Event Summary May 21, 2024 Tornadoes, Winds and Flash Flooding

Tornadoes

Tornado #3 - Polk/Story Tornado Polk into Story Counties Date 5/21/2024 Time (Local) 4:30 pm-5:05 pm EF Rating EF-2 Est. Peak Winds 135 mph Path Length 41.14 miles Max Width 1000 yds Injuries/Deaths 4/0   Track Map Downloadable KMZ File

Tornado #4 - SE Adams Tornado Adams County Date 5/21/2024 Time (Local) 3:18-3:36pm EF Rating EF-1 Est. Peak Winds 95 mph Path Length ~12.8 miles Max Width 200 yds Injuries/Deaths 0/0 Damage assessments in southeast Adams county have been completed, identifying damage consistent with an EF1 tornado. Track Map Downloadable KMZ File

Tornado #5 - Exira Tornado Audubon County Date 5/21/2024 Time (Local) 3:09pm-3:18pm EF Rating EF-1 Est. Peak Winds 95 mph Path Length 7.33 miles Max Width 100 yards Injuries/Deaths None   Track Map Downloadable KMZ File

Tornado #6 - Arbor Hill Tornado Adair County Date 5/21/2024 Time (Local) 3:41pm-3:56pm  EF Rating EF-2 Est. Peak Winds 115 mph Path Length 11.87 miles Max Width 200 yards Injuries/Deaths None As the Greenfield tornado began to dissipate northeast of Greenfield, the storm cycled producing this tornado which extended into northeast Adair County. Track Map Downloadable KMZ File

Tornado - #7 - Martensdale Tornado Warren County Date 5/21/2024 Time (Local) 4:25pm-4:26pm EF Rating EF-0 Est. Peak Winds 75 mph Path Length 1.04 miles Max Width 40 yards Injuries/Deaths None Trees Downed in and near Martensdale. TDS was observed on radar verifying the tornado. Track Map Downloadable KMZ File

Tornado #8 - Spring Hill Tornado Warren County Date 5/21/2024 Time (Local) 4:28pm-4:32pm EF Rating EF-0 Est. Peak Winds 75 mph Path Length 2.01 miles Max Width 75 yards Injuries/Deaths None Trees Down in and around Spring Hill. TDS observed on radar to verify the tornado. Track Map Downloadable KMZ File

Tornado #9 - Macksburg Union into Madison Counties Date 5/21/2024 Time (Local) 3:50pm-3:54pm EF Rating EF-0 Est. Peak Winds 70 mph Path Length 3.98 miles Max Width 70 yards Injuries/Deaths 0/0   Track Map Downloadable KMZ File

Tornado - LOCATION COUNTY NAME Date   Time (Local)   EF Rating   Est. Peak Winds   Path Length   Max Width   Injuries/Deaths   Summary: Short summary of the tornado. Track Map Downloadable KMZ File

The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:

EF0 Weak 65-85 mph	EF1 Moderate 86-110 mph	EF2 Significant 111-135 mph	EF3 Severe 136-165 mph	EF4 Extreme 166-200 mph	EF5 Catastrophic 200+ mph

Hail & Wind Damage:

1.5 inch hail in Creston between 430 and 440pm. Photo credit: Brad Fogle	Large tree down from strong winds in Hanlontown around 5:50 pm. Photo credit: Lisa Schaefer

Flooding

Significant flash flooding occurred across portions of central Iowa on the morning of May 21, 2024 impacting several communities including Kellogg and Baxter. Flash flooding threatened the water treatment and drinking water supply in Kellogg with sandbagging taking place. Numerous homes and other buildings were also flooded in town with evacuations. Sandbagging also took place in Baxter due to flooding, which threatened homes and other buildings. Some evacuations also took place. Car water rescues due to flash flooding were reported by the Meskwaki Nation Police Department with landslides reported in Marshall County affecting some roads. All told across central Iowa, there were approximately 75-100 road closures from local, county, state and federal roads with some road washouts, mainly on gravel, due to the swiftly moving flood waters.

Hydrographs

Iowa River near Tama	South Skunk River at Colfax	East Fork Des Moines River at Algona	Cedar River at Cedar Falls

Photos and Rainfall Reports

Near Rock Creek State Park, May 21, 2024 around 830am Photo: Emma Fox	Radar estimated rainfall showing totals of 4-6 inches over Jasper and parts of Marshall, Tama, Poweshiek, Hardin, Grundy, and Black Hawk counties from May 19, 2024 at 7am until May 21, 2024 at 7pm.	CoCoRaHS rainfall reports May 20-22, 2024. Interactive Map	Zoomed in CoCoRaHS rainfall reports over portions of central Iowa May 20-22, 2024 Interactive Map

Near Rock Creek State Park, May 21, 2024 around 830am Photo: Emma Fox	Water over Highway 14 north of Marshalltown. Photo: Joe Price	Flood water at the Marshalltown Water Works. Photo: Joe Price

Rain Reports

Rainfall reports prior to the arrival of the afternoon storms on May 21st, 2024. 

Public Information Statement
National Weather Service Des Moines IA
125 PM CDT Tue May 21 2024

...PRECIPITATION REPORTS...

Location                     Amount    Time/Date
Algona                       5.08 in   0700 AM 05/21
Parkersburg                  4.74 in   0108 PM 05/21
Algona                       4.14 in   0115 PM 05/21
Pocahontas 0.5 W             4.02 in   0808 AM 05/21
Algona                       3.81 in   0119 PM 05/21
Algona 2.5 S                 3.60 in   0700 AM 05/21
Pocahontas                   3.41 in   0800 AM 05/21
3 N Toledo                   3.33 in   0700 AM 05/21
Audubon                      3.30 in   0800 AM 05/21
Ankeny                       3.27 in   0109 PM 05/21
Manning 0.2 ESE              3.18 in   0700 AM 05/21
Guthrie Center               3.12 in   0700 AM 05/21
Traer                        3.09 in   0700 AM 05/21
Garwin                       3.05 in   0600 AM 05/21
Britt 8.2 NNW                2.98 in   0700 AM 05/21
Nevada 4.6 S                 2.95 in   0700 AM 05/21
Pocahontas                   2.90 in   0110 PM 05/21
Maxwell 2.5 N                2.90 in   0700 AM 05/21
Vining 0.2 ENE               2.90 in   0700 AM 05/21
Iowa Falls                   2.90 in   0700 AM 05/21
Liscomb                      2.88 in   0115 PM 05/21
Ankeny 2.3 NE                2.75 in   0700 AM 05/21
Iowa Falls Airport           2.72 in   0115 PM 05/21
Gilbertville 1.0 NW          2.68 in   0800 AM 05/21
Polk City 0.4 W              2.65 in   0700 AM 05/21
Audubon Airport              2.65 in   0115 PM 05/21
Waterloo Airport             2.65 in   1254 PM 05/21
Perry                        2.62 in   0115 PM 05/21
4 SSW Waterloo               2.62 in   0115 PM 05/21
Polk City 0.8 W              2.61 in   0700 AM 05/21
Malcom 7.7 NNW               2.61 in   0700 AM 05/21
0.7 SW Tama                  2.59 in   0100 PM 05/21
Madrid                       2.57 in   0106 PM 05/21
0.7 NW Toledo                2.53 in   0100 PM 05/21
Grinnell 0.6 NW              2.50 in   1100 AM 05/21
Johnston 3.7 NNW             2.44 in   0700 AM 05/21
Bondurant 1.0 NE             2.40 in   0627 AM 05/21
3 NNW Pleasant Hill          2.37 in   1259 PM 05/21
Ankeny 1.5 NNE               2.35 in   0700 AM 05/21
Polk City 1.0 N              2.34 in   0700 AM 05/21
Ankeny 2.4 NW                2.28 in   0700 AM 05/21
Big Creek Ponding            2.25 in   1215 PM 05/21
Ankeny 3.3 ESE               2.24 in   0700 AM 05/21
NEAL SMITH NWR DES MOINES 17 2.24 in   0110 PM 05/21
New Providence               2.22 in   0100 PM 05/21
Mallard                      2.20 in   0100 PM 05/21
Iowa Falls 4.6 NNE           2.20 in   0646 AM 05/21
Perry Airport                2.20 in   1255 PM 05/21
Beaman                       2.18 in   0109 PM 05/21
1 NE Johnston                2.16 in   0116 PM 05/21
Hudson 1.1 SSE               2.15 in   0700 AM 05/21
Marshalltown                 2.07 in   0120 PM 05/21
Jefferson 0.1 ENE            2.05 in   0900 AM 05/21
Fonda 4.5 NNW                2.04 in   0800 AM 05/21
Marshalltown 0.2 WSW         2.03 in   0803 AM 05/21
Eldora                       2.01 in   0100 PM 05/21

Observations are collected from a variety of sources with varying
equipment and exposures. We thank all volunteer weather observers
for their dedication. Not all data listed are considered official.

Photos & Video

South of Greenfield. (Photo Credit: Adam Orgler)	Carbon to Morton Mills tornado (Photo Credit: David Baxter)	Corning tornado (Photo Credit: Colt Forney)	Wind turbine destroyed by tornado (Photo Credit: Colt Forney)

Header

Caption (source)	Caption (source)	Caption (source)	Caption (source)

Radar & Satellite

Full radar loop with warnings courtesy of the Iowa Environmental Mesonet.

Des Moines Radar Images

Each image below shows the 0.5 degree tilt (unless otherwise noted) of reflectivity (top left), correlation coefficient (top right), base velocity (bottom left), and storm relative velocity (bottom right). In the velocity images, where a warm color meets a cool color, such as red and green, this is the radar signature of rotation. Blue in the correlation coefficient is debris from the tornado, though not all images below show this feature.

Radar as tornado nears Greenfield	Radar of tornado near Carbon	Radar 0.9 degree tilt of tornado between Polk City and Ankeny as it tracks northeast	Radar as tornado tracks near Prescott

Radar of tornado near Exira	Radar as tornado passes close to Arbor Hill	Radar as tornado moves through Martensdale	Radar as tornado passes Spring Hill

1 minute visible satellite imagery from GOES-East as severe storms moved across Iowa on the afternoon and early evening of May 21, 2024

Blog Posts

Tornado Damage in Greenfield - NASA Earth Observatory

Storm Reports

Interactive Storm Report Map (Iowa Mesonet)

Environment

Figure 1: 925 mb map loop from 1pm (18z)  to 7pm (00z) May 21st.	Figure 2: 0-6 km shear map loop from 1pm (18z)  to 7pm (00z) May 21st.	Figure 3: Surface-based CAPE map loop from 1pm (18z)  to 7pm (00z) May 21st.

Figure 4: 0-1 km storm relative helicity map loop from 1pm (18z)  to 7pm (00z) May 21st.	Figure 5: Significant Tornado Parameter (STP) map loop from 1pm (18z)  to 7pm (00z) May 21st.	Figure 6: 0-3 km MLCAPE and surface vorticity map loop from 1pm (18z)  to 7pm (00z) May 21st.