A weak inverted trough passed over the state during the day on the 20th.  Though the system was weak at the surface, the dynamics aloft were significant.  A strong upper level system moved across the Rockies into the central U.S. during the day.  Ahead of this feature, strong isentropic lift was in place.  In spite of the cold air at the surface, there was significant lift and moisture available in the 850 mb to 700 mb layer to produce precipitation.  Snow developed quite rapidly during the predawn hours of the 20th over western Iowa.  The snow spread east very quickly and in many cases became heavy within a few hours of inception.  Visibility was reduced to 1/4 to 1/2 mile during the heaviest snow with snowfall rates reaching 1 to 2 inches per hour in places.  Fortunately, there was little wind with this event.  Outside of drifting in open area, the snow caused relatively little trouble in spite of the band of 6 to 8 inch snowfall that occurred.  The snow band was 75 to 100 miles wide with the heaviest snow falling from near Estherville in the northwest, east-southeast to the Waterloo area.  Higher snowfall totals include 8 inches in Emmet County at Ringsted, and 7 inches in the Waterloo and Cedar Falls areas of Black Hawk County.  In Worth County, 7 inches was also measured in Manly.

Heavy Snow in GRUNDY, IOWA
From 20-JAN-12 06:00:00 to 20-JAN-12 16:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in HARDIN, IOWA
From 20-JAN-12 06:00:00 to 20-JAN-12 16:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in BREMER, IOWA
From 20-JAN-12 06:00:00 to 20-JAN-12 16:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in EMMET, IOWA
From 20-JAN-12 03:00:00 to 20-JAN-12 14:30:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in BLACK HAWK, IOWA
From 20-JAN-12 06:00:00 to 20-JAN-12 16:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in TAMA, IOWA
From 20-JAN-12 06:00:00 to 20-JAN-12 16:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in POCAHONTAS, IOWA
From 20-JAN-12 03:00:00 to 20-JAN-12 14:30:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in PALO ALTO, IOWA
From 20-JAN-12 03:00:00 to 20-JAN-12 14:30:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in BUTLER, IOWA
From 20-JAN-12 06:00:00 to 20-JAN-12 16:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in KOSSUTH, IOWA
From 20-JAN-12 03:00:00 to 20-JAN-12 14:30:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in HUMBOLDT, IOWA
From 20-JAN-12 03:00:00 to 20-JAN-12 14:30:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in WRIGHT, IOWA
From 20-JAN-12 03:00:00 to 20-JAN-12 14:30:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in WINNEBAGO, IOWA
From 20-JAN-12 03:00:00 to 20-JAN-12 14:30:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in WORTH, IOWA
From 20-JAN-12 06:00:00 to 20-JAN-12 16:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in CERRO GORDO, IOWA
From 20-JAN-12 06:00:00 to 20-JAN-12 16:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in HANCOCK, IOWA
From 20-JAN-12 03:00:00 to 20-JAN-12 14:30:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Heavy Snow in FRANKLIN, IOWA
From 20-JAN-12 06:00:00 to 20-JAN-12 16:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter