A strong low pressure system moved out of the southwest U.S. into Iowa during the overnight hours of the 19th through the day on the 20th.  A strong push of warm air took place.  The warm air was advected across cold air at the surface.  Over northern Iowa, the warm air was not able to scour out the low level cold air.  Moisture streamed north during the early morning hours of the 20th.  The atmosphere became somewhat unstable with elevated CAPE in the 500 to 1000 J/kg range.  A band of thunderstorms developing over central Iowa during the evening hours and lifted north into northern Iowa during the early morning hours.  As the storms moved north through central Iowa, brief heavy rain and half inch diameter hail occurred.  Over northern Iowa, a mixture of freezing rain, ice pellets, and occasional wet snow occurred.  Temperatures were close to freezing, thus not all of the freezing rain was realized as ice.  Reports of one quarter of an inch of ice accrual were received from several counties by the mid morning hours, though the area covered by the heavier ice accrual was spotty due to the nature of the thunderstorms.  The heaviest ice accrual took place in Emmet County with 1 inch of ice reported in Estherville.  Outside of Emmet County, some of the heaviest ice accrual took place southeast of Grafton in Worth County.  One half to three quarters of an inch of ice was reported there.  The ice only caused spotty power outages considering the widespread nature of the event.  Ice knocked out power to about 4000 customers over northern IA during the day, or about 2% of the grid was affected at some point in time.  Roads became very treacherous at the beginning of the event.  The roads were not a major problem by mid day as temperatures near the freezing point allowed for some melting on road surfaces.  As the area of precipitation lifted north, it became convective.  A thunderstorm moved through the Waterloo area.  Lightning struck a tree in Waterloo, sending part of the tree flying with pieces of bark breaking several windows in a house.  One fire was started due to the ice buildup.  Ice downed a power line onto a house in Clear Lake around 1700 CST.  The power line sparked and started a small fire.

Ice Storm in EMMET, IOWA
From 20-FEB-11 04:00:00 to 20-FEB-11 16:00:00 (CST-6)
Property damage: 25.00K
Crop damage: 0.00K
Reported by: COOP Observer

Ice Storm in KOSSUTH, IOWA
From 20-FEB-11 04:00:00 to 20-FEB-11 16:00:00 (CST-6)
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Utility Company

Ice Storm in WINNEBAGO, IOWA
From 20-FEB-11 05:00:00 to 20-FEB-11 17:00:00 (CST-6)
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Utility Company

Ice Storm in HANCOCK, IOWA
From 20-FEB-11 04:00:00 to 20-FEB-11 16:00:00 (CST-6)
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Public

Ice Storm in WORTH, IOWA
From 20-FEB-11 05:00:00 to 20-FEB-11 17:30:00 (CST-6)
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Utility Company

Lightning in BLACK HAWK, IOWA
From 20-FEB-11 07:15:00 to 20-FEB-11 07:15:00 (CST-6)
Location: WATERLOO
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Newspaper

Ice Storm in CERRO GORDO, IOWA
From 20-FEB-11 05:00:00 to 20-FEB-11 17:30:00 (CST-6)
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Official NWS Observations