As clean-up continues from last weekend’s early snowstorm in the Northeast, insured losses already have exceeded $25 million, making this event a catastrophe.

PC360 reports that Verisk Analytics’ Property Claims Service has declared the storm as a catastrophe with insured losses exceeding $25 million in six states: Pennsylvania, New York, New Jersey, Connecticut, Massachusetts, and New Hampshire. Other areas are to be determined.

PC360 notes that claims from winter storms typically come in slowly since damage is normally seen after snow and ice melts, and after the lights come back on.

At one point about 4 million homes and businesses were without power as a result of the storm and electricity at some affected homes and businesses may be out until the end of the week. For this reason, PCS says it does not have a loss estimate available.”

Winter storms are historically very expensive and are the third-largest cause of catastrophe losses, behind only hurricanes and tornadoes. From 1991 to 2010, winter storms resulted in about $26 billion in insured losses, or more than $1 billion a year on average, according to ISO.

Insured U.S. winter storm losses in 2010 totaled $2.6 billion, the highest losses from this peril since 2003, according to a January 2011 analysis by Munich Re.