Flash Flooding and Hail in Iowa, July 17 to 18, 2010

Name: Flash Flooding and Hail in Iowa, July 17 to 18, 2010
Start: 2010-07-17T22:10
End: 2010-07-18T08:43
Location: Iowa

July 17 to 18, 2010 · NWS DMX · 68 events in 18 counties and zones

A very unstable airmass was in place over Iowa as a cold front approached from the west. High temperatures the previous day were in the upper 80s and 90s for the most part, with 101 at Fairfield.

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: $3.1 million
Crop damage: $840,000
Events: 68

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.

What happened

The episode as NWS DMX wrote it up.

A very unstable airmass was in place over Iowa as a cold front approached from the west. High temperatures the previous day were in the upper 80s and 90s for the most part, with 101 at Fairfield. Dewpoint readings were in the 70s east to near 80 over the west. CAPE was in the 4000 to 5000 J/kg range with lifted indices of -8 to -11 C. Downdraft CAPE was quite high, 1200-1400 J/kg. CAPE in the -10 to -30 C layer of the atmosphere was between 300 and 500 J/kg. The atmosphere was quite strongly sheared with 45 to 60 kts of shear. Precipitable water was low, only 1 to 1.5 inches. With the relatively dry air, the LCL was between 1500 and 2500 meters. The airmass was also quite warm with the freezing level around 15,600 feet. Thunderstorms formed in two clusters. One extended from Minnesota southwest into eastern South Dakota. The other area was over central Nebraska. The convective area from South Dakota dropped southeast into Iowa during the late evening hours. It produced high winds and hail as it did. Hail was not the major mode of severe weather. Most of the larger hail occurred during the early stages of the storm. Golf ball size hail fell west of Graettinger in Palo Alto County for the largest hail report. The cluster of storms organized into a small derecho as it approached Fort Dodge. The derecho raced southeast through the Des Moines area and into southeast Iowa. It produced some hail as it did, but by in large high winds were the primary threat. Winds of 60 to 75 MPH were common, causing considerable tree damage. High winds of 65 to 75 MPH roared through Ames. A shelter at the Iowa State Veterinary Medicine School was blown over. Several horses were injured by the collapse. University officials has to euthanize one horse due to severe injuries. A measured wind gust of 84 MPH was recorded on the northwest side of the Des Moines Metro area. Power was knocked out to nearly 40,000 customers in central Iowa by the storms. Damage reports from along the path of the derecho were widespread. Grain bins were destroyed as well as numerous out buildings. Tree and power line damage was extensive all the way from the Minnesota border through south central Iowa. Heavy rain was also an issue with the storms. Rainfall of 1 to 2 inches per hour fell with the storms from Fort Dodge into the Des Moines area. Flash flooding was reported in Marion County. Heavy rainfall of 2 to 4 inches in under 2 hours flooded city streets in Knoxville, some 4 feet deep, with cars stalled in city streets. Water was also over the road southeast of Melcher-Dallas in Marion County. Flash flooding was reported in Webster City. Flooding blew manhole covers off and stalled several cars in the city. As the storm moved through the Raymond area of Black Hawk County, lightning struck a house. It blew a basketball size hole in the roof and caused electrical damage to the house and some structural damage to ceilings.

What forecasters said that day

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 Jul 17, 6:06 PM CST, 4 hours 4 minutes earlier.

Area forecast discussion, Jul 17, 6:06 PM CST, 4 hours 4 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
706 PM CDT SAT JUL 17 2010

.UPDATE AVIATION DISCUSSION 18/00Z.

.SHORT TERM /TONIGHT/...
CONVECTION ASSOCIATED WITH SHORTWAVE MOVING ACRS THE NORTHERN US
WILL BE MAIN CONCERN OVERNIGHT. INSTABILITY AXIS EXISTS FROM WESTERN
IA INTO THE BIG SIOUX VALLEY OF SOUTH DAKOTA. CONVECTION HAS BEEN
ONGOING IN THE WAA AND THETA-E ADVECTION AREA TO THE EAST OF THIS
AXIS THIS AFTERNOON. HRRR/SPC NMM WRF/NAM ALL INDICATE THAT THE
CONVECTION WILL DIVE SOUTH SOUTHEAST THIS EVENING AND OVERNIGHT INTO
IA. GIVEN THE BULK SHEAR AND INSTABILITY...APPEARS THAT A FORWARD
PROPAGATING MCS WIND MAKER IS IN STORE FOR THE NIGHT TIME WITH
DAMAGING WINDS EXPECTED. FORWARD MOVING CORFIDI VECTORS WOULD
INDICATE SPEEDS OF 50 TO 60KTS IN SYSTEM MOVEMENT BUT MAY NOT BE FAR
ENOUGH TO THE RIGHT. HAVE INCREASED POPS FARTHER SOUTH AND WEST
GIVEN THE LATEST MESOSCALE MODEL RUNS AND WILL CONTINUED THE SEVERE
WORDING. HEAVY RAINS REMAIN A POSSIBILITY AS WELL BUT THE QUICK
PROPAGATION SHOULD LIMIT OVERALL AMOUNTS.

.LONG TERM.../TONIGHT THROUGH SATURDAY/
HAVE MAINTAINED CHANCE POPS ACROSS ABOUT OUR SOUTHERN HALF SUNDAY
MORNING TAPERING FURTHER SOUTH IN THE AFTERNOON TO ACCOUNT FOR
DEPARTING MORNING CONVECTION FROM OVERNIGHT STORMS AS DISCUSSED
ABOVE...AS WELL AS POSSIBLE LINGERING PRECIP ASSOCIATED WITH THE
FRONTAL BOUNDARY STALLING JUST TO OUR SOUTH. THEREAFTER...A BRIEF
PERIOD OF SURFACE RIDGING SHOULD PROVIDE A RELATIVELY QUIET SUNDAY
NIGHT HOWEVER WE WILL REMAIN IN AN ACTIVE AND WET PATTERN THROUGH AT
LEAST THE FIRST HALF OF THE WEEK. AT 500 WE WILL REMAIN SANDWICHED
ON THE PERIPHERIES OF RIDGING TO OUR SOUTH AND FASTER WESTERLIES TO
OUR NORTH. WITHIN THIS REGIME THERE IS GENERAL AGREEMENT AMONG THE
MODELS THAT THE STALLED FRONTAL BOUNDARY OVER MISSOURI LATE SUNDAY
WILL PROGRESS NORTHWARD SOMEWHAT WITH THE RIDGING...DRAPING
SOMEWHERE ACROSS OUR AREA AND REMAINING STALLED NEARBY AT LEAST
THROUGH WEDNESDAY. MEANWHILE...MOISTURE AND WARM AIR ADVECTION SOUTH
OF THE BOUNDARY WILL CONTINUE TO PROVIDE INSTABILITY AS THE DECAYING
BOUNDARY PROVIDES A FOCUS MECHANISM AND SUBTLE SHORTWAVES RIDING THE
WESTERLIES ALOFT PROVIDE PERIODS OF LIFT FOR ADDITIONAL THUNDERSTORM
DEVELOPMENT. WITH THE SUBTLETIES OF THE BOUNDARY LOCATION AND ITS
INTERACTION WITH CONVECTIVE OUTFLOWS IT IS DIFFICULT TO PIN DOWN THE
AREAS OF HIGHEST POPS IN ANY GIVEN PERIOD...AND HAVE GONE WITH
BLANKET LOW TO MID RANGE CHANCE POPS FROM MONDAY THROUGH WEDNESDAY.
IT IS LIKELY THAT THE MOST LIKELY TIMES FOR RAIN/STORMS WILL BE FROM
PEAK HEATING IN THE AFTERNOON THROUGH OUR NOCTURNALLY FAVORED
OVERNIGHT HOURS EACH DAY. IT IS DIFFICULT TO DIAGNOSE SEVERE WEATHER
CHANCES WITH SO MANY OF THE DETAILS IN FLUX...BUT THERE WILL BE A
PERSISTENT THREAT OF HEAVY RAIN IN THIS SET UP WITH POSSIBLE
FLOODING CONCERNS INCREASING WITH EACH EVENT. THIS SITUATION WILL BE
CLOSELY MONITORED OVER THE NEXT SEVERAL DAYS. OTHERWISE...MADE
LITTLE CHANGE TO THE FORECAST KEEPING THE FAR PERIODS FROM FRIDAY
ONWARD DRY FOR NOW AND MODERATING TEMPERATURE FORECASTS TO ACCOUNT
FOR LIKELY CLOUD COVER AND HIGH SURFACE/LOW-LEVEL MOISTURE.

&&

.AVIATION...18/00Z
SOMEWHAT COMPLICATED FIRST 12 HOURS OF FCST. WARM FRONT DRAPED OVER
EASTERN SECTIONS OF FORECAST AREA WTIH APPROACHING SHORT WAVE AND
COLD FRONT FROM THE NORTHWEST TNT. EXTREME INSTABILITY IN PLACE ONCE
AGAIN THIS EVENING. STORMS ALREADY FIRING OVER EASTERN SD AND
CENTRAL NE AND EXPECTED TO FILL IN AS EVENING PROGRESSES. UNLIKE
LAST NIGHT...SHEAR...INSTABILITY...AND MOISTURE AXIS ALL LINE UP
INTO OUR FCST AREA FOR THE NIGHT HOURS. H700 TEMPS NEAR 12C OVER FAR
WEST IA...WITH SLIGHTLY COOLER TEMPS OVER THE CENTRAL AND EAST. HAVE
ADDED CONVECTIVE GUSTS TO 45KTS FOR NOW FOR KFOD AND KDSM WITH
EXPECTED ARRIVAL OF STORMS BETWEEN 05Z AND 09Z...SLIGHTLY LESSER
WINDS AT KALO AND KMCW. FORWARD PROPAGATION VECTORS SUGGEST 50-55KTS
MOVEMENT...SO CONCEIVABLY IF STRAIGHT LINE WIND SYSTEM DEVELOPS...
GUSTS OF 60 TO 80KTS MAY NOT BE OUT OF THE QUESTION. MESO MODELS ARE
TRENDING TOWARD DIMINISHING THE COVERAGE OF THE STORMS AFT 04Z...
WITH THE EXCEPTION OF THE 18Z NAM 12KM MODEL WHICH MAINTAINS MCS
STRENGTH OVERNIGHT. NEEDLESS TO SAY...POTENTIAL EXISTS FOR
SIGNIFICANT WIND EVENT LATER THIS EVENING...SO AREA AIRPORT MANAGERS
MAY WANT TO CONSIDER/EXERCISE ANY OPERATION PLANS FOR HIGH WIND
EVENTS. REMAINDER OF FORECAST QUIETS DOWN WITH WEAK HIGH BUILDING IN
FOR THE REMAINDER OF THE PERIOD. VFR CIGS AND LIGHT NW WINDS AFT 13Z
SUN EXPECTED FOR MOST OF THE DAY. /REV

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE

&&

SHORT TERM...COGIL
LONG TERM...LEE
AVIATION...REV

Hazardous weather outlook, Jul 17, 9:24 PM CST, 46 minutes before

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
1024 PM CDT SAT JUL 17 2010

IAZ033>035-044>048-057>062-070>075-081>086-092>097-181100-
SAC-CALHOUN-WEBSTER-CRAWFORD-CARROLL-GREENE-BOONE-STORY-AUDUBON-
GUTHRIE-DALLAS-POLK-JASPER-POWESHIEK-CASS-ADAIR-MADISON-WARREN-
MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-
RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS-
1024 PM CDT SAT JUL 17 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT

THUNDERSTORMS WILL ADVANCE SOUTH AND EAST INTO THE STATE TONIGHT.
SEVERE STORMS ARE EXPECTED WITH DAMAGING WINDS IN EXCESS OF 70
MPH THE MAIN THREAT. AN ISOLATED TORNADO IS ALSO POSSIBLE NORTH OF
INTERSTATE 80. LOCALLY HEAVY RAINS MAY ALSO OCCUR WITH THE POTENTIAL
FOR FLASH FLOODING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THUNDERSTORM CHANCES WILL LINGER OVER CENTRAL AND SOUTHERN IOWA
INTO SUNDAY AND SUNDAY NIGHT BEFORE PUSHING BACK NORTHWARD OVER
MUCH OF IOWA NEXT WEEK. THE POTENTIAL FOR LOCALLY HEAVY RAINS AND
POSSIBLY FLASH FLOODING WILL CONTINUE. THERE MAY ALSO BE A FEW
INSTANCES OF SEVERE WEATHER...BUT DETAILS REGARDING THE TIMING AND
MAGNITUDE OF THOSE EVENTS WILL BE BETTER DETERMINED IN THE COMING
DAYS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED TONIGHT.

IAZ004>007-015>017-023>028-181100-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-
1024 PM CDT SAT JUL 17 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT
THUNDERSTORMS WILL ADVANCE SOUTH AND EAST INTO THE STATE TONIGHT.
THERE IS A MODERATE RISK OF SEVERE WEATHER WITH DAMAGING WIND IN
EXCESS OF 70 MPH POSSIBLE AND LARGE HAIL. AN ISOLATED TORNADO IS
ALSO POSSIBLE. LOCALLY HEAVY RAINS MAY ALSO OCCUR WITH THE POTENTIAL
FOR FLASH FLOODING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THUNDERSTORM CHANCES WILL RETURN TO THE FORECAST LATE MONDAY
LASTING THROUGH THE NEXT WORK WEEK. THE POTENTIAL FOR LOCALLY
HEAVY RAINS AND POSSIBLY FLASH FLOODING WILL CONTINUE AS WELL. THERE
MAY ALSO BE A FEW INSTANCES OF SEVERE WEATHER...BUT DETAILS
REGARDING THE TIMING AND MAGNITUDE OF THOSE EVENTS WILL BE BETTER
DETERMINED IN THE COMING DAYS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED TONIGHT.

IAZ036>039-049-050-181100-
HAMILTON-HARDIN-GRUNDY-BLACK HAWK-MARSHALL-TAMA-
1024 PM CDT SAT JUL 17 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...TONIGHT

THUNDERSTORMS ARE EXPECTED NORTH AND WEST OF IOWA DURING THE
EVENING HOURS AND THEN ADVANCE SOUTH AND EAST INTO THE STATE
TONIGHT. SEVERE STORMS ARE EXPECTED WITH DAMAGING WIND IN EXCESS OF
70 MPH AND LARGE HAIL THE MAIN THREATS. AN ISOLATED TORNADO IS ALSO
POSSIBLE. LOCALLY HEAVY RAINS MAY ALSO OCCUR WITH THE POTENTIAL FOR
FLASH FLOODING.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THUNDERSTORM CHANCES WILL LINGER OVER CENTRAL AND SOUTHERN IOWA
INTO SUNDAY AND SUNDAY NIGHT BEFORE PUSHING BACK NORTHWARD OVER
MUCH OF IOWA NEXT WEEK. THE POTENTIAL FOR LOCALLY HEAVY RAINS AND
POSSIBLY FLASH FLOODING WILL CONTINUE. THERE MAY ALSO BE A FEW
INSTANCES OF SEVERE WEATHER...BUT DETAILS REGARDING THE TIMING AND
MAGNITUDE OF THOSE EVENTS WILL BE BETTER DETERMINED IN THE COMING
DAYS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL LIKELY BE NEEDED TONIGHT.

COGIL/REV

In the hours before

Special weather statement, Jul 17, 10:08 PM CST, 2 minutes before

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
1108 PM CDT SAT JUL 17 2010

IAZ023-024-034-035-180515-
POCAHONTAS-HUMBOLDT-CALHOUN-WEBSTER-
INCLUDING THE CITIES OF...POCAHONTAS...HUMBOLDT...ROCKWELL CITY...
FORT DODGE
1108 PM CDT SAT JUL 17 2010

...SEVERE THUNDERSTORMS LIKELY TONIGHT...

SEVERE THUNDERSTORMS JUST ENTERING EMMET AND PALO ALTO COUNTY WILL
CONTINUE MOVING SOUTHEAST AT 30 MPH POSSIBLY REACHING
POCAHONTAS...HUMBOLDT...CALHOUN AND WEBSTER COUNTIES BETWEEN
MIDNIGHT AND 100 AM. WINDS UP TO 80 MPH AND UP TO QUARTER SIZED
HAIL MAY OCCUR WITH THE PASSAGE OF THESE STORMS.

TORRENTIAL RAINS...FREQUENT LIGHTNING...AND FLASH FLOODING MAY BE
POSSIBLE AS WELL.

SMALL

The radar

The Sioux Falls radar (KFSD), 148 km away, was scanning. The volume nearest the first event began at 04:10 UTC.

Open the radar archive at this moment

Event by event

56 thunderstorm wind, 4 hail, 4 heavy rain, 3 flash flood, 1 lightning. Local standard time, as filed.

Hail, Emmet

When: July 17, 10:10 PM CST
Where: Emmet County, 3.01 mi W of Estherville
Measured: 1 in hail
Property damage: $1,000
Crop damage: $10,000
Reported by: Trained Spotter
Coordinates: 43.420, -94.910

Mostly dime to nickel size hail reported.

Hail, Palo Alto

When: July 17, 10:25 PM CST
Where: Palo Alto County, 4.09 mi W of Graettinger
Measured: 1.75 in hail
Property damage: $5,000
Crop damage: $15,000
Reported by: Trained Spotter
Coordinates: 43.240, -94.850

Hail, Palo Alto

When: July 17, 10:25 PM CST
Where: Palo Alto County, 3.78 mi WNW of Graettinger
Measured: 1.25 in hail
Property damage: $5,000
Crop damage: $200,000
Reported by: Public
Coordinates: 43.250, -94.840

Crop damage included bean plant heights being cut in half and leaves stripped from corn.

Thunderstorm Wind, Palo Alto

When: July 17, 10:40 PM CST
Where: Palo Alto County, 1.22 mi SE of Emmetsburg
Measured: 61 kt (70 mph) estimated gust
Property damage: $10,000
Crop damage: $10,000
Reported by: Trained Spotter
Coordinates: 43.110, -94.680

Numerous trees down, some uprooted.

Thunderstorm Wind, Kossuth

When: July 17, 11:10 PM CST
Where: Kossuth County, Whittemore
Measured: 52 kt (60 mph) estimated gust
Property damage: $5,000
Reported by: Newspaper
Coordinates: 43.070, -94.420

Strong winds downed several trees in the Whittemore area.

Thunderstorm Wind, Pocahontas

When: July 17, 11:20 PM CST
Where: Pocahontas County, 3.6 mi NNW of Havelock
Measured: 61 kt (70 mph) estimated gust
Property damage: $25,000
Crop damage: $50,000
Reported by: Trained Spotter
Coordinates: 42.880, -94.720

Barn doors were blown off. Also crop damage was reported.

Hail, Pocahontas

When: July 17, 11:38 PM CST
Where: Pocahontas County, 2.53 mi W of Plover
Measured: 1 in hail
Property damage: $1,000
Crop damage: $10,000
Reported by: Fire Department/Rescue
Coordinates: 42.880, -94.680

Hail report was relayed by KICD radio in Spencer.

Thunderstorm Wind, Humboldt

When: July 17, 11:40 PM CST
Where: Humboldt County, Dakota City
Measured: 65 kt (75 mph) estimated gust
Property damage: $200,000
Crop damage: $100,000
Reported by: Law Enforcement
Coordinates: 42.720, -94.220

Local law enforcement reports large limbs down across Humboldt County as well as large trees broken and uprooted near the county fairgrounds.

Thunderstorm Wind, Humboldt

When: July 18, 12:00 AM CST
Where: Humboldt County, Dakota City
Measured: 65 kt (75 mph) estimated gust
Property damage: $100,000
Reported by: Law Enforcement
Coordinates: 42.720, -94.220

Humboldt County sheriff reported 70 to 80 MPH winds in town.

Heavy Rain, Webster

When: July 18, 12:00 AM CST to 1:00 AM CST
Where: Webster County, 1.23 mi NW of Ft Dodge
Reported by: Mesonet
Coordinates: 42.510, -94.200

Rainfall of 1.7 inches in the hour between 0000 and 0100 CST.

Thunderstorm Wind, Humboldt

When: July 18, 12:05 AM CST
Where: Humboldt County, 0.86 mi NE of Dakota City
Measured: 61 kt (70 mph) estimated gust
Property damage: $25,000
Reported by: Trained Spotter
Coordinates: 42.730, -94.210

Trained spotter estimated wind of 70 MPH.

Thunderstorm Wind, Webster

When: July 18, 12:21 AM CST
Where: Webster County, 2.57 mi SW of Badger
Measured: 56 kt (64 mph) estimated gust
Property damage: $50,000
Crop damage: $10,000
Reported by: Trained Spotter
Coordinates: 42.590, -94.180

Estimated winds of 60 to 70 MPH with 2 to 4 inch diameter tree branches down. Visibility near zero in heavy rain.

Thunderstorm Wind, Wright

When: July 18, 12:28 AM CST
Where: Wright County, Eagle Grove
Measured: 50 kt (58 mph) measured gust
Property damage: $10,000
Reported by: Mesonet
Coordinates: 42.670, -93.900

Thunderstorm Wind, Webster

When: July 18, 12:45 AM CST
Where: Webster County, 0.69 mi S of Palm Grove
Measured: 65 kt (75 mph) estimated gust
Property damage: $50,000
Crop damage: $10,000
Reported by: Law Enforcement
Coordinates: 42.320, -94.180

Local law enforcement reports a grain bin blown over on 320th St near Palm Grove.

Thunderstorm Wind, Hamilton

When: July 18, 12:45 AM CST
Where: Hamilton County, 0.69 mi S of Webster City
Measured: 65 kt (75 mph) estimated gust
Property damage: $250,000
Crop damage: $100,000
Reported by: Law Enforcement
Coordinates: 42.460, -93.820

Local law enforcement reports trees and power lines down at several locations around Hamilton County with the bulk of the damage in the Webster City and Kamrar areas. Widespread power outages after the storm had only been partly restored by morning.

Thunderstorm Wind, Hamilton

When: July 18, 1:00 AM CST
Where: Hamilton County, 1.68 mi ESE of Webster City Arpt
Measured: 52 kt (60 mph) estimated gust
Property damage: $2,000
Reported by: Trained Spotter
Coordinates: 42.420, -93.840

Numerous small tree branches blown down.

Heavy Rain, Polk

When: July 18, 1:00 AM CST to 2:00 AM CST
Where: Polk County, 1.47 mi NNW of Polk City
Reported by: Mesonet
Coordinates: 41.790, -93.730

Rainfall of 2.36 inches fell in one hour between 0100 and 0200 CST.

Thunderstorm Wind, Webster

When: July 18, 1:00 AM CST
Where: Webster County, 0.4 mi WNW of Gowrie
Measured: 53 kt (61 mph) estimated gust
Property damage: $5,000
Reported by: CoCoRaHS
Coordinates: 42.282, -94.307

Large branches were blown down by the wind.

Heavy Rain, Story

When: July 18, 1:00 AM CST to 8:43 AM CST
Where: Story County, Slater
Reported by: Emergency Manager
Coordinates: 41.880, -93.680

Story County Emergency Manager reported 3.25 inches of rain from last nights storm.

Thunderstorm Wind, Boone

When: July 18, 1:05 AM CST
Where: Boone County, 2.81 mi S of Boxholm
Measured: 52 kt (60 mph) estimated gust
Property damage: $10,000
Reported by: Emergency Manager
Coordinates: 42.140, -94.110

Half inch size hail reported with 60 MPH winds in Boxholm.

Thunderstorm Wind, Boone

When: July 18, 1:12 AM CST
Where: Boone County, 1.38 mi S of Boone
Measured: 65 kt (75 mph) estimated gust
Property damage: $200,000
Crop damage: $50,000
Reported by: Law Enforcement
Coordinates: 42.050, -93.880

Local law enforcement reports trees and power lines down in Boone and across the county with some roads closed due to debris.

Flash Flood, Hamilton

When: July 18, 1:15 AM CST to 5:00 AM CST
Where: Hamilton County, 0.69 mi S of Webster City to 1.36 mi NE of Webster City
Cause: Heavy Rain
Property damage: $100,000
Reported by: Law Enforcement
Coordinates: 42.460, -93.820

Local law enforcement reports manhole covers blown off and streets flooded in Webster City. At least 2 cars that attempted to drive through the water were flooded and stalled.

Thunderstorm Wind, Boone

When: July 18, 1:23 AM CST
Where: Boone County, 1.38 mi S of Boone
Measured: 56 kt (64 mph) measured gust
Property damage: $25,000
Reported by: AWOS
Coordinates: 42.050, -93.880

Thunderstorm Wind, Boone

When: July 18, 1:23 AM CST
Where: Boone County, 1.38 mi S of Boone
Measured: 61 kt (70 mph) estimated gust
Property damage: $75,000
Reported by: NWS Employee
Coordinates: 42.050, -93.880

Numerous branches down across the city of Boone. Largest was at least 18 inches in diameter.

Thunderstorm Wind, Boone

When: July 18, 1:25 AM CST
Where: Boone County, 2.31 mi SSW of Boone Muni Arpt
Measured: 52 kt (60 mph) estimated gust
Property damage: $5,000
Reported by: NWS Employee
Coordinates: 42.020, -93.870

NWS employee estimated 60 MPH wind gust.

Thunderstorm Wind, Boone

When: July 18, 1:27 AM CST
Where: Boone County, 3.38 mi ENE of Madrid
Measured: 61 kt (70 mph) estimated gust
Property damage: $100,000
Crop damage: $50,000
Reported by: Law Enforcement
Coordinates: 41.900, -93.790

Local law enforcement reports power lines and trees down across the county. Some roads blocked by debris and a house struck by a tree on 320th about 2 miles northeast of Madrid.

Thunderstorm Wind, Boone

When: July 18, 1:28 AM CST
Where: Boone County, 1.54 mi E of Ericson
Measured: 63 kt (72 mph) measured gust
Property damage: $50,000
Reported by: Mesonet
Coordinates: 42.020, -93.770

Thunderstorm Wind, Story

When: July 18, 1:30 AM CST
Where: Story County, 1.5 mi E of Ames
Measured: 61 kt (70 mph) estimated gust
Property damage: $25,000
Reported by: CoCoRaHS
Coordinates: 42.030, -93.591

Tree damage reported and power pole snapped.

Thunderstorm Wind, Story

When: July 18, 1:30 AM CST
Where: Story County, 0.86 mi SW of Ames
Measured: 65 kt (75 mph) estimated gust
Property damage: $500,000
Crop damage: $100,000
Reported by: Emergency Manager
Coordinates: 42.020, -93.630

Story County Emergency Manager reports widespread significant tree damage in and around Ames. Some trees uprooted and others snapped off. Empty grain bins and outbuildings damaged across the county. A tree fell on a shed at Iowa State University.

Thunderstorm Wind, Story

When: July 18, 1:38 AM CST
Where: Story County, 0.86 mi SW of Ames
Measured: 62 kt (71 mph) measured gust
Property damage: $50,000
Reported by: ASOS
Coordinates: 42.020, -93.630

Thunderstorm Wind, Story

When: July 18, 1:40 AM CST
Where: Story County, 0.86 mi SW of Ames
Measured: 52 kt (60 mph) measured gust
Property damage: $25,000
Reported by: Trained Spotter
Coordinates: 42.020, -93.630

Thunderstorm Wind, Story

When: July 18, 1:40 AM CST
Where: Story County, 1.54 mi W of Nevada Muni Arpt
Measured: 61 kt (70 mph) estimated gust
Property damage: $50,000
Crop damage: $100,000
Reported by: Emergency Manager
Coordinates: 42.020, -93.510

Story County Emergency Manager reports trees destroyed including a 100 year old oak, corn shredded, and power lines down 3 miles west of Nevada.

Thunderstorm Wind, Boone

When: July 18, 1:40 AM CST
Where: Boone County, 1.54 mi E of Madrid
Measured: 51 kt (59 mph) measured gust
Property damage: $5,000
Reported by: Trained Spotter
Coordinates: 41.880, -93.820

Several large trees greater than 12 inches in diameter felled. Large tree branches of 6 inches or greater also broken.

Thunderstorm Wind, Story

When: July 18, 1:43 AM CST
Where: Story County, 2.57 mi E of Ames
Measured: 58 kt (67 mph) measured gust
Property damage: $25,000
Reported by: Mesonet
Coordinates: 42.030, -93.570

Thunderstorm Wind, Polk

When: July 18, 1:46 AM CST
Where: Polk County, 0.86 mi SE of Ankeny
Measured: 56 kt (64 mph) estimated gust
Property damage: $100,000
Reported by: Amateur Radio
Coordinates: 41.720, -93.610

Estimated 60 to 70 MPH winds on the north side of Ankeny.

Thunderstorm Wind, Polk

When: July 18, 1:50 AM CST
Where: Polk County, 2.14 mi NNE of Dodge Fld Arpt
Measured: 61 kt (70 mph) estimated gust
Property damage: $10,000
Reported by: NWS Employee
Coordinates: 41.710, -93.710

Beaver Drive closed by Camp Dodge as crews remove fallen tree across road.

Thunderstorm Wind, Polk

When: July 18, 1:55 AM CST
Where: Polk County, 0.69 mi N of Windsor Hgts
Measured: 65 kt (75 mph) estimated gust
Property damage: $75,000
Reported by: Public
Coordinates: 41.610, -93.720

Citizen reports numerous large trees down on 74th St in Windsor Heights. A 3 to 4 foot diameter White Pine was snapped at the base and another tree fell onto a garage and through a roof.

Thunderstorm Wind, Polk

When: July 18, 1:57 AM CST
Where: Polk County, 0.52 mi E of Herrold
Measured: 57 kt (66 mph) measured gust
Property damage: $3,000
Reported by: Official NWS Observations
Coordinates: 41.720, -93.740

NWS office in Johnston.

Thunderstorm Wind, Polk

When: July 18, 2:00 AM CST
Where: Polk County, 0.86 mi SE of Lovington
Measured: 73 kt (84 mph) measured gust
Property damage: $200,000
Reported by: Trained Spotter
Coordinates: 41.640, -93.690

Measured gust with several trees down.

Thunderstorm Wind, Polk

When: July 18, 2:00 AM CST
Where: Polk County, 0.86 mi SW of Lovington
Measured: 65 kt (75 mph) estimated gust
Property damage: $150,000
Reported by: NWS Employee
Coordinates: 41.640, -93.710

Telephone pole snapped near the top. Power in the area reportedly out.

Thunderstorm Wind, Story

When: July 18, 2:00 AM CST
Where: Story County, 0.2 mi W of Gilbert
Measured: 57 kt (66 mph) estimated gust
Property damage: $10,000
Reported by: CoCoRaHS
Coordinates: 42.120, -93.654

Tree damage reported and yard tables moved.

Thunderstorm Wind, Polk

When: July 18, 2:01 AM CST
Where: Polk County, 3.8 mi N of Grimes
Measured: 69 kt (79 mph) estimated gust
Property damage: $50,000
Reported by: CoCoRaHS
Coordinates: 41.735, -93.800

Widespread tree damage in the area caused by 75 to 85 MPH winds.

Thunderstorm Wind, Dallas

When: July 18, 2:04 AM CST
Where: Dallas County, 0.86 mi SE of Shuler Mine
Measured: 56 kt (64 mph) estimated gust
Property damage: $15,000
Reported by: Trained Spotter
Coordinates: 41.620, -93.870

Trained spotter estimated winds near 65 MPH.

Thunderstorm Wind, Polk

When: July 18, 2:05 AM CST
Where: Polk County, 1.24 mi NE of Ankeny
Measured: 61 kt (70 mph) estimated gust
Property damage: $10,000
Reported by: Trained Spotter
Coordinates: 41.740, -93.600

Numerous 4 to 6 inch diameter tree limbs down by the high winds.

Thunderstorm Wind, Polk

When: July 18, 2:05 AM CST
Where: Polk County, 0.86 mi SE of Ankeny
Measured: 65 kt (75 mph) estimated gust
Property damage: $50,000
Reported by: Law Enforcement
Coordinates: 41.720, -93.610

Canopy at Caseys blown down.

Thunderstorm Wind, Dallas

When: July 18, 2:08 AM CST
Where: Dallas County, 3.17 mi SSE of Hadden Hill
Measured: 61 kt (70 mph) estimated gust
Property damage: $10,000
Reported by: NWS Employee
Coordinates: 41.580, -93.800

Also with pea size hail falling.

Thunderstorm Wind, Dallas

When: July 18, 2:08 AM CST
Where: Dallas County, 0.86 mi SW of Adel
Measured: 65 kt (75 mph) estimated gust
Property damage: $50,000
Reported by: Law Enforcement
Coordinates: 41.610, -94.030

Large tree limbs blown onto nearby roads. Some trees were uprooted.

Thunderstorm Wind, Polk

When: July 18, 2:09 AM CST
Where: Polk County, 1.24 mi NW of Urbandale
Measured: 61 kt (70 mph) estimated gust
Property damage: $25,000
Reported by: Trained Spotter
Coordinates: 41.640, -93.740

Trained spotter estimated wind gust to 70 MPH.

Thunderstorm Wind, Story

When: July 18, 2:10 AM CST
Where: Story County, Nevada
Measured: 61 kt (70 mph) estimated gust
Property damage: $10,000
Reported by: Trained Spotter
Coordinates: 42.020, -93.450

Numerous large trees and limbs down in town.

Thunderstorm Wind, Polk

When: July 18, 2:14 AM CST
Where: Polk County, 0.52 mi E of (Dsm)des Moines Intl
Measured: 52 kt (60 mph) measured gust
Property damage: $2,000
Reported by: ASOS
Coordinates: 41.530, -93.660

Thunderstorm Wind, Warren

When: July 18, 2:15 AM CST
Where: Warren County, 0.86 mi SW of Clarkson
Measured: 61 kt (70 mph) estimated gust
Property damage: $25,000
Crop damage: $15,000
Reported by: Trained Spotter
Coordinates: 41.490, -93.490

Former NWS employee reports numerous trees, some as large as 4 feet around, snapped off near John Goodhue Road in Carlisle.

Thunderstorm Wind, Polk

When: July 18, 2:20 AM CST
Where: Polk County, 0.52 mi E of (Dsm)des Moines Intl
Measured: 53 kt (61 mph) measured gust
Property damage: $2,000
Reported by: ASOS
Coordinates: 41.530, -93.660

Thunderstorm Wind, Madison

When: July 18, 2:21 AM CST
Where: Madison County, 0.69 mi N of Winterset
Measured: 69 kt (79 mph) estimated gust
Property damage: $25,000
Crop damage: $10,000
Reported by: Law Enforcement
Coordinates: 41.340, -94.020

A roof was blown off of a camper. Tree limbs 12 to 24 inches in diameter were broken. Power lines were also downed.

Thunderstorm Wind, Polk

When: July 18, 2:25 AM CST
Where: Polk County, 4.97 mi NE of Bondurant
Measured: 52 kt (60 mph) estimated gust
Property damage: $2,000
Reported by: Trained Spotter
Coordinates: 41.740, -93.390

Small tree branches blown down.

Thunderstorm Wind, Dallas

When: July 18, 2:26 AM CST
Where: Dallas County, 1.7 mi WSW of Hadden Hill
Measured: 57 kt (66 mph) estimated gust
Property damage: $100,000
Reported by: Law Enforcement
Coordinates: 41.610, -93.860

Large trees down in Waukee and Woodward. Power out across half of Waukee.

Thunderstorm Wind, Warren

When: July 18, 2:26 AM CST
Where: Warren County, 0.69 mi S of Indianola
Measured: 61 kt (70 mph) estimated gust
Property damage: $15,000
Reported by: Law Enforcement
Coordinates: 41.360, -93.570

Trees reported down on east Euclid Ave.

Thunderstorm Wind, Madison

When: July 18, 2:28 AM CST
Where: Madison County, 0.69 mi N of Winterset
Measured: 61 kt (70 mph) measured gust
Property damage: $5,000
Reported by: Mesonet
Coordinates: 41.340, -94.020

Thunderstorm Wind, Madison

When: July 18, 2:30 AM CST
Where: Madison County, 0.69 mi N of Winterset
Measured: 61 kt (70 mph) estimated gust
Property damage: $15,000
Reported by: Law Enforcement
Coordinates: 41.340, -94.020

Trees down with multiple power outages and downed transformers.

Thunderstorm Wind, Marion

When: July 18, 2:40 AM CST
Where: Marion County, 0.69 mi N of Pleasantville
Measured: 61 kt (70 mph) estimated gust
Property damage: $10,000
Reported by: Law Enforcement
Coordinates: 41.390, -93.270

Power lines reported down from strong winds.

Lightning, Black Hawk

When: July 18, 2:50 AM CST
Where: Black Hawk County, Raymond
Property damage: $10,000
Reported by: Newspaper
Coordinates: 42.470, -92.220

Thunderstorm Wind, Lucas

When: July 18, 3:07 AM CST
Where: Lucas County, 0.52 mi E of Chariton
Measured: 61 kt (70 mph) estimated gust
Property damage: $10,000
Reported by: Law Enforcement
Coordinates: 41.020, -93.310

A tree 12 inches in diameter was blown over by strong winds.

Heavy Rain, Marion

When: July 18, 3:43 AM CST
Where: Marion County, Knoxville
Reported by: Emergency Manager
Coordinates: 41.320, -93.100

Some areas of Knoxville reported street flooding.

Thunderstorm Wind, Appanoose

When: July 18, 3:48 AM CST
Where: Appanoose County, 1.25 mi ENE of Moravia
Measured: 65 kt (75 mph) estimated gust
Property damage: $50,000
Reported by: Law Enforcement
Coordinates: 40.890, -92.860

A barn was destroyed by high winds.

Thunderstorm Wind, Appanoose

When: July 18, 3:54 AM CST
Where: Appanoose County, 1.05 mi W of Rathbun
Measured: 52 kt (60 mph) estimated gust
Property damage: $5,000
Reported by: Trained Spotter
Coordinates: 40.800, -92.890

Very heavy rain and tree damage reported.

Thunderstorm Wind, Appanoose

When: July 18, 3:55 AM CST
Where: Appanoose County, 0.52 mi W of Mystic
Measured: 61 kt (70 mph) estimated gust
Property damage: $10,000
Reported by: Amateur Radio
Coordinates: 40.780, -92.940

Winds reported near 70 MPH and pea size hail.

Thunderstorm Wind, Appanoose

When: July 18, 4:00 AM CST
Where: Appanoose County, 1.48 mi NNW of Clarkdale
Measured: 63 kt (72 mph) measured gust
Property damage: $25,000
Reported by: Trained Spotter
Coordinates: 40.800, -92.910

Wind gust reported by a Ham Radio operator.

Flash Flood, Marion

When: July 18, 4:50 AM CST to 8:30 AM CST
Where: Marion County, Columbia to 0.58 mi N of Columbia
Cause: Heavy Rain
Property damage: $15,000
Reported by: Emergency Manager
Coordinates: 41.180, -93.150

Water was reported over 103rd Ave into Columbia near Highway 14.

Flash Flood, Marion

When: July 18, 4:50 AM CST to 8:30 AM CST
Where: Marion County, Knoxville to 0.82 mi E of Knoxville
Cause: Heavy Rain
Property damage: $25,000
Reported by: Emergency Manager
Coordinates: 41.320, -93.100

Four feet of water in some city streets. Cars were stalled.

What these are

Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
Thunderstorm Wind: Winds from a thunderstorm of 50 knots (58 mph) or more, or lower winds that caused damage or casualties. Measured gusts are marked MG, estimated EG.
Heavy Rain: Rainfall totals unusual for the place and season that did not produce a flood.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.
Lightning: A lightning strike that killed, injured or caused damage.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Iowa in 2010 Every state in 2010 This day in weather history Warnings in Iowa, July 2010

Sources

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: 233374, 233503, 233504, 233522, 248633, 233512, 233376, 233513, 233381, 233398, 233382, 233383, 233384, 233514, 233515, 233386, 233399, 233441, 233501, 233387, 233516, 233502, 233402, 233505, 233417, 233517, 233403, 233439, 233518, 233404, 233405, 233519, 233523, 233434, 233407, 233423, 233520, 233408, 233409, 233437, and more.