Tornado and Hail in Iowa, August 17, 2001

Name: Tornado and Hail in Iowa, August 17, 2001
Start: 2001-08-17T18:40
End: 2001-08-17T21:40
Location: Iowa

August 17, 2001 · NWS DMX · 9 events in 3 counties and zones

Moisture streamed northeast into Iowa ahead of a cold front approaching from the north. Dew point temperatures rose to +15 degrees C.

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: $245,000
Crop damage: $73,000
Events: 9

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.

Moisture streamed northeast into Iowa ahead of a cold front approaching from the north. Dew point temperatures rose to +15 degrees C. at 850 mb by early evening. At the same time, colder air was moving aloft. This destabilized the atmosphere with thunderstorms erupting in northwest Iowa by late afternoon. The small cluster of storms became severe and moved southeast into the DSM County Warning Area. For the most part, the storms produced hail due to the low freezing level. The freezing level was down to just over 12,000 feet at the time of the evening sounding at 0000 UTC. Numerous reports of one to two inch diameter hail were received from Crawford County southeast into Adams County. A tornado touched down in Crawford County near Buck Grove. The tornado tracked southeast a little over 6 miles, lifting just before crossing the Shelby County line southwest of Manilla. The tornado downed power lines, destroyed several out buildings, and caused extensive crop damage along its path.

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 Aug 17, 2:17 PM CST, 4 hours 23 minutes earlier.

Area forecast discussion, Aug 17, 2:17 PM CST, 4 hours 23 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
317 PM CDT FRI AUG 17 2001

...MAIN CHALLENGES THOUGH PERIOD TO BE PRECIP IN 1ST TWO PERIODS AND
LATER IN EXTENDED...

VAPOR LOOP INDICATING VARIOUS SHORT WAVES OF INTEREST...SOME WEAK
OVER NEB/SD AND THE OTHER STRONGER OVER SRN MANITOBA TO NRN MN AND
ERN ND.  AT THE SFC/80H...WARM FRONT OVR KS THIS AFTERNOON...AND
WEAK RIDGING ASSOC WITH DYING CONVECTION OVR MO.  AT 80H THIS
MORNING...10-13 DEWPOINTS POOLED OVR KS INTO SGF AREA...AND WOULD
EXPECT THESE TO PUSH FARTHER NORTH TONIGHT ON LLJ.

SHORT TERM...
QUESTION TNGT WL BE WHEN TO DVLP PCPN.  SVRL SFC TROFS NOTED
UPSTREAM AND TOUGH TO PICK OUT TRUE CDFNT.  MSTR AND CNVGNC
RELATIVELY WEAK AND LAPS ANLYS SHOWING ENOUGH CIN TO HOLD BACK SFC
DVLPMT...AT LEAST IN OUR FA.  NE CONVECTION SHOULD RMN JUST SW.
THUS WL LEAVE EVE DRY AS PCPN WL LIKELY WAIT TIL STG SHRT WV OVR
CANADA/MN BORDER DROPS SWD.  DIFFERENTAL PVA SHOULD MODIFY
ENVIRONMENT ENOUGH TO KEEP TSTMS ACRS MN GOING OVNGT DROPPING SWD
INTO IA WITH DYNAMICS AND DECENT WRM ADVCTN AHD OF SHRT WV.  DID NOT
WANT TO JUMP INTO LIKELY CATEGORY AS PCPN MAY DMSH SOMEWHAT WITH
LOSS OF HEATING...BUT DID RAISE CHCS.  SAW NO REASON TO DEVIATE FM
TEMP GUIDANCE.

LONG TERM...LITTLE REASON TO ARGUE WITH ETA/AVN TIMING HERE.  SOME
DIFFERENCES EARLY...BUT BY SAT...ETA CATCHES UP WITH AVN.  FWC/MAV
TEMPS NOT MUCH DIFFERENT THAN GOING ZFP EITHER.  EXPECT LINGERING
CONVECTION ALONG AND JUST BEHIND FRONT OVER CWA IN MORNING HOURS.
LIKELY NOT TO SEE MUCH THO IN WEST OF LINE FROM DNS TO MCW...THO
WILL CARRY A SMALL MORNING MENTION OF CONVECTION IN NW.
ELSEWHERE...CONVECTION SHOULD BE OVER BY 18Z OR SO WITH
DOWNGLIDE...DIV OF Q...AND SO FORTH. WITH COLD POOL ALOFT AND CAA AT
80H...WILL NOT GET RID OF CLOUDS TOO FAST THOUGH.

SAT NIGHT INTO MONDAY...LOOKS QUIET. EXPECT SOME CONVECTION OVER
PLAINS SUN NIGHT MAYBE IN WAA AND LLJ...BUT SHOULD STAY WEST OF CWA.

IN THE EXTENDED...TROFFINESS IN EAST FILLS WITH SOME PUSH TO THE
EAST OF THE WRN RIDGE.  EXPECT POTENTIAL FOR SOME SCT CONVECTION IN
VCNTY OF WRM FRONT AND TROF ON TUES.  FOR WED...LOOKS LIKE BEST
POTENTIAL FOR LL CONV HAS PUSHED NORTH...THOUGH THIS ISNT SET IN
STONE.  WILL GO DRY FOR WED NOW.  THU/FRI...AGAIN LOOKS LIKE
NIGHTTIME MCS POTENTIAL WITH RIDGE AXIS TO OUR EAST AND SOME
TROPICAL MOISTURE INFLUENCE.  SEASONABLE TEMPS.

.DSM...NONE

SMALL/SEARCY

In the hours before

Special weather statement, Aug 17, 4:45 PM CST, 1 hour 55 minutes before

CENTRAL IOWA THUNDERSTORM OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
545 PM CDT FRI AUG 17 2001

SYNOPSIS
A COLD FRONT EXTENDING FROM MINNESOTA INTO SOUTH DAKOTA AND EASTERN
NEBRASKA WILL MOVE INTO NORTHWEST IOWA LATER THIS EVENING...AND PASS
SOUTHEAST OF THE STATE ON SATURDAY.  THE AIRMASS IS MARGINALLY
UNSTABLE THIS EVENING AS LOW LEVEL MOISTURE INCREASES AND
TEMPERATURES FALL ALOFT.  ALTHOUGH THERE WILL BE SOME THREAT FOR
WIND AND TORNADOES...THE
PREDOMINANT SEVERE WEATHER THREAT WILL BE FOR HAIL.

SEE SITE SPECIFIC DETAILS BELOW FOR MORE INFORMATION.

IAZ004>007-015>017-023>025-033>035-044-181100-
CALHOUN-CERRO GORDO-CRAWFORD-EMMET-HANCOCK-HUMBOLDT-KOSSUTH-PALO
ALTO-POCAHONTAS-SAC-WEBSTER-WINNEBAGO-WORTH-WRIGHT-
INCLUDING THE CITIES OF...ALGONA...DENISON...ESTHERVILLE...FORT DODGE
AND MASON CITY
536 AM CDT FRI AUG 17 2001

* EVENT TIMING... FROM 630 PM THROUGH 1100 PM

* THREAT CATEGORIES...
     TORNADO.......... LOW
     DAMAGING WINDS... LOW
     LARGE HAIL....... LOW
     FLASH FLOODING... NOT EXPECTED

* SPOTTER ACTIVATION OUTLOOK... LOW

IAZ026>028-036>039-045>050-057>061-070>072-181100-
ADAIR-AUDUBON-BLACK
HAWK-BOONE-BREMER-BUTLER-CARROLL-CASS-DALLAS-FRANKLIN-GREENE-GRUNDY-
GUTHRIE-HAMILTON-HARDIN-JASPER-MADISON-MARSHALL-POLK-STORY-TAMA-
INCLUDING THE CITIES OF...AMES...ATLANTIC...BOONE...CARROLL...DES
MOINES...IOWA FALLS...MARSHALLTOWN...NEWTON...PERRY...WATERLOO...
WAVERLY AND WEBSTER CITY
536 AM CDT FRI AUG 17 2001

* EVENT TIMING... FROM 1000 PM UNTIL 400 AM

* THREAT CATEGORIES...
     TORNADO.......... NOT EXPECTED
     DAMAGING WINDS... LOW
     LARGE HAIL....... LOW
     FLASH FLOODING... NOT EXPECTED

* SPOTTER ACTIVATION OUTLOOK... LOW

IAZ062-073>075-081>086-092>097-181100-
ADAMS-APPANOOSE-CLARKE-DAVIS-DECATUR-LUCAS-MAHASKA-MARION-MONROE-
POWESHIEK-RINGGOLD-TAYLOR-UNION-WAPELLO-WARREN-WAYNE-
INCLUDING THE CITIES OF...CENTERVILLE...CHARITON...CRESTON...
GRINNELL...INDIANOLA...KNOXVILLE...LAMONI...OSKALOOSA...OTTUMWA AND
PELLA
536 AM CDT FRI AUG 17 2001

* EVENT TIMING... FROM 100 AM UNTIL 600 AM

* THREAT CATEGORIES...
     TORNADO.......... NOT EXPECTED
     DAMAGING WINDS... NOT EXPECTED
     LARGE HAIL....... LOW
     FLASH FLOODING... NOT EXPECTED

* SPOTTER ACTIVATION OUTLOOK... NOT EXPECTED

-------------------------------------------------------------------

THREAT KEY:
    TORNADO.......... ANY TORNADO OCCURRENCE
    DAMAGING WINDS... WINDS >= 58 MPH
    LARGE HAIL....... HAIL >= 3/4 INCH DIAMETER
    FLASH FLOODING... FLOODING CAUSED BY HEAVY RAINS WITHIN 6 HOURS
                      OF RAIN EVENT. POSES THREAT TO LIFE OR
                      PROPERTY.

THREAT CATEGORY KEY:  PROBABILITY OF THREAT OCCURRING WITHIN 25
                      MILES OF POINT WITHIN FORECAST AREA
    NONE....... NOT EXPECTED.  LESS THAN 5% ( 2% FOR TORNADOES)
    LOW........ 5-15% (2-15% FOR TORNADOES)
    MODERATE... 25-35%
    HIGH....... 45% OR GREATER

SPOTTER ACTIVATION OUTLOOK KEY:
    NOT EXPECTED
    LOW........ ACTIVATION POSSIBLE BUT NOT LIKELY
    MODERATE... POSSIBILITIES ABOUT 50-50
    HIGH....... ACTIVATION LIKELY

FOR MORE INFORMATION ON PROBABILISTIC SEVERE WEATHER OUTLOOKS...GO
TO THE STORM PREDICTION CENTER WEBSITE AT
WWW.SPC.NOAA.GOV/PRODUCTS/OUTLOOK/PROBINFO.HTML .

KNOLLHOFF

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

8 hail, 1 tornado. Local standard time, as filed.

Hail, Crawford

When: August 17, 6:40 PM CST
Where: Crawford County, 2 mi W of Denison
Measured: 1 in hail
Property damage: $3,000
Crop damage: $5,000
Reported by: EMERGENCY MANAGER
Coordinates: 41.500, -95.067

Hail, Crawford

When: August 17, 6:50 PM CST
Where: Crawford County, Denison Muni Arpt
Measured: 1 in hail
Property damage: $5,000
Crop damage: $5,000
Reported by: EMERGENCY MANAGER
Coordinates: 41.433, -95.050

Hail, Crawford

When: August 17, 6:50 PM CST
Where: Crawford County, Denison
Measured: 0.88 in hail
Property damage: $3,000
Crop damage: $3,000
Reported by: EMERGENCY MANAGER
Coordinates: 41.267, -94.883

Tornado, Crawford

When: August 17, 7:18 PM CST to 7:31 PM CST
Where: Crawford County, Buck Grove
Rating: F1
Path length: 6.3 mi
Path width: 50 yd
Property damage: $200,000
Crop damage: $20,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.133, -94.917

Several outbuilding destroyed and many crops flattened.

Hail, Cass

When: August 17, 8:24 PM CST
Where: Cass County, 7 mi NNW of Atlantic
Measured: 1.75 in hail
Property damage: $7,000
Crop damage: $10,000
Reported by: EMERGENCY MANAGER
Coordinates: 40.983, -94.733

Hail, Cass

When: August 17, 8:28 PM CST
Where: Cass County, 3 mi NW of Atlantic
Measured: 1.75 in hail
Property damage: $7,000
Crop damage: $10,000
Reported by: EMERGENCY MANAGER
Coordinates: 42.017, -95.383

Hail, Cass

When: August 17, 8:50 PM CST
Where: Cass County, Cumberland
Measured: 1.75 in hail
Property damage: $10,000
Crop damage: $10,000
Reported by: TRAINED SPOTTER
Coordinates: 41.983, -95.383

Hail, Adams

When: August 17, 9:05 PM CST
Where: Adams County, 14 mi NW of Corning
Measured: 1 in hail
Property damage: $3,000
Crop damage: $5,000
Reported by: TRAINED SPOTTER
Coordinates: 42.017, -95.350

Hail, Adams

When: August 17, 9:40 PM CST
Where: Adams County, Corning
Measured: 1 in hail
Property damage: $7,000
Crop damage: $5,000
Reported by: LAW ENFORCEMENT
Coordinates: 41.917, -95.400

What these are

Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
Tornado: A violently rotating column of air in contact with the ground and extending from a thunderstorm, filed with its path, width and Fujita or Enhanced Fujita rating from the damage survey.

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

The same day elsewhere

Every storm in Iowa in 2001 Every state in 2001 This day in weather history The tornado archive for Iowa, 2001 Warnings in Iowa, August 2001

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: 5260903, 5260904, 5260963, 5260964, 5260965, 5260966, 5260967, 5260968, 5260969.