Multiple outbreaks of severe weather led to a costly month for insurers in the United States in May, as thunderstorm events continued to dominate the catastrophe record.

According to the latest Global Catastrophe Recap report by Aon Benfield’s Impact Forecasting, no fewer than four stretches of severe weather affected the U.S. during the month of May.

Aggregate insured losses exceeded $2.2 billion and overall economic losses were at least $3.5 billion, with large hail and damaging winds the primary driver of the thunderstorm-related costs, Impact Forecasting reports.

The costliest stretch occurred during a five-day period (May 18-23) which saw damage incurred in parts of the Midwest, Plains, Rockies, Mid-Atlantic and the Northeast, including the major metropolitan areas of Chicago, IL and Denver, CO.

According to Impact Forecasting’s report, baseball-sized hail and straight-line winds gusting in excess of 70 mph (110 kph) were recorded that severely affected residential, commercial and auto interests. Total economic losses were estimated at $2.5 billion, with insurers reporting losses minimally at $1.5 billion.

Meanwhile, the combination of excessive heat, extreme drought conditions, low relative humidity and gusty winds led to dozens of wildfires across parts of the Texas Panhandle and Southern California, leaving two dead.

Overall fire costs/damages from the two states approached $100 million, according to Impact Forecasting.

In Texas the most significant fire was in Hutchinson Country, where at least 225 homes and 143 unoccupied structures were damaged or destroyed.

In California, at least 14 fires were ignited in the greater San Diego metropolitan region, including the Poinsettia Fire that destroyed eight homes, an 18-unit condominium complex, and two commercial buildings.

The report adds that through the end of May, tornado activity in the U.S. remained in the bottom 25th percentile of all years dating to the early 1950s.

Check out I.I.I. facts and statistics on thunderstorms.