Reverse gradient flow across the wind prone region of the North Snowy Range Foothills produced high winds in the afternoon and evening hours of the 22nd. Highest wind gust was 76 mph at Halleck Ridge along Interstate 80 located about seven miles northwest of Elk Mountain.
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The episode as NWS CYS wrote it up.
Reverse gradient flow across the wind prone region of the North Snowy Range Foothills produced high winds in the afternoon and evening hours of the 22nd. Highest wind gust was 76 mph at Halleck Ridge along Interstate 80 located about seven miles northwest of Elk Mountain.
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 Cheyenne, WY wrote its last area forecast discussion before the first event at May 22, 1:52 PM MST, 14 minutes earlier.
Area Forecast Discussion National Weather Service Cheyenne WY 252 PM MDT Sat May 22 2021 .SHORT TERM...(This evening through Monday night) Issued at 250 PM MDT Sat May 22 2021 This active pattern of afternoon showers and thunderstorms continues this afternoon and into the nighttime hours. A tight frontal boundary is keeping the cold air and low cloud ceilings in far southeast Wyoming and the Nebraska panhandle. Temperatures on the south side are in the 60s and 70s with dewpoints in the 60s, whereas temperatures on the north side are in the 40s to 50s with dewpoints in the 40s. The big question will be what the convection does as it crosses the frontal boundary into the colder temperatures and if it is able to sustain itself. Key Messages: 1) There is a Marginal (level 1 of 5) to Slight (level 2 of 5) Risk of severe weather for southeast Wyoming and western Nebraska Saturday and Sunday. The greatest confidence for isolated strong to briefly severe thunderstorms containing large hail (up to golf ball sized), gusty winds (greater than 60 MPH), and heavy rainfall, is in Cheyenne and Morrill Counties. A brief landspout can also not be ruled out for these areas. 2) The thunderstorms will form down in Colorado, then move northward. As they cross into the cold temperatures, they will likely weaken and move off northeastward. 3) There is a chance for flash flooding in the Mullen burn scar this afternoon and evening if showers and thunderstorms continuously move over the region. Weather details: Northerly winds have kept low clouds and fog in southeast Wyoming and western Nebraska, limiting the severe potential for much of the area. But, as the storms move up from Colorado and this stratiform precipitation that is currently falling continues to fall, it will erode the steep caps in place right now. If the caps do erode, Laramie, Platte, Goshen, Kimball, and Banner counties may also experience strong to briefly severe thunderstorms this evening. As of right now though, there is too much CIN compared to the very little CAPE to expect much of anything except stratiform precipitation for Laramie, Platte, Goshen, Kimball, and Banner counties. Sunday, current HiRes guidance shows a strong line of storms developing along the I-25 corridor around 1-2 PM MDT, pushing all the way through the Nebraska panhandle by 8 PM MDT. The main hazards in the strongest storms will strong, gusty winds above 60 MPH, hail up to golf ball sized, and brief heavy rainfall. CAPE values 1,000-1,500 J/kg combined with strong shear values oriented parallel to the boundary will contribute to strong thunderstorm formation. The greatest risk will be in the Nebraska panhandle. Monday, conditions dry out and some strong winds as a ridge moves into the region. Strongest winds are expected to be up to 50 MPH in northern Carbon County. Dewpoints drop to the 20s and 30s across southeast Wyoming and western Nebraska. .LONG TERM...(Tuesday through Saturday) Issued at 250 PM MDT Sat May 22 2021 Models still on track for the later part of next week with some embedded shortwaves pulsing through the region. This pattern should remain fairly consistent through late Tuesday as the upper level low is absorbed into the main flow. Some minor ridging is expected ahead of the shortwave feature. As we head towards the middle of the week, there is a chance for some afternoon rain and thunderstorms on Wednesday evening, with minor moisture advected into the region ahead of a minor trough digging east/southeast. Otherwise, drier air and much more pleasant conditions are expected with a ridging pattern into the region through Memorial Day Weekend. Afternoon high temperatures will trend above normal ranging from the the mid 70s to low 80s across southeastern Wyoming and the Nebraska Panhandle. Unfortunately, with these warmer and drier pattern, fire weather concerns begin to creep up with this weekend showing RH values in the low teens and some wind gusts upwards in the 25 mph range towards the western region of the CWA. && .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) Issued at 1145 AM MDT Sat May 22 2021 The main concern with this forecast is when the lower ceilings are expected to move out of the area. Latest surface observations and webcams in the Nebraska panhandle were showing areas of dense fog in the higher elevations mainly above 4000ft while on the Wyoming side, the cloud deck is a little higher due this cloud deck being thinner which is allowing for more solar radiation to penetrate the surface. These ceilings should begin to climb slowly towards the MVFR category in some locals during the remainder of the afternoon in response to better pressure falls. If these IFR ceilings persist longer into the afternoon, our convection chances will most likely be delayed until the late in the day or evening. For now, the best chances of convection will be in the Nebraska Panhandle this evening in response to the convection developing over northeast Colorado. However, we are not anticipating much more than a couple of storms that may produce some hail up to quarter size. Confidence is fairly low that we will see anything larger than dime size. Meanwhile, the fog and low IFR ceilings will move back into the picture tonight. && .FIRE WEATHER... Issued at 250 PM MDT Sat May 22 2021 Chances of showers and thunderstorms through Saturday and Sunday afternoon and evening for southeast Wyoming and western Nebraska. As the storms move through there is a chance of a wetting rain across Carbon County, WY, and Cheyenne and Morrill Counties, NE. Starting Monday we go into a pattern of very dry and windy elevated to critical fire weather conditions in southeast Wyoming and western Nebraska. Fuels are still in green-up and are not likely to burn, so Red Flag Warnings will not be issued, unless the fuel status changes. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && SHORT TERM...LK LONG TERM...MD AVIATION...REC FIRE WEATHER...LK
Hazardous Weather Outlook National Weather Service Cheyenne WY 520 AM MDT Sat May 22 2021 NEZ019>021-054-055-WYZ117>119-231130- Scotts Bluff County-Banner County-Morrill County-Kimball County- Cheyenne County-South Laramie Range Foothills- Central Laramie County-East Laramie County- 520 AM MDT Sat May 22 2021 This hazardous weather outlook is for portions of panhandle Nebraska and southeast Wyoming. .DAY ONE...TODAY AND TONIGHT Isolated strong to briefly severe storms will be possible this afternoon after 2 to 3pm through 9 to 10pm across Cheyenne County west to Kimball, Laramie and perhaps into Banner and Morrill Counties. Main hazards will be quarter to ping-pong size hail, localized 40-60 mph winds, and a brief landspout tornado can't be ruled out. Storms will decrease in coverage through the evening hours. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY Another round of strong to severe storms is expected to occur as a squall line develops in far east Wyoming early Sunday afternoon and sweeps across much of the Nebraska Panhandle through the afternoon hours. Main hazards will be straight-line winds of 60 to 70 mph, quarter to ping-pong hail and a brief tornado can't be ruled out as well. Storms will end and push east into central Nebraska by 6 to 7pm. Gradient winds will increase Sunday afternoon through Monday and reach upwards 30 to 40 mph as a strong weather system moves through behind the squall line. .Spotter information statement... Spotter activation will be needed today and again Sunday. NEZ002-003-095-096-WYZ101>113-115-116-231130- Dawes County-Box Butte County-Northern Sioux County- Southern Sioux County-Converse County Lower Elevations- Niobrara County-North Laramie Range- Ferris/Seminoe/Shirley Mountains-Shirley Basin- Central Laramie Range and Southwest Platte County- East Platte County-Goshen County-Central Carbon County- North Snowy Range Foothills-Southwest Carbon County- Sierra Madre Range-Upper North Platte River Basin-Laramie Valley- South Laramie Range- 520 AM MDT Sat May 22 2021 This hazardous weather outlook is for portions of panhandle Nebraska...east central Wyoming...south central Wyoming and southeast Wyoming. .DAY ONE...TODAY AND TONIGHT Scattered showers an a few thunderstorms will occur this afternoon. Occasional lighting and brief moderate rain could occur. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY Another round of strong to severe storms is expected to occur as a squall line develops in far east Wyoming early Sunday afternoon and sweeps across much of the Nebraska Panhandle through the afternoon hours. Main hazards will be straight-line winds of 60 to 70 mph, quarter to ping-pong hail and a brief tornado can't be ruled out as well. Storms will end and push east into central Nebraska by 6 to 7pm. Gradient winds will increase Sunday afternoon through Monday and reach upwards 30 to 40 mph as a strong weather system moves through behind the squall line. .Spotter information statement... Spotter activation will be needed Sunday. WYZ114-231130- Snowy Range- 520 AM MDT Sat May 22 2021 This hazardous weather outlook is for portions of south central Wyoming. .DAY ONE...TODAY AND TONIGHT Scattered rain showers and a few weak to at times, moderate thunderstorms could occur across the Snowys and near the Mullen Burn Scar this afternoon from 1pm to 8pm. Overall flash flooding risk is low but could become moderate if storms move over the same area this afternoon. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY The flash flooding risk on the Mullen Burn Scar will be none to limited Sunday and through early next week with a drier pattern in place. .Spotter information statement... Spotter activation may be needed today.
Special Weather Statement National Weather Service Cheyenne WY 909 AM MDT Sat May 22 2021 WYZ117-221800- South Laramie Range Foothills- Including the cities of Whitaker, Federal, and Horse Creek 909 AM MDT Sat May 22 2021 Patchy dense fog has formed along Interstate 25 from Cheyenne up to Wheatland. Patches of visibilities less than a quarter mile are likely until around noon. Maintain caution if traveling by keeping distance between vehicles and turning your headlights on. LK
Special Weather Statement National Weather Service Cheyenne WY 1203 PM MDT Sat May 22 2021 NEZ002-003-019>021-054-055-095-096-222000- Dawes County-Box Butte County-Scotts Bluff County-Banner County- Morrill County-Kimball County-Cheyenne County- Northern Sioux County-Southern Sioux County- Including the cities of Chadron, Chadron St Park, Alliance, Scottsbluff, Gering, Harrisburg, Angora, Bridgeport, Bayard, Redington, Kimball, Sidney, Brownson, Harrison, and Agate 1203 PM MDT Sat May 22 2021 Patchy dense fog has formed throughout the Nebraska panhandle. Patches of visibilities less than a quarter mile are likely until 2 PM MDT. Maintain caution if traveling by keeping distance between vehicles and turning your headlights on. LK
The national radar mosaic for the moment the first event began.
1 high wind. Local standard time, as filed.
Wyoming Department of Transportation sensor along Interstate 80 at Halleck Ridge or seven miles northwest of Elk Mountain measured the reported wind gust.
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, May 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: 950986.