Ice Storm in Iowa, February 11, 1999

A very vigorous storm system moved through the central U.S. during the morning of the 11th. Very warm and moist air was drawn north ahead of the system with record high temperatures in the 60s reported. Dew point temperatures soared into the mid to upper 50s as well. A wide variety of weather was associated with the storm. Thunderstorms were reported over much of the state, with significant storms including hail over the southeast third of Iowa. The problem was that in the wake of the surface low pressure system, a cold front passed through the state. Temperatures fell as much as 20 to 30 degrees in an hour or so after the frontal passage. Much of the state fell to freezing or below by daybreak on the 11th. The thunderstorms then moved over sub-freezing air to produce freezing rain. Further to the northwest there were no thunderstorms, however rain fell into areas where the surface temperature had fallen into the upper 20s. Travel was hazardous with some areas receiving over one quarter inch of ice. Significant ice accretion occurred over parts of northwest Iowa. In the Graettinger area of Palo Alto County, ice accumulated on trees which fell taking out power in the area for 7 hours. Most locations received little more than a tenth inch of ice cover however. There was some minor damage to trees around the area due to the wind and ice loading, but the most significant problem was with icy travel. Spotty power outages were also reported due to "galloping transmission lines", which is caused by ice accretion changing the aerodynamics of the lines such that they form an air foil in the wind. During the afternoon hours it became cold enough to change the freezing rain to snow. A band of snow moved across the state. The snow combined with winds of 30 to 40 MPH produced blizzard conditions for a brief period as the band moved through. Several roads were closed including Interstate 35 north of U.S. Highway 30 and Iowa State Highway 44 in Dallas County. The band of near zero visibility only lasted one to two hours and conditions improved rapidly during the evening. Many schools across the state closed early during the afternoon of the 11th, and most events across the state were cancelled that evening. THere were hundreds of accidents reported across the state due to the icy roads. Rush hour traffic was a major problem in the larger cities such as Des Moines. The ice lingered into the next day, but at least the visibility had improved.