Stagnant conditions south of a stalled frontal boundary across North Dakota and central Minnesota led to high dew points and very warm conditions across the region. Afternoon and early evening heat index values varied from 100 to 110 degrees each afternoon.
Every event with a place to put it; 11 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 FSD wrote it up.
Stagnant conditions south of a stalled frontal boundary across North Dakota and central Minnesota led to high dew points and very warm conditions across the region. Afternoon and early evening heat index values varied from 100 to 110 degrees each afternoon.
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 2, 11:08 AM CST, 52 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Sioux Falls SD 1208 PM CDT Fri Aug 2 2024 .KEY MESSAGES... - Hot today and Saturday with highs in the 90s most locations. Afternoon heat indices will be in the mid to upper 90s. Roughly a 40 percent chance for heat advisory criteria which would be heat indices at or above 100 degrees for at least 3 hours. Better chance on Saturday. - Isolated storms will be possible Saturday night along highway 14 and into parts of southwest MN. A very isolated severe storm will be possible. - A bit better chance for thunderstorms later Sunday night into Monday morning with isolated to scattered severe storms possible. Better chance north of I-90. - Below normal temperatures next week, especially Tuesday into Friday. && .DISCUSSION... Issued at 236 AM CDT Fri Aug 2 2024 Patchy early morning fog will be possible, but should only cause minor impacts. A ridge of high pressure at the surface will be in place today. This will lead to a warm day with lighter winds with most locations climbing into the 90s. Humidity levels will remain more typical for summer with dew points in the 60s. With this ridge of high pressure in place tonight, temperatures will fall back into the lower to mid 60s, but with some southerly flow developing in central SD, temperatures may only drop into the upper 60s there. An upper level northwest oriented jet streak will increase across the Northern Plains Saturday into Saturday night. This will aid in producing very warm temperatures but with a bit of a westerly push the low level inversion should be much weaker which will help keep the oppressive dew points from developing. Regardless highs in the 90s for most of the area and some readings close to 100 in central SD. Upper level support and an associated low level cold front will move into northern SD by late afternoon and will likely be the focus for scattered thunderstorms. Model soundings suggest that southeast SD will remain capped so for now convection before about 10 pm looks pretty unlikely. As this wave tracks into MN, the axis of instability and mid level warm nose drops towards highway 14. This could bring some isolated activity but confidence is pretty low at this time, so for now aiming for lower chances Saturday night into Sunday morning mainly north of I-90. What this wave appears to do is drop a west to east oriented low level front into the area which should serve as a focus for thunderstorms Sunday night into Monday as a stronger wave approaches from the northwest. Low to mid level warm advection really cranks up around midnight Sunday night and locks into place near and north of I-90 through at least Monday morning. Still a lot of question marks that far out but current model trends suggest that any parcel ascent below about 800-850mb will be capped which could leave the better chances for showers and thunderstorm just north of highway 14. Decent directional shear from 850mb to 500mb and CAPE roughly running 1500 J/kg so some isolated to scattered severe storms will be possible. With inflow into the updraft likely directed from the southwest and northwest flow aloft storm motion should be mostly easterly to southeast if storms strengthen and tap into the lower level instability/forcing. Monday remains a question mark as the timing of this stronger wave may allow for some warmer readings across the area. Faster wave, cooler temperatures, slower wave warmer temperatures, so a lower confidence higher spread temperatures scenario for Monday. The remainder of the week should see mostly below normal temperatures and periodic chances for showers and thunderstorms as an active northern stream upper level jet keeps bringing reinforcing shots of cooler air. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1206 PM CDT Fri Aug 2 2024 VFR conditions will prevail through the period. Patchy fog is possible Saturday morning east of the I-29 corridor. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && DISCUSSION...08 AVIATION...BP
Hazardous Weather Outlook National Weather Service Sioux Falls SD 718 AM CDT Fri Aug 2 2024 IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097- 098-NEZ013-014-SDZ038>040-050-052>071-031230- 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- 718 AM CDT Fri Aug 2 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. The probability for widespread hazardous weather is low. Afternoon heat indices will reach 90 to 100 degrees this afternoon through early evening. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. Heat indices will again reach 90 to 100 degrees on Saturday afternoon. Isolated thunderstorms will be possible near highway 14 and into parts of southwest Minnesota Saturday night. Cannot rule out an isolated strong to severe storm or two. Sunday night into Monday morning will see scattered thunderstorms mainly north of I-90. A few of these storms could become severe. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
The national radar mosaic for the moment the first event began.
11 heat. Local standard time, as filed.
Two-day heat index values peaked very briefly at 109 degrees at personal weather stations south of Ellsworth and near George, 103 degrees near Inwood, and 101 degrees near Larchwood.
Two-day heat index values peaked very briefly at 108 degrees at a personal weather station near Hartley, as well as 103 degrees at Ashton, and 102 degrees at a Iowa Road Weather Information System site near Sibley.
Two-day heat index values peaked very briefly at 107 degrees at a personal weather station near Milford and 101 degrees in Terril and Spirit Lake.
Two-day heat index values peaked at 103 degrees at personal weather stations near Hawarden and Hull, 102 degrees in Sioux Center, and 100 degrees at the Automated Weather Observing System site near Maurice.
Two-day heat index values peaked very briefly at 107 degrees at a personal weather station near Hartley and 100 degrees at the Automated Weather Observing System site near Sheldon.
Two-day heat index values peaked at 100 degrees at a Iowa Road Weather Information System site near Spencer.
Two-day heat index values peaked very briefly at 106 degrees at a personal weather in the northern portions of Sioux City, 102 degrees at the RAWS site near Westfield, and 100 degrees at the Automated Weather Observing System site in Le Mars.
Two-day heat index values peaked at 102 degrees at a personal weather station near Marcus.
Two-day heat index values peaked very briefly at 105 degrees at a personal weather station near Alta, as well as 102 degrees at a Iowa Road Weather Information System site near Rembrandt and 100 degrees at a personal weather station near Storm Lake.
Two-day heat index values peaked very briefly at 105 degrees at a personal weather station near Battle Creek and 101 degrees at a Iowa Road Weather Information System site near Ida Grove.
Two-day heat index values peaked at 104 degrees at the Iowa Road Weather Information System site near Moville and 100 degrees at the Automated Surface Observing System site in Sergeant Bluff.
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: 1214701, 1214702, 1214705, 1214706, 1214707, 1214708, 1214723, 1214728, 1214729, 1214730, 1214732.