by around sunset. Some isolated showers and thunderstorms are possible across the far north overnight with greatest chances at KCOD and KJAC. Otherwise, all terminals should remain dry with VFR conditions through the period. Wildfire smoke will continue to impact the region, but is not expected to impact terminal visibility. Mountain obscurations are expected through the period as a result of the smoke. && .FIRE WEATHER... Dry and not as smoky this morning. This will change however, as an additional round of smoke is expected to infiltrate back over the forecast area through the day today. Winds will also increase across western and southern portions this afternoon, in response to an approaching cold front. A Red Flag Warning remains in effect across southern zones, where critical fire weather conditions will occur. Wind gusts up to 35 mph will occur across the west, however RH values will only drop into the lower to middle 20s. Little to no precipitation is expected across the northwest along the front this evening. North-northwest wind with gusts up to 45 mph will occur behind the front tonight over portions of zones 275/276/281. Critical fire weather conditions will return across the southern zones Monday afternoon, as the cold front slowly progresses through the area. Temperatures will be cooler over northern and central portions Monday afternoon, in the wake of the cold front. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning from noon to 8 PM MDT Monday for WYZ288-414-416. Red Flag Warning until 8 PM MDT Monday for WYZ277>279-289. && SHORT TERM...LaVoie LONG TERM...Fisher AVIATION...Fisher FIRE WEATHER...LaVoie
Hazardous Weather Outlook National Weather Service Riverton WY 149 PM MDT Sun Aug 8 2021 WYZ001>020-022>030-092000- Yellowstone National Park-Absaroka Mountains-Cody Foothills- North Big Horn Basin-Southwest Big Horn Basin- Southeast Big Horn Basin-Owl Creek and Bridger Mountains- Bighorn Mountains West-Bighorn Mountains Southeast- Northeast Johnson County-Southeast Johnson County- Teton and Gros Ventre Mountains-Jackson Hole- Wind River Mountains West-Wind River Mountains East- Upper Wind River Basin-Wind River Basin-Lander Foothills- Green Mountains and Rattlesnake Range- Natrona County Lower Elevations-Casper Mountain-Star Valley- Salt River and Wyoming Ranges-Upper Green River Basin Foothills- Upper Green River Basin-South Lincoln County- Rock Springs and Green River-Flaming Gorge-East Sweetwater County- 149 PM MDT Sun Aug 8 2021 ...Red Flag Warning in effect across southern Wyoming Today and Monday Afternoon and Evening... This Hazardous Weather Outlook is for Western and Central Wyoming. .DAY ONE...This Afternoon and Tonight. Critical fire weather conditions will occur across southern Wyoming this afternoon and evening. Elevated fire weather danger is likely elsewhere. .DAYS TWO THROUGH SEVEN...Monday through Saturday. Monday...Critical fire weather conditions will return across southern portions of Wyoming. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures.
Special Weather Statement National Weather Service Riverton WY 647 PM MDT Sun Aug 8 2021 WYZ003>006-090500- Cody Foothills-North Big Horn Basin-Southwest Big Horn Basin- Southeast Big Horn Basin- Including the cities of Clark, Cody, Meeteetse, Basin, Greybull, Lovell, Powell, Shell, Thermopolis, Ten Sleep, and Worland 647 PM MDT Sun Aug 8 2021 ...Strong Cold Front to Reach Northern Wyoming Between 7 and 8 PM... This is a special weather statement from the National Weather Service Office in Riverton. * WHAT...Strong cold front moving south from Montana * WHERE...Northern Bighorn Basin * WHEN...The cold front will move into northern Park and Big Horn counties between 7 and 8 PM. The front will continue a steady march south and reach Thermopolis between 10 and 11 PM. * ADDITIONAL DETAILS...Temperatures will drop 15 to 20 degrees in about 30 minutes following frontal passage. A gusty north wind of 20 to 30 mph with gusts to around 45 mph can be expected for an hour or two after the cold front sweeps through.
The national radar mosaic for the moment the first event began.
2 high wind. Local standard time, as filed.
A maximum wind gust of 62 mph was recorded at Frannie. Winds were sustained at over 40 mph for an hour and a half. A wind gust of 59 mph was recorded at the South Big Horn County airport in Greybull.
There were numerous reports of high wind across northern Johnson County. A wind gust of 73 mph was recorded northeast of Buffalo. The ASOS at Johnson County Airport clocked a maximum wind gust of 69 mph.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2021Every state in 2021This day in weather historyWarnings in Wyoming, August 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 971532, 971533.