There were two days of hailstorms this week in Colorado, Ms. Walker said. On Tuesday "we got hit with a lot of hail very quickly, and that resulted more in flooding damage and also in hail damage as well," she said.

On Wednesday, the southwestern Denver area, as well as the nearby Golden and Lakewood regions, got hit very hard with hail. "Much of the Denver area got hit," Ms. Walker said. "It was very much the urban populations that saw the hail damage. We expect this to be the most expensive storm we've had in at least the last seven years."

Ms. Walker said the majority of the claims are auto claims, particularly those from Wednesday night because the hailstorm hit during commuting rush hours. "So we had a lot of dimpled cars and we also had losses from hail going through the windows. There were a lot of car dealerships that were hit?they got hit with hail with every car in their lot."

On the homeowners' side, there were a lot of roof damages. "We expect a lot of damages from homes and the roofs," Ms. Walker said.

Among the insurers facing the biggest potential for damage claims is the Bloomington, Ill.-based State Farm Insurance Companies, which has the biggest market share in Colorado, with about 22 percent of the auto and homeowners market, Ms. Walker said.

State Farm's initial estimates show it may have to pay 10,000 auto claims with a projected cost of $30 million and 7,500 property claims worth $26.3 million, according to the company. Others with big potential losses include Los Angeles-based Farmers Insurance Group, which has the second-largest market share in Colorado, followed by American Family Insurance Group in Madison, Wis., and Allstate Corp. in Northbrook, Ill.

"This will turn out to be the biggest storm loss in Colorado in quite some time," Ms. Walker said.