After a line of storms producing damaging winds and tornadoes passed across the area in the morning, a second wave passed over the area. The wave lacked strong forcing and present weak instability, but deep layer shear was high.
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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 DMX wrote it up.
After a line of storms producing damaging winds and tornadoes passed across the area in the morning, a second wave passed over the area. The wave lacked strong forcing and present weak instability, but deep layer shear was high. At the same time, moisture fueling storm development did not make it closer to the surface and low levels were dry. This allowed for rapid evaporative cooling as precipitation fell, producing gusty winds with what appeared as rather weak storms on radar.
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 Des Moines, IA wrote its last area forecast discussion before the first event at May 7, 2:43 PM CST, 2 hours 43 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Des Moines IA 343 PM CDT Tue May 7 2024 .KEY MESSAGES... - Scattered showers & storms possible into the night - Chances for showers and storms Wednesday into Thursday. Potential low overall, but severe weather still possible late Wednesday. - Less active to end the week and into early next week with normal to above normal temperatures && .DISCUSSION... Issued at 343 PM CDT Tue May 7 2024 Isolated showers and storms have begun to develop in daytime heating, a few with the lingering theta-e axis far east, and others higher based in the drier air west associated with approaching weaker mid level forcing, which will continue spotty chances into the early morning hours Wednesday. Otherwise, the sprawling parent upper level low will move little into tomorrow and induce a weak surface reflection/inverted trough into western Iowa during peak heating, which will also be aided by a lobe of the aforementioned increase in mid level kinematic forcing. The storm environment is interesting and somewhat nebulous with weak low level shear 1km and below, but strong deep 6-8km shear and extremely elongated hodographs aloft along a sharp north to south gradient (much higher south). While the 500-1500 J/kg MLCAPEs are not alarming, steep low level lapse rates are a good percentage of that (200+ J/kg 0-3km CAPE) with strong shallow updraft stretching potential. This parameter space leads to multiple hazardous weather concerns during the afternoon and evening hours. Even though low level kinematics such as shear and streamwise vorticity are weak, thermodynamically dominate funnels/weak tornado potential is there along and ahead of the inverted surface trough in what will likely be sub-1km LCLs. This would be more favorable with discrete cells farther south realizing the deeper shear and taking on the much slower Bunkers RM motion (<20kts) versus a strong 30-40kt mean wind. Some 2-5km updraft helicity tracks are evident in the 12Z HREF as well, supporting supercell potential coincident with the noted thermodynamics, and there is also some signal in AI/Nadocast guidance. Weak low level shear under much stronger deep shear and elongated hodographs would also be favorable for hail production. Going into the early evening, the stronger mean wind should subside as the upper low is finally on the move and approaches leading to slower cell movement. Although the moisture parameters are fairly season, this slow movement could also lead to locally heavy rains with HREF PMM QPF suggesting isolated 2-4” amounts are possible north. Looking into Thursday, Low level focus and overall synoptic scale lift is weaker, however moisture lingering in the trailing cyclonic flow will lead to at least some chances for showers and a few storms through the day. A strong Upper MS Valley short wave, whose primary response will remain to our northeast, will start a period of relatively inactive northwest flow aloft until the pattern breaks down early next week with little model agreement on how that will unfold. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1247 PM CDT Tue May 7 2024 Patchy MVFR ceilings may linger east for the next few hours, but overall confidence is medium for VFR conditions through much of the period. There may be a period of higher based convection late afternoon and this evening, but otherwise nothing more than FEW-BKN mid clouds can be anticipated through the period. && .DMX WATCHES/WARNINGS/ADVISORIES...None. && DISCUSSION...Small AVIATION...Small
Hazardous Weather Outlook National Weather Service Des Moines IA 349 PM CDT Tue May 7 2024 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-082100- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun- Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene- Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper- Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union- Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne- Appanoose-Davis- 349 PM CDT Tue May 7 2024 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...This afternoon and tonight Isolated non-severe thunderstorms are possible at times tonight. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Scattered thunderstorms are forecast Wednesday afternoon into Wednesday night. A few storms could produce hail or gusty winds, with funnel clouds or a few weak tornadoes also possible. However, the overall severe weather threat is marginal (1 out of 5). There will be a renewed chance for locally heavy rainfall, however, especially north. Thunderstorms will also be possible at times on Thursday and Friday though severe weather is not anticipated at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not needed tonight.
Special Weather Statement National Weather Service Des Moines IA 549 PM CDT Tue May 7 2024 IAZ004>006-015-016-023>025-033>036-044>048-057>060-070>073- 081>083-092>094-080200- Emmet-Kossuth-Winnebago-Palo Alto-Hancock-Pocahontas-Humboldt- Wright-Sac-Calhoun-Webster-Hamilton-Crawford-Carroll-Greene-Boone- Story-Audubon-Guthrie-Dallas-Polk-Cass-Adair-Madison-Warren-Adams- Union-Clarke-Taylor-Ringgold-Decatur- Including the cities of Estherville, Algona, Forest City, Lake Mills, Emmetsburg, Garner, Britt, Kanawha, Pocahontas, Laurens, Rolfe, Fonda, Gilmore City, Humboldt, Eagle Grove, Clarion, Belmond, Sac City, Lake View, Odebolt, Wall Lake, Schaller, Early, Rockwell City, Manson, Lake City, Pomeroy, Fort Dodge, Webster City, Denison, Carroll, Jefferson, Boone, Ames, Audubon, Exira, Guthrie Center, Panora, Bayard, Casey, Perry, Waukee, Adel, Des Moines, Atlantic, Greenfield, Stuart, Adair, Fontanelle, Winterset, Earlham, Indianola, Norwalk, Carlisle, Corning, Creston, Osceola, Bedford, Lenox, New Market, Mount Ayr, Lamoni, and Leon 549 PM CDT Tue May 7 2024 ...Gusty Winds up to 50 mph Possible with Light Rain and Rain Showers... As showers continue to develop and move across the area, brief gusty winds up to and in excess of 40 mph may be experienced. These are being driven by evaporative cooling as rain falls through very dry air below it. These wind gusts are likely to continue until shower activity begins to subside later this evening. CURTIS
The Des Moines radar (KDMX), 7 km away, was scanning. The volume nearest the first event began at 23:25 UTC.
8 thunderstorm wind. Local standard time, as filed.
Large tree branch down. Image from social media and time estimated by radar.
Snapped Tree branches, roughly 4 to 5 inches in diameter.
Large tree down in Polk City. Time estimated by radar.
Multiple tree limbs down, the largest was approximately 6 inches in diameter.
Large branch down. Time estimated by radar.
Large limb from healthy tree snapped off and blocking the roadway. Time estimated by radar.
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, May 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: 1182935, 1182936, 1182938, 1182939, 1182940, 1182941, 1182943, 1182945.