A squall line developed over northern Utah and produced widespread severe wind gusts and damage.
Every event with a place to put it; 4 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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 SLC wrote it up.
A squall line developed over northern Utah and produced widespread severe wind gusts and damage.
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 Salt Lake City, UT wrote its last area forecast discussion before the first event at Aug 21, 11:56 AM MST, 3 hours 44 minutes earlier.
Area Forecast Discussion National Weather Service Salt Lake City UT 1256 PM MDT Sat Aug 21 2021 .SYNOPSIS...A Pacific storm system will push a cold front through northern Utah and southwest Wyoming this afternoon and evening. A dry southwesterly flow will follow for early next week. && .SHORT TERM (Through 12Z Tuesday)... Forecast remains on track this morning with the main impacts across the region today being breezy pre-frontal southwesterly winds followed by showers and thunderstorms across northern Utah mid to late afternoon through this evening with a marginal threat of severe weather, primarily strong to damaging wind gusts. Satellite imagery shows a Pacific trough still digging southeastward settling into central Oregon, with a baroclinic leaf extending from northern Nevada across far northwest Utah into Idaho marking the baroclinic zone that will push eastward across northern Utah later today. Ahead of this, a sheared out wave ejected across Utah this morning has pushed weak showers through central as well as advected in deeper moisture into central Utah. Clearing skies behind this wave are allowing for efficient diurnal heating ahead of the upstream cold front. Meanwhile, 12Z SLC sounding showed steeping low level lapse rates already, but with an inversion around 500 mb. Aircraft soundings from SLC show this inversion layer decaying, and this trend is expected to continue as the upper-level trough continues to move closer to northern Utah this afternoon. This will allow for around 500-1000 J/kg of CAPE to develop across northern Utah this afternoon, with lesser amounts southward away from the upper-level cold pool. Unidirectional southwesterly flow will increase, along with speed shear as upper-level jet moves over northern Utah, which will also increase large scale synoptic ascent. Thus expect thunderstorms to develop by mid afternoon across northwest Utah, along and just ahead of the front and baroclinic zone. The mean trough will slide eastward through this evening, pushing the baroclinic zone across northern Utah. Thus thunderstorms should upscale into a line with shear supporting organized line segments which will be capable of strong to damaging wind gusts. The orientation of and track of the front will keep this threat confined to areas from Tooele and Salt Lake counties northward, as well as into southwest Wyoming. There is some potential for training storms and locally heavier rainfall where the flow better parallels the front north of Salt Lake County to the Idaho Border, which is also where overall precipitation totals should be highest. The front is expected to stall it southward progress around southern Tooele/ Northern Utah counties this evening, which will keep shower and thunderstorm chances much lower toward Provo and southward, with little precipitation expected. The HRRR model unfortunately brings a concentrated band of smoke into northern Utah once again tonight through Sunday, with some improving conditions forecast Monday. This improvement is owing to a dry southwesterly flow which will develop in the wake of the departing trough, which will also bring a slight warming trend heading into early next week. Sunday and Monday will feature temperatures returning closer to normal, but still just slightly below normal with dry conditions as high pressure builds back in across the region. .LONG TERM (After 12Z Tuesday)... The first half of the extended forecast period will be dominated by troughing to the northwest and an elongated ridge of high pressure to the east. The interplay between the two features will drive a southwest flow pattern with generally dry air being advected in from upstream. This rather benign setup will see temperatures running near average statewide with few to no impacts outside of isolated critical fire weather conditions over far southwestern Utah. By Thursday, the Pacific Northwest trough lifts out and shifts to the east, with a growing degree of uncertainty in ensemble solutions as to what may follow. The mean and most likely scenario suggests zonal flow will set up over the Great Basin to the Pacific Coast, continuing to bring dry and slightly warmer conditions to the region. This would also bring with it the potential to transport smoke from distant fires into the region once again. A few ensemble members diverge, and highlight a trough of low pressure moving into the Great Basin, with just enough of a southerly flow component to advect moisture into the far southeastern portion of the forecast area by the end of the period. && .AVIATION... KSLC...VFR conditions are expected to persist throughout the valid TAF period with a brief drop to MVFR with thunderstorms on site. Enhanced southerly winds will continue throughout the afternoon into the early evening. Potential for convective activity will increase after 23Z, with the primary threat occurring with the passage of an organized line of storms after 00Z. While flow is expected to shift out of the northwest behind this boundary, these thunderstorms will be capable of producing gusty and erratic winds from all directions as they move through the valley. REST OF UTAH AND SOUTHWEST WYOMING...Windy conditions will continue into and through this evening. Along and north of a KENV to KSLC line, numerous showers and thunderstorms are expected this afternoon and evening, with some potential in the KPVU and KHCR areas. Any storms that do develop will be capable of producing gusty and erratic winds. Dangerous microburst or downburst winds are possible in the vicinity of strong storms. Aside from any ceilings and reduced visibilities associated with convective activity, VFR conditions will prevail. && .FIRE WEATHER... A low pressure system over the Pacific Northwest will push a cold front through northern Utah this afternoon and evening. Ahead of this system gusty southwest winds will develop across the region, however with cooler temperatures remaining in place daytime minimum humidity values will remain in the 20 percent range across central and southern Utah, and in the 30 percent range across the north. Thunderstorms will develop along and ahead of this cold front across northwest Utah this afternoon and move eastward across the Wasatch Front and into the northern mountains by evening. These storms will bring strong gusty winds along with a wind shift to the northwest behind the frontal passage. Again this could warrant critical fire weather conditions due to lightning and gusty winds, however the last storm system brought appreciable precipitation across northern Utah and there has been not been much time for drying. Otherwise, additional wetting rains are expected across northern Utah late Saturday and Saturday night. As this system moves east of the area, a dry southwesterly flow will develop beginning Sunday, and continuing through the first half of next week. This will bring a warming trend with dry conditions across the area. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && SHORT TERM...Church LONG TERM...Wessler AVIATION...Wessler FIRE WEATHER...Church For more information from NOAA's National Weather Service visit... http://weather.gov/saltlakecity For frequently asked questions about the Area Forecast Discussion visit... http://weather.gov/saltlakecity/general/afd_faqs.php
Special Weather Statement
National Weather Service Salt Lake City UT
125 PM MDT Sat Aug 21 2021
UTZ109-110-212015-
Bear Lake and Bear River Valley UT-Wasatch Mountains I-80 North UT-
125 PM MDT Sat Aug 21 2021
...A strong thunderstorm will impact portions of northeastern Cache
and northwestern Rich Counties through 215 PM MDT...
At 125 PM MDT, Doppler radar was tracking a strong thunderstorm near
Garden, or near Laketown, moving northeast at 35 mph.
HAZARD...Wind gusts up to 50 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Laketown, Bear Lake Idaho Portion, Garden City, Garden, Bear Lake,
Meadowville, Pickelville and Lakota.
This storm will be capable of producing strong gusty winds on Bear
Lake. This will lead to a sudden increase in waves and very choppy
waters which will result in hazardous boating conditions. Boaters are
urged to seek safe harbor if possible.
This includes the following highways...
US Route 89 between mile markers 489 and 502.
Utah Route 30 between mile markers 110 and 123.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 4170 11135 4178 11157 4200 11150 4201 11127
4200 11111
TIME...MOT...LOC 1925Z 204DEG 32KT 4182 11141
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH
WebberSpecial Weather Statement
National Weather Service Salt Lake City UT
155 PM MDT Sat Aug 21 2021
UTZ103-110-212045-
Eastern Box Elder County UT-Wasatch Mountains I-80 North UT-
155 PM MDT Sat Aug 21 2021
...A strong thunderstorm will impact portions of northwestern Cache
and northeastern Box Elder Counties through 245 PM MDT...
At 155 PM MDT, Doppler radar was tracking a strong thunderstorm 10
miles west of Plymouth, or 18 miles south of Malad, moving northeast
at 25 mph.
HAZARD...Wind gusts up to 50 mph and pea size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible.
Locations impacted include...
Portage and Washakie.
This includes Interstate 15 between mile markers 395 and 400.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 4181 11226 4189 11247 4200 11242 4200 11211
TIME...MOT...LOC 1955Z 205DEG 22KT 4192 11232
MAX HAIL SIZE...0.25 IN
MAX WIND GUST...50 MPH
WebberSpecial Weather Statement
National Weather Service Salt Lake City UT
314 PM MDT Sat Aug 21 2021
UTZ101-103-212215-
Eastern Box Elder County UT-Great Salt Lake Desert and Mountains UT-
314 PM MDT Sat Aug 21 2021
...Strong thunderstorms will impact portions of Box Elder and
northwestern Tooele Counties through 415 PM MDT...
At 313 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Snowville to 15 miles north of West
Wendover. Movement was northeast at 45 mph.
HAZARD...Wind gusts up to 50 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Snowville, Howell, Park Valley, Utah Test and Training Range North,
Great Salt Lake North of the Causeway, Portage, Washakie, Promontory,
Gunnison Island, Locomotive Springs, Lakeside, Curlew Junction,
Lucin, Rosette, Golden Spike Historic Site and Bonneville Salt Flats.
This includes the following highways...
Interstate 15 between mile markers 398 and 400.
Interstate 84 between mile markers 0 and 32.
Utah Route 30 between mile markers 1 and 90.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 4198 11217 4085 11297 4084 11404 4143 11404
4200 11315 4200 11219
TIME...MOT...LOC 2113Z 235DEG 41KT 4196 11279 4099 11409
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH
WebberSpecial Weather Statement
National Weather Service Salt Lake City UT
431 PM MDT Sat Aug 21 2021
UTZ101-212330-
Great Salt Lake Desert and Mountains UT-
431 PM MDT Sat Aug 21 2021
...Strong thunderstorms will impact portions of south central Box
Elder and northwestern Tooele Counties through 530 PM MDT...
At 431 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 18 miles northwest of Knolls to 19 miles
southeast of Wendover. Movement was northeast at 50 mph.
HAZARD...Wind gusts up to 50 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Utah Test and Training Range South, Knolls, Utah Test and Training
Range North and Clive.
This includes Interstate 80 in Utah between mile markers 18 and 65.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 4115 11271 4048 11295 4034 11396 4104 11354
TIME...MOT...LOC 2231Z 240DEG 42KT 4090 11354 4048 11385
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH
WebberSpecial Weather Statement
National Weather Service Salt Lake City UT
434 PM MDT Sat Aug 21 2021
UTZ101-103-107-110-212330-
Eastern Box Elder County UT-Wasatch Mountains I-80 North UT-
Cache Valley/Utah Portion UT-Great Salt Lake Desert and Mountains UT-
434 PM MDT Sat Aug 21 2021
...Strong thunderstorms will impact portions of northwestern Cache
and northeastern Box Elder Counties through 530 PM MDT...
At 433 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 9 miles southwest of Cherry Creek Rest Area to
9 miles northeast of Great Salt Lake North of the Causeway. Movement
was northeast at 50 mph.
HAZARD...Wind gusts up to 50 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Logan, Brigham City, Tremonton, Cache, Smithfield, Hyrum, Wellsville,
Lewiston, Bear River City, Corinne, Clarkston, Trenton, Plymouth,
Howell, Utah State University, Benson, Peter, Riverside, Great Salt
Lake North of the Causeway and North Logan.
This includes the following highways...
Interstate 15 between mile markers 365 and 400.
Interstate 84 between mile markers 24 and 42.
US Route 89 between mile markers 459 and 466.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 4155 11180 4142 11275 4200 11235 4200 11158
TIME...MOT...LOC 2233Z 235DEG 43KT 4198 11233 4153 11270
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH
WebberThe Salt Lake City radar (KMTX), 144 km away, was scanning. The volume nearest the first event began at 22:42 UTC.
40 thunderstorm wind, 4 high wind, 1 heavy rain. Local standard time, as filed.
The Interstate 80 at Milepost 1 automated weather station reported a gust of 59 mph.
The Wendover Airport automated weather station recorded a peak wind gust of 61 mph.
The Interstate 80 at Milepost 71 automated weather station recorded a peak wind gust of 61 mph.
The Interstate 80 at Milepost 68 automated weather station recorded a peak wind gust of 60 mph.
The Promontory Point automated weather station recorded a peak wind gust of 60 mph.
The Lakeside Mountain automated weather station recorded a peak wind gust of 63 mph.
The Promontory Point automated weather station recorded a peak wind gust of 64 mph.
The Solar Union Pacific Railroad automated weather station recorded a peak wind gust of 58 mph.
The Lower Cedar Mountain automated weather station recorded a peak wind gust of 59 mph.
A tree fell on a fence near Fruit Heights.
The Promontory Point automated weather station recorded a peak wind gust of 61 mph.
The Lake Point Interstate 80 automated weather station recorded a peak wind gust of 73 mph.
A tree fell into a house near Hill Air Force Base.
The Promontory Point automated weather station recorded a peak wind gust of 62 mph.
The Snowbasin Resort Ogden Peak automated weather station recorded a peak wind gust of 67 mph.
A National Weather Service employee measured a 65 mph wind gust, and reported downed tree branches.
The Center Tailings automated weather station recorded a peak wind gust of 59 mph.
The U.S. Highway 89 at Park Lane automated weather station recorded a peak wind gust of 66 mph.
A personal automated weather station in Farmington measured a wind gust of 63 mph.
The CENEWS Union Pacific Railroad automated weather station in Farmington recorded a peak wind gust of 59 mph.
A power pole snapped and fell across the road at 2400 South and 500 West in Bountiful.
The Centerville automated weather station recorded a peak wind gust of 63 mph.
The Legacy Parkway automated weather station recorded a peak wind gust of 59 mph.
Tree branches were downed at Lagoon Amusement Park.
The Promontory Point automated weather station recorded a peak wind gust of 58 mph.
Two trees were blown down in Ogden Canyon, with limbs landing on two vehicles.
The Trappers Loop Road automated weather station recorded a peak wind gust of 63 mph.
The Great Salt Lake Minerals automated weather station recorded a peak wind gust of 58 mph.
The Midfield Federal Aviation Administration automated weather station at Salt Lake City International Airport recorded a peak wind gust of 63 mph.
A tree was downed in Rose Park.
Multiple trees were blown over in Clinton.
A tree fell onto a road in the Avenues neighborhood.
The University of Utah William Browning Building automated weather station recorded a peak wind gust of 62 mph.
The Parley's Canyon at Quarry automated weather station recorded a peak wind gust of 58 mph.
A tree was blown down in Taylorsville.
The Otter Creek automated weather station recorded a peak wind gust of 59 mph.
In the wake of a thunderstorms complex, winds increased across the Great Salt Lake Desert and Mountains. Automated weather station recorded peak wind gusts included 68 mph at Interstate 80 at Knolls, 63 mph at Callao, and 62 mph at Wildcat Mountain.
The Flight Park South automated weather station recorded a peak wind gust of 67 mph.
A 60-foot-tall pine tree fell on 2 people, injuring 1.
The Point of the Mountain automated weather station recorded a peak wind gust of 65 mph.
The Pioneer Crossing automated weather station recorded a peak wind gust of 58 mph.
A video indicated street flooding in North Salt Lake.
A cold pool in the wake of a thunderstorm generated a localized downslope wind event in northern Utah County, with wind gusts up to 70 mph measured.
In the wake of a thunderstorm complex, winds increased across the Tooele Valley. Automated weather station recorded peak wind gusts included 60 mph at Interstate 80 at Timpie and 58 mph at State Route 201 at Interstate 80.
In the wake of a thunderstorm complex, winds increased across the Salt Lake Valley. Automated weather station recorded peak wind gusts included 62 mph at Beach and 58 mph at Trans-Jordan Landfill.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Utah in 2021Every state in 2021This day in weather historyWarnings in Utah, 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: 982962, 983101, 982970, 982973, 982974, 982981, 982983, 982979, 982987, 982992, 982994, 983006, 982996, 982999, 983032, 983004, 983009, 983110, 983012, 983113, 983015, 983020, 983025, 983029, 983030, 983034, 983054, 983121, 983038, 983039, 983041, 983045, 983050, 983126, 983056, 983059, 983159, 983063, 983065, 983131, and more.