Iowa continued to be in a very unstable airmass with temperatures in the 80s and dew point temperatures well into the 70s.  A mesoscale vorticity maximum developed over the High Plains during the previous night and was located over northeast Nebraska during the morning of the 24th.  A complex of thunderstorms continued to move east into northwest Iowa.  As daytime heating continued, the storms became stronger and more organized.  The main product into the early afternoon hours was heavy rainfall.  During the early to mid afternoon hours, meso analysis clearly indicated the development of a surface low pressure system.  As the outflow, or meso cold front, dropped southeast into southern Iowa it encountered very rich air with dew points in the low 80s.  Thunderstorms developed explosively in central Iowa.  Within 15 to 20 minutes of initial development the storms became severe.  A tornado touched down in an open field in southern Polk County, about 5 miles south of West Des Moines.  The tornado was not well organized and did little damage.  Most of the storms that became severe produced high winds.  Winds of 65 MPH were reported in the Waterloo area.  One cell produced a wet microburst southeast of the city of Waterloo with winds around 80 MPH.  The high winds ripped the roof off of a house there, resulting in the house being toppled.  The storms left 2.29 inches of rain officially in the city, though some areas unofficially reported in excess of 8 inches.  Considerable urban flooding took place in the city of Waterloo, with flash flooding in the outlying areas.  Many basements were flooded as reports of standing water nearly 3 feet deep in the streets were received.  Earlier in the afternoon heavy rains fell in Webster City.  Upwards of 2 inches of rain fell in under an hour causing urban flooding in the city.  The water receded quickly after the rain stopped.  High winds were also reported in Story County in the Ames area.  A few reports of hail were received, but the hail was not all that large being as the freezing level was 15000 feet.  Nickle size hail fell in Waterloo and also in Windsor Heights.  After the initial fury of activity, the storms did not produce severe weather for a few hours.  As the storms continued to move east, they picked up in intensity again in the Ottumwa area.  Winds of 60 to 70 MPH blew through Ottumwa and continued east toward the Agency area.

Hail in POLK, IOWA
From 24-JUL-01 15:36:00 to 24-JUL-01 15:36:00 (CST)
Location: WINDSOR HGTS
Magnitude: 0.88 
Property damage: 3K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in WAPELLO, IOWA
From 24-JUL-01 18:36:00 to 24-JUL-01 18:36:00 (CST)
Location: OTTUMWA ARPT
Magnitude: 54 M
Property damage: 3K
Reported by: AWOS,ASOS,MESONET,ETC

Thunderstorm Wind in WAPELLO, IOWA
From 24-JUL-01 19:20:00 to 24-JUL-01 19:20:00 (CST)
Location: AGENCY
Magnitude: 61 E
Property damage: 10K
Crop damage: 2K
Reported by: LAW ENFORCEMENT

Flash Flood in BLACK HAWK, IOWA
From 24-JUL-01 15:00:00 to 24-JUL-01 17:00:00 (CST)
Location: WATERLOO
Property damage: 250K
Reported by: NEWSPAPER

Flood in HAMILTON, IOWA
From 24-JUL-01 13:00:00 to 24-JUL-01 15:00:00 (CST)
Location: WEBSTER CITY
Property damage: 25K
Reported by: NEWSPAPER

Hail in BLACK HAWK, IOWA
From 24-JUL-01 15:08:00 to 24-JUL-01 15:08:00 (CST)
Location: WATERLOO
Magnitude: 0.88 
Property damage: 3K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in BLACK HAWK, IOWA
From 24-JUL-01 15:13:00 to 24-JUL-01 15:13:00 (CST)
Location: ELK RUN HGTS
Magnitude: 57 E
Property damage: 10K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in STORY, IOWA
From 24-JUL-01 15:15:00 to 24-JUL-01 15:15:00 (CST)
Location: AMES
Magnitude: 52 E
Property damage: 3K
Reported by: AMATEUR RADIO

Thunderstorm Wind in BLACK HAWK, IOWA
From 24-JUL-01 15:20:00 to 24-JUL-01 15:20:00 (CST)
Location: WATERLOO
Magnitude: 69 E
Property damage: 50K
Crop damage: 10K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in STORY, IOWA
From 24-JUL-01 15:35:00 to 24-JUL-01 15:35:00 (CST)
Location: AMES
Magnitude: 52 E
Property damage: 10K
Reported by: EMERGENCY MANAGER

Tornado in POLK, IOWA
From 24-JUL-01 15:36:00 to 24-JUL-01 15:36:00 (CST)
Location: WEST DES MOINES
Tornado F-scale: F0
Crop damage: 1K
Reported by: AMATEUR RADIO

Brief touchdown in field south of town.