Very efficient thermal profiles with a deep warm cloud layer allowed thunderstorms to produce heavy rainfall during the mid-afternoon hours. Gauge reports from one to two inches of rain were common over the urban center of Sioux City, most of which fell within an hour.
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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 FSD wrote it up.
Very efficient thermal profiles with a deep warm cloud layer allowed thunderstorms to produce heavy rainfall during the mid-afternoon hours. Gauge reports from one to two inches of rain were common over the urban center of Sioux City, most of which fell within an hour.
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 Sioux Falls, SD wrote its last area forecast discussion before the first event at Aug 29, 2:17 PM CST, 1 hour 13 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Sioux Falls SD 317 PM CDT Thu Aug 29 2024 .KEY MESSAGES... - Scattered showers and storms remain possible through sunset, a few of which could become strong to severe, especially in areas east of I-29. Primary hazards include quarter size hail, gusts up to 60 mph, brief heavy downpours, and frequent lightning. - Dry conditions expected to prevail for the remainder of the forecast period, with notably cooler temperatures in store Sunday and Monday. && .DISCUSSION... Issued at 316 PM CDT Thu Aug 29 2024 Latest radar imagery shows scattered showers and storms ongoing across the region ahead of an advancing cold front. Have already noted clearing in areas west of the James River, which should continue to spread eastward through the afternoon as the aforementioned cold front departs the region. While SPC's latest Day 1 Outlook does maintain a Slight (Level 2 of 5) and Marginal (Level 1of 5) Risk for our area, believe our chances of seeing any strong to severe storms have somewhat weakened. This is in part because convection started much earlier than anticipated, along with decent stabilization from ample cloud cover. Bulk layer shear also remains somewhat meager (~25kts), with mid-level lapse rates near 6-6.6 degC/km. Thus, think if any storm were to become strong to severe, believe quarter size hail and gusts up to 60 MPH would now be the primary hazards, especially in areas east of I-29. Outside of this, could also see brief heavy downpours and frequent lightning. Should see convection gradually diminish through the early evening, with most CAMs showing dry conditions returning across the region near/shortly after sunset. As alluded to in the previous discussion, expect afternoon highs to be a touch cooler tomorrow, with temperatures mainly in the upper 70s to lower 80s. Winds during this time will also remain light under mostly sunny skies, which should make for quite the pleasant day across the region. Sfc high pressure builds overhead Saturday, with winds shifting to the south/southwest. Thus, with a bit of WAA will see highs once again rise into the lower 80s to lower 90s. Moisture starved cold front dives southeastward across the central CONUS Saturday night, bringing notably cooler temperatures back to the region Sunday. Currently have afternoon highs rising into the low to mid 70s under mostly sunny skies, with overnight lows falling into the upper 40s to lower 50s - a refreshingly cool start to September. Expect much of the same Monday in terms of temperatures, with southerly winds capable of gusting between 20 to 30 MPH along and west of I-29 through the afternoon. Otherwise, look for quiet conditions to prevail for the remainder of the forecast period as upper level ridging builds overhead. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1236 PM CDT Thu Aug 29 2024 Scattered showers and storms continue push eastward across the region ahead of an advancing cold front. A few storms may become strong to severe this afternoon, and capable of producing large hail, damaging winds, and frequent lightning. May also see cigs/vsbys briefly fall to MVFR levels. That being said, should see activity quickly diminish across the region near/after 00z. Otherwise, look for quiet conditions to prevail for the remainder of the period, with winds gradually turning northwesterly in the wake of FROPA. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && DISCUSSION...SST AVIATION...SST
Hazardous Weather Outlook National Weather Service Sioux Falls SD 404 AM CDT Thu Aug 29 2024 IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097- 098-NEZ013-014-SDZ038>040-050-052>071-300915- Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Lincoln-Murray-Cottonwood-Nobles-Jackson- Pipestone-Rock-Dixon-Dakota-Beadle-Kingsbury-Brookings-Gregory- Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-McCook- Minnehaha-Charles Mix-Douglas-Hutchinson-Turner-Bon Homme-Yankton- Union- 404 AM CDT Thu Aug 29 2024 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska, central South Dakota, east central South Dakota, south central South Dakota and southeast South Dakota. .DAY ONE...Today and tonight. Scattered thunderstorms are expected to develop throughout the morning hours, possibly becoming severe for areas along and east of a line from Marshall, MN to Sioux City, IA. Strong wind gusts to 70 mph and golf ball sized hail are the main threats, though an isolated tornado cannot be ruled out. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Hazardous weather is not expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
Preliminary Local Storm Report
National Weather Service Sioux Falls SD
341 PM CDT Thu Aug 29 2024
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0225 PM Hail 4 N Round Lake 43.60N 95.47W
08/29/2024 E1.00 Inch Nobles MN Emergency Mngr
&&
TRMThe Sioux Falls radar (KFSD), 121 km away, was scanning. The volume nearest the first event began at 21:28 UTC.
1 flash flood. Local standard time, as filed.
Water was flowing 7 to 8 inches deep across roadways, disrupting travel.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2024Every state in 2024This day in weather historyWarnings in Iowa, August 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: 1206192.