A very strong upper level trough of low pressure developed over the western U.S. during the mid part of the week.  Strong south winds in the low levels drew considerable moisture north into the central U.S.  Dew points reached the upper 60s to low 70s during the early morning of the 29th.  Surface low pressure lifted northeast into the Dakotas during the afternoon and evening hours.  A dry line extended south from the slow and pushed into western Iowa during the afternoon hours.  The atmosphere was quite unstable for late October with lifted indices around -3 C. and CAPE values in the 1000 to 2000 J/kg range over much of the state.  The freezing level was around 13,300 feet, which limited the amount of hail from the storms.  Thunderstorms formed initially along the dry line during the mid to late afternoon hours.  A secondary line formed ahead of the main line by late afternoon and itself produced severe weather.The primary line lifted northeast at over 50 MPH across the state during the early evening hours.  Several of the storms did produce some hail of three quarter to one inch in diameter.  Hail of one and one quarter inch in diameter fell in Butler County.  During the afternoon, a strong jet segment lifted northeast into the central U.S. with 100 kt winds reported in the jet streak.  The principle mode of severe weather was high winds.  There were several reports of 60 to 65 MPH winds.  Nearly all of the storms produced gusty winds of at least 40 to 50 MPH.

Hail in POWESHIEK, IOWA
From 29-OCT-04 17:39:00 to 29-OCT-04 17:39:00 (CST)
Location: GRINNELL
Magnitude: 0.88 
Property damage: 2K
Crop damage: 1K
Reported by: AMATEUR RADIO

Thunderstorm Wind in BREMER, IOWA
From 29-OCT-04 18:35:00 to 29-OCT-04 18:35:00 (CST)
Location: PLAINFIELD
Magnitude: 57 EG
Property damage: 10K
Reported by: GENERAL PUBLIC

Hail in BUTLER, IOWA
From 29-OCT-04 18:38:00 to 29-OCT-04 18:38:00 (CST)
Location: GREENE
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Thunderstorm Wind in POLK, IOWA
From 29-OCT-04 18:04:00 to 29-OCT-04 18:04:00 (CST)
Location: ANKENY
Magnitude: 50 MG
Property damage: 1K
Reported by: AWOS,ASOS,MESONET,ETC

Thunderstorm Wind in POWESHIEK, IOWA
From 29-OCT-04 17:39:00 to 29-OCT-04 17:39:00 (CST)
Location: GRINNELL
Magnitude: 52 EG
Property damage: 2K
Reported by: AMATEUR RADIO

Thunderstorm Wind in POLK, IOWA
From 29-OCT-04 17:40:00 to 29-OCT-04 17:40:00 (CST)
Location: WINDSOR HGTS
Magnitude: 52 EG
Property damage: 2K
Reported by: NWS EMPLOYEE(OFF DUTY)

Thunderstorm Wind in JASPER, IOWA
From 29-OCT-04 17:20:00 to 29-OCT-04 17:20:00 (CST)
Location: REASNOR
Magnitude: 50 EG
Property damage: 10K
Reported by: TRAINED SPOTTER

Hail in STORY, IOWA
From 29-OCT-04 16:52:00 to 29-OCT-04 16:52:00 (CST)
Location: ZEARING
Magnitude: 0.88 
Property damage: 2K
Crop damage: 1K
Reported by: TRAINED SPOTTER

Hail in STORY, IOWA
From 29-OCT-04 16:41:00 to 29-OCT-04 16:41:00 (CST)
Location: NEVADA
Magnitude: 0.88 
Property damage: 2K
Crop damage: 1K
Reported by: AMATEUR RADIO

Hail in BUTLER, IOWA
From 29-OCT-04 18:40:00 to 29-OCT-04 18:40:00 (CST)
Location: GREENE
Magnitude: 1.25 
Property damage: 5K
Crop damage: 1K
Reported by: GENERAL PUBLIC

Thunderstorm Wind in BUTLER, IOWA
From 29-OCT-04 18:40:00 to 29-OCT-04 18:40:00 (CST)
Location: GREENE
Magnitude: 61 EG
Property damage: 5K
Reported by: GENERAL PUBLIC