A moist airmass across Utah in the first week of August led to scattered thunderstorms producing heavy rain. These storms produced several flash floods, primarily across the southern half of 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.
A moist airmass across Utah in the first week of August led to scattered thunderstorms producing heavy rain. These storms produced several flash floods, primarily across the southern half of 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 3, 9:14 AM MST, 3 hours 46 minutes earlier.
Area Forecast Discussion National Weather Service Salt Lake City UT 1014 AM MDT Thu Aug 3 2017 .UPDATE...With dewpoints running about 5F higher across southern Utah compared to 24 hours ago, expect deeper instability later this afternoon with MUCAPE values approaching the 1000-1500 J/KG range by 2000 UTC. Elected to increase pops across southern Utah due to deeper instability and increased lift associated with a shortwave trough upstream near the ID/NV border. Will be keeping a close eye on southern Utah this afternoon for potential flash flooding concerns, given the better instability/moisture and down-drainage storm motion. Although LCL heights are on the higher side, mean steering flow out of the N-NW at 5 knots will favor thunderstorms moving slowly down drainage. && .SYNOPSIS...Strong high pressure aloft centered over the western Great Basin will remain the dominant feature for Utah through the balance of the week. Limited moisture will remain in place across the north, with deeper moisture across southern Utah. && .PREVIOUS DISCUSSION...An elongated ridge axis remains aligned from nrn CA to central NM early this morning with a generally dry nwly flow over most of our CWA. A weak disturbance sliding e-se out of nrn NV into nrn UT has generated some cloudiness and a few light showers on the TDWR radar. Do not expect more than light sprinkles from these this morning and have kept mentionable pops out of the forecast until this aftn. Convection should develop again across mainly central and srn UT this aftn with a potential for isolated heavy rain along and south of the ridge axis in the deeper moisture, basically from about Cedar City south. Slightly better instability should bring an uptick in the coverage from yesterday. Cannot rule out a weak cells over the Uinta mtns and Wasatch Plateau and left a small chance for that area too. Temps look to cool a little across the south today due to the slight increase in convection while the north stays warm again. Little change in this pattern is expected thru Fri altho the ridge axis could shift a little south. Deeper moisture should still hang along the AZ border due to the light flow with any threat of heavy rain staying in this area. The ridge over the Great Basin begins to weaken through the day Saturday, as a shortwave trough starts to push into California. Ahead of this trough, weak low- level southwesterly flow will help to bring some additional moisture into the area. Between the lower heights and increased cloud cover, Saturday will likely be a somewhat cooler day across much of the CWA, though the best convective activity should still remain across the southern half of Utah. Moisture continues to push northward through Saturday night and Sunday, with precipitable water values of at least 0.9 inches expected to make it up to about Ogden by 00Z Monday. There is some concern that Sunday will become too cloudy across the north to get great convection, so have kept the best POPs across the central and southern portions of the CWA. However, the cooling trend definitely looks to continue, with the forecast currently calling for about a 5 degree cool down from Saturday to Sunday across the north. There is chance even this cooling is not enough, as some MOS guidance has highs in the low-to-mid 80s across the Wasatch Front on Sunday. For the beginning of next work week, the high circulation re- establishes itself over southern Arizona, with a persistent west- southwest flow pushing some drier air into the southern portions of Utah. However, the airmass across northern and central Utah remains moist, and convective development will likely be aided by a series of weak disturbances sliding over the ridge and across the Great Basin. Have maintained elevated POPs across the northern half of the CWA for Monday and Tuesday, and these POPs will likely have to be increased in the future, especially when it gets close enough to potentially time the waves coming across the area. Temperatures for the first half of the week look to remain noticeably cooler than the relentless heat that dominated most of July. Heading into Wednesday and Thursday, models are in fairly good agreement about strengthening the shortwave trough sitting over California, and pushing the high center eastward to New Mexico and Texas. This could increase the dry southwesterly flow, allowing some of this drier air to start permeating into northern Utah and southwest Wyoming. Have kept a slow downward trend in POPs and very slow upward trend in temperatures for days 6 and 7. && .AVIATION...VFR conditions to continue at the SLC terminal today and tonight. Winds at the SLC terminal are expected to switch to the northwest around 17-19Z, then back to southeast around 03-05Z. && .FIRE WEATHER...A generally dry west to northwest flow will continue across the northern and central portions of the district. Local critical fire weather conditions are possible across the northern Wasatch Mountains again this afternoon and Friday as RH drops into the mid teens and breezy west to northwest winds develop each afternoon. Isolated weak thunderstorms are still possible over the Uintas southward across the Wasatch Plateau today and Friday. Storms over the south will be somewhat stronger and have a better chance of wetting rains. Moisture will spread northward this weekend bringing an increase in thunderstorm coverage to the north. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && UPDATE...Lukinbeal PUBLIC...Wilensky/Schoening AVIATION...Van Cleave FIRE WEATHER...Wilensky 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
Hazardous Weather Outlook National Weather Service Salt Lake City UT 503 AM MDT Thu Aug 3 2017 UTZ001>016-019>021-517-518-WYZ021-041200- Cache Valley/Utah Portion-Northern Wasatch Front- Salt Lake and Tooele Valleys-Southern Wasatch Front- Great Salt Lake Desert and Mountains-Wasatch Mountain Valleys- Wasatch Mountains I-80 North-Wasatch Mountains South of I-80- Western Uinta Mountains-Wasatch Plateau/Book Cliffs- Western Uinta Basin-Castle Country-San Rafael Swell- Sanpete/Sevier Valleys-West Central Utah-Southwest Utah- Utahs Dixie and Zion National Park-South Central Utah- Glen Canyon Recreation Area/Lake Powell-Central Mountains- Southern Mountains-Southwest Wyoming- 503 AM MDT Thu Aug 3 2017 This Hazardous Weather Outlook is for the western two thirds of Utah and southwest Wyoming. .DAY ONE...Today and Tonight Isolated showers and thunderstorms will fire up again today across the Uinta mountains and Wasatch Plateau. Scattered showers and thunderstorms are expected across the southern outlook area. Most of these will remain over the higher terrain and across extreme southern Utah. Locally heavy rains are possible with the showers and storms across the far south. .DAYS TWO THROUGH SEVEN...Friday through Wednesday The coverage of showers and storms will stay about the same on Friday with a continued chance of locally heavy rains across the far south. Thunderstorm coverage should increase this weekend and continue into early next week with the threat of heavy rainfall spreading across more of the outlook area> This will bring a risk of isolated flash flooding of slot canyons, dry washes and burn scars. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. For more information from NOAA/s National Weather Service visit... http://weather.gov/saltlakecity For information on potential road travel impacts visit... http://www.udottraffic.utah.gov/roadweatherforecast.aspx
The Cedar City radar (KICX), 169 km away, was scanning. The volume nearest the first event began at 19:57 UTC.
7 flash flood, 1 thunderstorm wind. Local standard time, as filed.
Flash flooding was reported in Capitol Reef National Park, with 4 to 6 inches of flowing water reported in Capitol Gorge. This water damaged the dirt road that provides access to the Capitol Gorge area.
A 62 mph wind gust was recorded at the Bullfrog Marina sensor.
Heavy rain over the Brianhead Fire burn scar caused flash flooding along State Routes 143 and 271, temporarily closing these routes due to debris on the roadways.
Heavy rain led to flash flooding across the southern half of Zion National Park, including along Pine Creek. In addition, street flooding was reported in the towns of Springdale and Rockville.
Heavy rain on the Brianhead Fire burn scar once again caused flooding and debris along State Route 143, this time near the White Bridge Campground in the Panguitch Creek Drainage. A front loader was needed to remove the boulders from the road.
Flash flooding was reported along Coyote Creek, which is a tributary of Wahweap Creek.
The Paria River rose from 7 cfs to 1240 cfs, or an increase of approximately 3 feet.
Multiple rounds of heavy rain over the Brianhead Fire burn scar produced both flash flooding and debris flows. This debris and water first inundated State Route 143, ultimately closing portions of the roadway for multiple days. A second round of rain in the early evening hours flowed into Parowan Creek and ran into the town of Parowan, with water 6-8 feet above normal stage during the event. This later flooding damaged four homes in Parowan, primarily basements. In addition, flood damage occurred along Old United States Highway 91, as well as northbound lanes of Interstate 15 between milepost 73 and Parowan. The debris field along Interstate 15 was approximately an eighth of a mile long, and forced the closure of the roadway for several hours.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Utah in 2017Every state in 2017This day in weather historyWarnings in Utah, August 2017
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: 719014, 718998, 720698, 719017, 720705, 719018, 719019, 720708.