An intense supercell thunderstorm originated near Chugwater, Wyoming, during the early to mid afternoon hours on 6/20, tracking across southern Platte and Goshen counties through approximately 3:00 PM MDT before moving into the western Nebraska Panhandle. 5 inches in diameter along with wind gusts in excess of 70 MPH, noting that they had never seen that large of hail coinciding with such…
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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 CYS wrote it up.
An intense supercell thunderstorm originated near Chugwater, Wyoming, during the early to mid afternoon hours on 6/20, tracking across southern Platte and Goshen counties through approximately 3:00 PM MDT before moving into the western Nebraska Panhandle. Storm chasers reported extremely large and destructive hail up to 4.5 inches in diameter along with wind gusts in excess of 70 MPH, noting that they had never seen that large of hail coinciding with such intense winds.
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 Jun 20, 11:15 AM MST, 1 hour 51 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Cheyenne WY 1215 PM MDT Thu Jun 20 2024 .KEY MESSAGES... - Severe thunderstorms possible this afternoon with hail, strong winds, and heavy rainfall. Cannot rule out a tornado with any longer track supercells that develop. Severe thunderstorm potential continues Friday. - Hot temperatures are expected for Sunday through the middle of next week. Highs exceeding 100F will be possible (40-60% chance) particularly on Monday. && .MESOSCALE... Issued at 1153 AM MDT Thu Jun 20 2024 Mesoscale trends continue to be monitored ahead of today's severe weather event in southeast Wyoming and western Nebraska. As of 18z/noon, high-based convective towers were noted along and just west of the Laramie Range in southeast Wyoming where dewpoints are generally in the upper-30s and low-40s with southwesterly surface winds. A dryline boundary was noted on KCYS radar imagery over the south Laramie range, which per surface observations likely extends northward along the western fringes of the Laramie Range and into the Shirley Basin. East of this boundary and into the high plains, easterly surface winds are transporting rich surface moisture toward the dryline boundary in general east-southeasterly flow. With 30-40 knots of southwesterly flow aloft, bulk shear values AoA 45 knots are in place over the high plains. Several important nuances in satellite and surface observations are evident that may ultimately assist with zeroing in on the greatest threat zone today. The character of surface cloud cover in the eastern Wyoming high plains depicts a gradient of stabilization, also evident in wind/Td fields. In far southeast Wyoming over CYS, low- level cloud cover has generally mixed out late in the morning giving way to clear skies and lower dewpoint values as a relatively shallow moist layer mixes away. Farther north in central Platte and Goshen counties, surface cumulus clouds over the North Platte River valley from BFF through TOR and GUR have remained in place despite surface mixing and heating. With surface dewpoints remaining in the low 60s and more backed winds to the east compared with locations farther south, a favorable combination of deeper surface moisture and better low-level hodograph shape exists here. Even farther north along the US-20 corridor from Douglas through Lusk/Chadron, morning convection has draped an outflow boundary along this corridor with backed northeasterly flow north of this feature. It is likely that conditions will remain capped to the north of this boundary today given plentiful lingering mid- level cloud cover. With all this being said, the most favorable overlap of surface moisture, better directional wind shear, and upper-level support appears to be throughout Platte and Goshen County Wyoming as well as points farther east through Scottsbluff and Alliance. Mid-morning CAM guidance has continuously depicted initially discrete supercell activity here, eventually merging into a linear storm mode as outflows pool. Hail early in storm mode, then high winds later in the day appear to be the most likely threats. The tornado threat will likely be dependent on if any initial discrete cells can tap into enhanced low-level shear near/along the lingering outflow boundary in far northern Platte, Goshen, Sioux and Dawes counties. These features will continue to be monitored throughout the early afternoon. && .SHORT TERM /THROUGH FRIDAY/... Issued at 403 AM MDT Thu Jun 20 2024 Latest GOES imagery shows a weak shortwave passing over the central Rockies with showers and thunderstorms from central CO extending northeast towards Cheyenne Co, NE where latest GLM picked up a couple flashes. Strong southeasterly moisture advection has brought near 60F degree dew points to the NE panhandle along with low clouds and patchy fog. A Dense Fog Advisory remains in effect this morning for the South Laramie Range including I-80 between Cheyenne and Laramie where reported visibilities have been under one-quarter mile all night. This afternoon is shaping up to be an active severe weather day across southeast WY and western NE. With the aforementioned southeasterly moisture advection into the area along with WAA, a notable capping inversion will need to be broken for CI across the NE panhandle today. However, CI over the higher terrain further west with a passing leading shortwave looks to kick things off today with storms developing as early as late this morning across the Laramie Range. MLCAPE values exceeding 1500 J/kg appear likely with the capping inversion breaking in areas of clouds clearing later this morning through the early afternoon. With southerly flow across the Cheyenne Ridge, enhanced convergence will be present across southern Platte/Goshen Co with a Chugwater cyclone setup reminiscent of the setup late last June. Hail, strong winds, and heavy rainfall are likely today with the stronger cells, and cannot rule out a tornado with any longer track supercells that develop. Vertical profiles lack any significant dry layers limiting hail potential, but overall moist soundings with 1-1.25" PW values would be supportive of efficient rain producers and localized flooding with any training storms. Southeasterly surface winds veering aloft will support modest curvature of the low- level hodograph, through SRH values are slightly limited by a shallow southerly flow layer before quickly transitioning to southwesterly aloft. While initially discrete, hi-res guidance grows storms upscale across the NE panhandle late in the afternoon with storms pushing east into central NE early this evening. HREF 40 dBZ paintballs show a notable difference in timing with a member (NAMNest) being slightly delayed with CI and eastward propagation. It appears overnight convection from the model in eastern CO may try to enhance the capping inversion in our area and therefore delaying CI. However, model depiction compared to latest radar imagery would suggest overdone coverage of storms, but will need to continue to monitor through the morning. Friday will bring another chance for showers and thunderstorms across the CWA with more widespread coverage as the trough axis passes through. A stationary boundary positioned along the inverted trough extending out of northeast CO through central WY will enhance moisture convergence with upper 50F degree dew points off to the northeast. Storm coverage will increase by late morning with favorable lift associated with 100 kt 250mb jet extending into the north-central CONUS. Storms will likely increase in intensity but remain elevated upon crossing the moisture boundary by mid-afternoon where the latest RAP forecasts 1500+ J/kg of MLCAPE and 40 kt of effective shear. Storms will likely grow upscale quickly with larger scale lift present, but could see a brief window for large hail production before shifting the focus to a wind and heavy rainfall threat. SPC has highlighted portions of the CWA with a Day 2 Slight Risk for Severe Thunderstorms. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Issued at 403 AM MDT Thu Jun 20 2024 A hot and largely dry weather pattern will dominate much of the week ahead. Friday's shortwave trough will be off to our east by early Saturday morning, leaving dry air advection over much of our area in its wake. The shortwave moving east will break down the potent ridge that has been dominant over the central and eastern US this week. However, the ridge will then retrograde westward and expand over the Four Corners states through the weekend. Models are in good agreement showing the ridge remaining fairly stationary but amplifying through the middle of next week. Ensemble mean 500-mb heights over KCYS climb from around 587-dm at 12z Saturday to a maximum of 592-dm by Tuesday evening. Temperatures should return above normal on Saturday as 700-mb temps climb to around +15C over the Wyoming portion of the forecast area. Widespread 80s to lower 90s will still probably be the coolest day of the long term forecast period. By Sunday, 700-mb temperatures edge up to +16 to +18C and remain there or higher through at least Tuesday, and possibly beyond. Look for widespread 90s on Sunday, and possibly a few degrees higher on Monday. Some areas will have a good chance at surpassing 100F. Current probabilities of 100+F temperatures on Monday are sitting around 40% for Chadron, Torrington, and Bridgeport, but over 60% for Scottsbluff. Forecast confidence decreases somewhat beyond Monday, as the amplifying ridge may open the door to a few weak shortwaves sliding over the top. Some of these could have the potential to bring surface cold fronts through the area. While there is nearly every ensemble member has extremely hot temperatures on Sunday and Monday, about 20% of members bring a front through our northern counties by Tuesday, and this proportion rises for Wednesday and Thursday. Overall, the forecast still leans quite hot, but by mid-week there is a little bit more uncertainty. Other than the heat, the week ahead looks fairly dry too. Precipitable water values don't look too bad, hovering around average for Saturday into early next week. However, the combination of dry low-levels (due to the dry-line getting pulled eastward) and warm air aloft will reduce precipitation chances. We should still see some activity each day, but it will be much less widespread than Thursday and Friday. With inverted-v soundings showing up in the forecast in place of decent mid to upper level moisture lingering, expect each day to put up some scattered radar echos, but the chance for measurable precipitation on the ground looks fairly low. Showers may lead to dry microbursts through this hot period. The majority of ensemble members allow the dryline to pull back to the west by Tuesday or Wednesday, increasing low level moisture and thus the chance for more noteworthy precipitation and thunderstorm activity for the middle of the week. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1131 AM MDT Thu Jun 20 2024 Thunderstorms are the main issue this afternoon across southeast Wyoming and Nebraska Panhandle. Using HRRR and RAP simulated radar for timing and locations of storms. Lower flight conditions tonight across the northern Nebraska Panhandle with easterly winds continuing overnight. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && MESOSCALE...MAC SHORT TERM...MB LONG TERM...MN AVIATION...GCC
Hazardous Weather Outlook National Weather Service Cheyenne WY 413 AM MDT Thu Jun 20 2024 NEZ002-003-019>021-054-055-095-096-WYZ101>119-211015- Dawes County-Box Butte County-Scotts Bluff County-Banner County- Morrill County-Kimball County-Cheyenne 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-Snowy Range- Laramie Valley-South Laramie Range-South Laramie Range Foothills- Central Laramie County-East Laramie County- 413 AM MDT Thu Jun 20 2024 This hazardous weather outlook is for portions of panhandle Nebraska...east central Wyoming...south central Wyoming and southeast Wyoming. .DAY ONE...TODAY AND TONIGHT Severe thunderstorms possible this afternoon with hail, strong winds, and heavy rainfall. Cannot rule out a tornado with any longer track supercells that develop. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY Severe thunderstorm potential continues Friday. Hot temperatures are expected for Sunday through the middle of next week. Highs exceeding 100F will be possible (40-60% chance) particularly on Monday. .Spotter information statement... Please report any severe weather later today to the NWS Cheyenne office.
Special Weather Statement
National Weather Service Cheyenne WY
123 PM MDT Thu Jun 20 2024
WYZ106-107-117-202000-
East Platte County WY-
Central Laramie Range and Southwest Platte County WY-
South Laramie Range Foothills WY-
123 PM MDT Thu Jun 20 2024
...A STRONG THUNDERSTORM WILL IMPACT NORTHWESTERN LARAMIE AND
SOUTHWESTERN PLATTE COUNTIES THROUGH 200 PM MDT...
At 123 PM MDT, Doppler radar was tracking a strong thunderstorm 9
miles southeast of Sybille Canyon, or 30 miles southwest of
Wheatland, moving northeast at 30 mph.
HAZARD...Wind gusts up to 50 mph and nickel size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor hail damage to vegetation is
possible.
This storm will remain over mainly rural areas of northwestern
Laramie and southwestern Platte Counties.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Cheyenne.
A Severe Thunderstorm Watch remains in effect until 700 PM MDT for
southeastern Wyoming.
&&
LAT...LON 4162 10527 4172 10527 4185 10511 4177 10498
4166 10498
TIME...MOT...LOC 1923Z 238DEG 27KT 4167 10524
MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH
HammerSpecial Weather Statement
National Weather Service Cheyenne WY
136 PM MDT Thu Jun 20 2024
WYZ106-107-202000-
East Platte County WY-
Central Laramie Range and Southwest Platte County WY-
136 PM MDT Thu Jun 20 2024
...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN PLATTE COUNTY
THROUGH 200 PM MDT...
At 135 PM MDT, Doppler radar was tracking a strong thunderstorm 7
miles northwest of Chugwater, or 16 miles south of Wheatland, moving
northeast at 25 mph.
HAZARD...Wind gusts up to 50 mph and nickel size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor hail damage to vegetation is
possible.
Locations impacted include...
Chugwater, Slater, and Antelope Gap.
This includes Interstate 25 in Wyoming between mile markers 49 and
71.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Cheyenne.
A Severe Thunderstorm Watch remains in effect until 700 PM MDT for
southeastern Wyoming.
&&
LAT...LON 4170 10509 4181 10515 4205 10479 4193 10466
4166 10466
TIME...MOT...LOC 1935Z 236DEG 20KT 4181 10494
MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH
HammerPreliminary Local Storm Report
National Weather Service Cheyenne WY
206 PM MDT Thu Jun 20 2024
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0204 PM Hail 12 SSE Horse Creek 41.25N 105.09W
06/20/2024 E0.50 inch Laramie WY Trained Spotter
&&
Event Number CYS2400014
kmdThe Cheyenne radar (KCYS), 87 km away, was scanning. The volume nearest the first event began at 20:04 UTC.
9 hail, 3 thunderstorm wind, 1 tornado, 1 flash flood. Local standard time, as filed.
A wind gust to 58 MPH was recorded at the Bordeaux WYDOT sensor.
The public reported hail up to the size of golf balls with hail accumulating in fields in the Slater area.
A wind gust to 63 MPH was recorded at the Bordeaux WYDOT sensor.
A trained weather spotter reported half dollar sized hail 15 miles SE of Wheatland.
The public reported quarter to golf ball sized hail 3 miles S of Slater.
A trained weather spotter reported ping pong ball sized hail 8 miles WSW of Yoder.
A brief tornado was observed in rural Goshen County by numerous storm spotters|and emergency management personnel. Due to the rural nature of this tornado, only|limited damage to fencing was found, as well as scattered plant debris. Review of|video and photo sequences along with radar time-matching indicate that this tornado|likely began as a landspout, but quickly gained mesocyclonic characteristics as it|interacted with the updraft base, condensed a funnel, and slowed/occluded into the|storm. Regardless, without any damage of note this tornado will be recorded as EF-U.
A trained weather spotter reported tennis ball sized hail 9 miles NW of Hawk Springs.
Hail up to 4.5 inches in diameter was reported 6 miles NW of Hawk Springs.
A wind gust to 59 MPH was measured by a car roof anemometer in Hawk Springs.
A storm chaser reported 4+ inch diameter hail with wind gusts 60-70 MPH 4 miles SSW of Yoder.
A trained weather spotter reported 4.5 inch diameter hail 1 mile S of Yoder.
The public reported 4.5 inch diameter hail in the town of Yoder.
A trained spotter reported County Road 205 underwater due to heavy rainfall.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2024Every state in 2024This day in weather historyThe tornado archive for Wyoming, 2024Warnings in Wyoming, June 2024
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: 1182114, 1182115, 1182117, 1182118, 1182120, 1182123, 1182130, 1182124, 1182125, 1182126, 1182127, 1182128, 1182129, 1192092.