Isolated summer thunderstorms produced localized flash flooding and hail in southern Utah.
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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 SLC wrote it up.
Isolated summer thunderstorms produced localized flash flooding and hail in southern Utah.
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 12, 3:07 PM MST, 1 hour 8 minutes earlier.
Area Forecast Discussion National Weather Service Salt Lake City UT 407 PM MDT Thu Aug 12 2021 .SYNOPSIS...High pressure will continue to build over the region. Moisture will gradually increase through the weekend into early next week. && .SHORT TERM (Through 12Z Sunday)...High pressure remains entrenched across the Pacific Northwest. An area of weak low pressure remains across central Arizona. Afternoon mesoanalysis reveals a moisture continuity across southern Utah, with dewpoints near 60F in the St. George area, decreasing to near 30F in the Bryce Canyon area. SBCAPE is currently near 1000-1500 J/kg across Washington and western Kane Counties (potentially closer to 2000 J/g+ near the Utah/Nevada/Arizona area). While deep layer shear is quite limited, storms are slowly transitioning down north/south drainages into the area of greater instability. Expect the potential for isolated flash flooding across portions of Washington and Kane Counties through early evening. Current highest threat areas are Kanab Creek, Johnson Wash and potentially the headwaters that eventually reaches Wire Pass. Those considering outdoor activities in these areas should consider altering their plans. Convection will gradually diminish this evening. Another round of convection is expected Friday afternoon and evening, with similar levels of instability. One difference is some of the guidance indicates deep layer shear may approach 20kts with a slight increase in mid-level flow. This may allow for somewhat stronger storms. The biggest threat will be across Iron, Washington, Kane and Garfield Counties. Additional convection will be possible across the higher terrain of central and northern Utah, though moisture won't be nearly as deep. A similar pattern is expected Saturday afternoon and evening. The current forecast keeps the highs at Salt Lake City Airport below 100F...but it's possible the area will overperform and we will add to the total of 100 degree days. .LONG TERM (After 12Z Sunday)...Sunday will see the end of our brief warming trend across the state, with temperatures trending cooler into the week as high pressure weakens and gives way to an incoming trough and increasing uncertainty in the forecast. A trough more reminiscent of autumn than August is represented across the suite of ensemble forecasts, though significant uncertainty exists in its progressive nature and amplitude. What can be said with confidence is that by Monday afternoon, moisture will increase across the region ahead of the trough, with the trough providing synoptic-scale lift enabling more organized convection for portions of the forecast area Monday through the middle of the week. As the clusters trend towards two distinct solutions, it is hard to pin down a most likely scenario, with one group congealing on a less- amplified and more progressive trough that would only brush northern Utah and southwest Wyoming and likely not advect as much moisture into our area. The other solution is a deeper trough with a long residence time, allowing for considerable and continued moisture transport into the region and periods of heavy rainfall. Southern Utah is favored in the majority of solutions, with slightly lower chances across east-central Utah and southwest Wyoming. However, there has been considerable variability from one cycle to the next, so caution should be used interpreting any trends. && .AVIATION...KSLC...Light northwest winds are forecast this afternoon and evening switching over to the southeast around 6Z later this evening. VFR ceiling and visibilities are expected with higher layer clouds expected. REST OF UTAH AND SOUTHWEST WYOMING...Vicinity showers and thunderstorms are forecast for CDC, BCE and SGU through this evening with a slight chance of this activity reaching the terminal. Outflow from these thunderstorms may reach the terminal as well. Otherwise, light winds can be expected throughout the period across the region. && .FIRE WEATHER...Thunderstorms have developed across portions of southwest Utah this afternoon and evening. Expect more coverage of these thunderstorms, spreading north and east along the higher terrain as far north as the Uintas Friday. The threat of showers and thunderstorms will continue through the weekend into early next week. Currently, there is a threat of increased winds early next week, but model consistency is quite low resulting in low confidence of any particular scenario at this time. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && Kruse/Wessler/NDeSmet 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
The Cedar City radar (KICX), 68 km away, was scanning. The volume nearest the first event began at 23:16 UTC.
1 flash flood, 1 hail. Local standard time, as filed.
Photos from broadcast media indicated water and mud over a roadway in Kanab.
A viewer submitted a video that showed quarter-sized hail.
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: 981957, 981958.