Hail and Damaging Winds in Iowa, July 29, 2008

Name: Hail and Damaging Winds in Iowa, July 29, 2008
Start: 2008-07-29T14:30
End: 2008-07-29T14:44
Location: Iowa

July 29, 2008 · NWS DMX · 4 events in 1 county or zone

A somewhat complex weather situation developed synoptically as two weather systems approached the area. The first was the approach of a weak cold front from the northwest.

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: $5,000
Crop damage: $10,000
Events: 4

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 somewhat complex weather situation developed synoptically as two weather systems approached the area. The first was the approach of a weak cold front from the northwest. The front stretched northeast to southwest across far northwest Iowa by mid afternoon. The second was the approach of the remnants of a former hurricane, Dolly. The upper low associated with Dolly was over northeast Kansas by the mid afternoon hours and was moving east-northeast. To the south and into the southwest part of the CWA, a large rain shield was in place associated with the remnants. Meanwhile, a line of thunderstorms developed ahead of the cold front over northwest Iowa. In between the two, the airmass became quite unstable with CAPE rising to around 4000 J/kg and the lifted index falling to around -10 C. Shear was quite weak, only around 20 kts, making it difficult to maintain significant rotation. Downdraft CAPE was round 700 J/kg and CAPE in the -10 to -30 C. layer of the atmosphere was in the 600 to 800 J/kg range. The freezing level was quite high due to the tropical nature of the atmosphere and was between 14,000 and 15,000 feet. Plenty of moisture was available with precipitable water in the 1.75 to 2 inch range. Thunderstorms fired in the area between the two systems around mid afternoon. The storms became severe for a brief period of time and produced nickel to quarter size hail and winds to 60 MPH in the Ames area. The initial event only lasted one storm cycle before the storms collapsed.

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 29, 2:05 PM CST, 25 minutes earlier.

Area forecast discussion, Jul 29, 2:05 PM CST, 25 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
305 PM CDT TUE JUL 29 2008

.SHORT TERM...TONIGHT

18Z SFC ANALYSIS SHOWS A WEAKENING COLD FRONT INTO NORTHWEST IA WITH
A TROUGH AHEAD OF IT FROM NORTHEAST IOWA TO JUST NW OF DSM. A HIGH
PRESSURE BUBBLE HAS DEVELOPED BETWEEN THE COLD FRONT AND THE LOW
PRESSURE OVER SOUTH CENTRAL KANSAS AND EXTENDS INTO SOUTHWEST IOWA.
THIS HIGH PRESSURE IS LIKELY BEING REINFORCED BY RAIN-COOLED AIR
ASSOCIATED WITH DEFORMATION AXIS RAINFALL APPROACHING SRN IA.
INSTABILITY IN QUESTION THIS AFTERNOON. THE RUC AND SPC ANALYSIS
GRAPHICS SHOW MUCH OF THE AREA NOW MODERATELY UNSTABLE WITH LITTLE
CAPPING...IF ANY. HOWEVER...LAPS AND RUC SOUNDINGS SHOW A LOWER WARM
NOSE. GIVEN DEGREE OF CLOUD COVER OVER SOUTHERN IA...FEEL THAT BEST
CHANCES FOR LATE AFTN AND EVENING THUNDERSTORMS WILL BE BETWEEN
INTERSTATE 80 AND THE COLD FRONT DROPPING SOUTHEAST...AND ALSO
PERHAPS IN THE FAR SOUTHEAST NEAR OTTUMWA. OTHERWISE...FAR SOUTHERN
IOWA SHOULD EXPERIENCE A FEW HOURS OF LIGHT TO MODERATE RAIN WITH
EMBEDDED THUNDER POSSIBLE.

.LONG TERM...WEDNESDAY THROUGH MONDAY

HIGH PRESSURE WILL WEAKLY BUILD INTO THE UPPER MIDWEST ON WEDNESDAY
BUT REMNANTS OF DOLLY WILL STILL BE EVIDENCED IN NORTHERN/NORTHEAST
MO.  ADDITIONAL CONVECTION SHOULD DEVELOP IN VICINITY OF THE WASHED
OUT FRONT FROM TODAY AND THE MOISTURE FROM DOLLY.  THIS MAY CLIP THE
FAR SOUTH OR SOUTHEAST BUT WE ARE NOT EXPECTING ANY MAJOR PRECIP OUT
OF THAT.  LATER ON WEDNESDAY/WEDNESDAY NIGHT...THE HIGH SHIFTS EAST
AS A LOW PRESSURE SYSTEM DEVELOPS IN THE HIGH PLAINS IN RESPONSE TO
A WEAK SHORTWAVE AND WARM ADVECTION.  THE SURFACE LOW WILL SET UP A
BOUNDARY OVER NORTHERN IOWA/SOUTHERN MINNESOTA OR SOUTH DAKOTA.
THERE IS VIRTUALLY NO SHEAR BUT CAPES BETWEEN 1200 AND 2600 J/KG
THROUGH THE WEDNESDAY NIGHT PERIOD.  I FELT THIS WARRANTED AT LEAST
A MENTION OF SLIGHT CHC OR CHANCE WHICH WAS EXPENDED DURING THE
OVERNIGHT PORTION OF THE PERIOD.

FOR THURSDAY...WARM ADVECTION REALLY STRENGTHENS AS A THERMAL RIDGE
PUSHES IN.  THE AFOREMENTIONED SURFACE LOW DRIFTS INTO MN LEAVING IA
STRONGLY IN THE WARM SECTOR.  MODELS STILL INDICATE A WEAK VORT MAX
AND SHORT WAVE PUSHING MAINLY ACROSS THE HIGH PLAINS BUT THE UPPER
LEVEL FLOW DOES BECOME MORE NW OVER NORTHERN AND EASTERN IOWA SO
SHOULD AN MCS DEVELOP IN THIS VICINITY IT MAY CLIP FAR NORTHERN IOWA
LATER THURSDAY NIGHT.  THIS HAS BEEN ACCOUNTED FOR ALREADY AND WE
WILL KEEP SLIGHT CHANCES IN FOR NOW.  MODEL TRENDS HAVE BEEN FURTHER
NORTH WITH THIS FEATURE WITH EACH RUN SO THIS MAY BE ADJUSTED/
REMOVED IN LATER PERIODS.

FOR THE WEEKEND THE UPPER LEVEL RIDGE BUILD OVER THE UPPER MIDWEST
AND WE TURN HOT.  TEMPS WILL BE TEMPERED SOME BY CLOUD COVER AND THE
AMOUNT OF MOISTURE IN THE AIR BUT MID 90S NOW SEEM LIKELY AND MAYBE
EVEN HIGHER READINGS.  A LARGE LOW PRESSURE SYSTEM IS SLATED TO
FLATTEN THE RIDGE LATE IN THE EXTENDED...BEGINNING SUNDAY NIGHT
THROUGH MONDAY NIGHT.  BOTH THE GFS AND EURO POINTING TO A MORE
ACTIVE PERIOD OVER NORTHERN IOWA AS SEVERAL SHORT WAVES MOVE EAST
THROUGH THE PERIOD.  BACKED TEMPS DOWN AS WELL FOR SUNDAY AND MONDAY
DUE TO CLOUD COVER AND THE POTENTIAL FOR STORMS.

&&

.AVIATION...29/18Z
WILL SEE ISOLATED TO SCATTERED CONVECTION OVER CENTRAL IA THROUGH
02Z WITH LEAST COVERAGE AND EARLIER ENDING AT NRN SITES.
UNCERTAINTIES WITH TIMING AND LOCATION PRECLUDE ANYTHING MORE THAN
VC OR CB IN TAFS AT THIS TIME. HAVE TO HANG ON TO MVFR CEILINGS AT
KOTM FOR A LITTLE WHILE LONGER. AFTER CONVECTION MOVES OUT
TONIGHT...DECENT CHANCES OF HAVING MVFR VSBYS DEVELOP...ESPECIALLY
WHERE IT CLEARS BEST.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

SHORT TERM/AVIATION...MOYER
LONG TERM...FAB

Hazardous weather outlook, Jul 29, 10:40 AM CST, 3 hours 50 minutes before

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1140 AM CDT TUE JUL 29 2008

IAZ004>007-015>017-023>028-033>039-301645-
EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-
POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN-
WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-
1140 AM CDT TUE JUL 29 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

ISOLATED SCATTERED THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON. AN ISOLATED
SEVERE STORM OR TWO IS POSSIBLE WITH NICKEL SIZED HAIL AND 60 MPH
THE PRIMARY THREATS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

SCATTERED THUNDERSTORMS ARE POSSIBLE WEDNESDAY NIGHT...A FEW OF
WHICH MAY BECOME SEVERE. LOW CHANCES FOR THUNDERSTORMS EXIST
THROUGH THE REMAINDER OF THE PERIOD WITH NO ORGANIZED SEVERE
WEATHER THREAT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

IAZ044>050-057>062-070>075-301645-
CRAWFORD-CARROLL-GREENE-BOONE-STORY-MARSHALL-TAMA-AUDUBON-GUTHRIE-
DALLAS-POLK-JASPER-POWESHIEK-CASS-ADAIR-MADISON-WARREN-MARION-
MAHASKA-
1140 AM CDT TUE JUL 29 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED AFTERNOON AND EARLY EVENING THUNDERSTORMS ARE POSSIBLE
TODAY. AN ISOLATED SEVERE STORM OR TWO IS POSSIBLE WITH NICKEL
SIZED HAIL AND 60 MPH THE PRIMARY THREATS.

NUMEROUS RIVER FLOOD WARNINGS REMAIN IN EFFECT INCLUDING THE
NORTH...MIDDLE AND SOUTH RIVERS IN WARREN COUNTY AND AT SITES
ALONG THE RACCOON AND DES MOINES RIVER BASINS WITH MOST LOCATIONS
NEARING CREST.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

LOW CHANCES FOR THUNDERSTORMS EXIST THROUGH THE PERIOD WITH NO
ORGANIZED SEVERE WEATHER THREAT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

IAZ081>086-092>097-301645-
ADAMS-UNION-CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-
WAYNE-APPANOOSE-DAVIS-
1140 AM CDT TUE JUL 29 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED AFTERNOON AND OVERNIGHT THUNDERSTORMS ARE POSSIBLE
TODAY. AN ISOLATED SEVERE STORM OR TWO IS POSSIBLE WITH NICKEL
SIZED HAIL AND 60 MPH THE PRIMARY THREATS. LOCALLY HEAVY RAIN IS
POSSIBLE WHICH COULD AGGRAVATE ALREADY SATURATED CONDITIONS.

RIVER FLOOD WARNINGS REMAIN ALONG THE CHARITON RIVER WITH MOST
LOCATIONS NEARING CREST.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

SCATTERED THUNDERSTORMS ARE POSSIBLE ON WEDNESDAY WITH AN ISOLATED
SEVERE STORM POSSIBLE.

LOW CHANCES FOR THUNDERSTORMS EXIST THROUGH THE REMAINDER OF THE PERIOD
WITH NO ORGANIZED SEVERE WEATHER THREAT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

MOYER/DONAVON

The radar

The Des Moines radar (KDMX), 33 km away, was scanning. The volume nearest the first event began at 20:31 UTC.

Open the radar archive at this moment

Event by event

2 hail, 2 thunderstorm wind. Local standard time, as filed.

Hail, Story

When: July 29, 2:30 PM CST
Where: Story County, 0.86 mi SW of Ames
Measured: 1 in hail
Property damage: $1,000
Crop damage: $5,000
Reported by: Trained Spotter
Coordinates: 42.020, -93.630

Nickel to quarter size hail was reported.

Hail, Story

When: July 29, 2:36 PM CST
Where: Story County, 0.86 mi SW of Ames
Measured: 0.88 in hail
Crop damage: $5,000
Reported by: Law Enforcement
Coordinates: 42.020, -93.630

Thunderstorm Wind, Story

When: July 29, 2:37 PM CST
Where: Story County, 2.76 mi N of Ontario
Measured: 52 kt (60 mph) estimated gust
Property damage: $1,000
Reported by: Trained Spotter
Coordinates: 42.070, -93.680

Thunderstorm Wind, Story

When: July 29, 2:44 PM CST
Where: Story County, 0.69 mi S of Gilbert
Measured: 52 kt (60 mph) estimated gust
Property damage: $3,000
Reported by: Trained Spotter
Coordinates: 42.110, -93.650

Large tree 10 to 15 inches in diameter, along with power lines down in the town of Gilbert.

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.

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

The same day elsewhere

Every storm in Iowa in 2008 Every state in 2008 This day in weather history Warnings in Iowa, July 2008

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: 108369, 108370, 108371, 108400.