Extratropical cyclones (ETCs) are significantly more complex than tropical cyclone systems. Their primary energy source is not the warmth of ocean waters, as in the case of tropical cyclones, but rather the degree of contrast in temperatures between the poles and the equator. ETCs typically comprise several meteorological conditions that interact at once and in three dimensions including: high pressure ridges, low pressure troughs, weather fronts which separate air masses of contrasting temperatures, and the band of strong upper-level winds known as the jet stream. Because they tend to be most frequent during winter months, ETCs are often referred to simply as winter storms or, in extreme cases where frozen precipitation is involved, blizzards.

Numerical Weather Prediction

Because of their meteorological complexity, extratropical cyclones do not lend themselves to statistical parameterization and instead call for more physically-based modeling techniques. To that end, in 2000 AIR introduced a new approach—a first for the insurance industry—in its European Extratropical Model. It was the first probabilistic catastrophe model to incorporate numerical weather predication (NWP), an advanced technology used by all major meteorological agencies around the world.

NWP allows the complex time-dependent, three-dimensional structure of the damaging winds associated with these storms to be accurately represented—including the fine-scale features that are important for the strongest surface winds.

Winter Storms in the U.S.

AIR has continued to expand its capabilities in numerical modeling and in 2006 released the AIR U.S. Winter Storm Model—the first U.S. model to use NWP technology. The model simulates the separate and distinct footprints for damaging winds, precipitation, and freeze that typically characterize severe winter storms in the U.S. Because wind, precipitation and temperature damage property differently, AIR's winter storm model features damage functions that capture the specific mechanisms by which each of these storm components inflicts damage on property.

A Highly Realistic View of the Risk

Dr. Robert Fovell, Professor of Atmospheric and Oceanic Sciences at the University of California, Los Angeles, and a globally recognized expert in numerical modeling techniques, undertook a year-long peer review of AIR's approach to modeling extratropical cyclone hazard. According to Dr. Fovell, AIR "…combines NWP and stochastic techniques in a new way...a unique approach that results in a highly realistic view of the risk from extratropical cyclones."

AIR currently offers extratropical cyclone models for:

Listed below are additional materials of interest to companies exposed to extratropical cyclone, or winter storm, risk: