Ice Storms

Why Study Ice Storms? Ice accumulation can: –cause extensive power outages –halt air and ground transportation –cause considerable property damage Aircraft Icing Huge socioeconomic impact in affected areas

NWS Criteria –An ice storm is characterized by significant ice accumulations (¼” or greater) –An ice storm warning is issued when freezing rain is expected to produce a significant (> ¼”) and possibly damaging accumulation of ice. Ice storms often produce structural damage Ice Storms

Supercooled Water Water does not always freeze at 0°C –But ice does begin to melt at 0°C Pure water will not spontaneously freeze until –40°C. Brr!! To freeze, water molecules need ice nuclei –Promote freezing at temps below –15°C –Hardly effective in clouds between –5° and 0°C –Few available ice nuclei results in supercooled water droplets Supercooled water droplets will freeze on contact with a surface that is colder than 0°C

Temperature Profiles for Different Types of Precipitation

Freezing Drizzle Drizzle drop: A drop of water with diameter 0.2  0.5 mm falling usually (but not always) from low stratus or stratocumulus (layered) cloud; also called mist Freezing drizzle: –Falls from shallow clouds with tops no cooler than about  10°C –Drops grow by colliding and coalescing with other drops –Freezes on contact with surfaces that are cooler than 0°C –Causes glazing problems Big problem for aircraft –As planes ascend or descend through shallow stratiform clouds, freezing drizzle can accumulate on wings and nose, reducing lift

31 October 1994 Roselawn, IN Flight on approach to Chicago’s O’Hare Airport went down while in a holding pattern Freezing drizzle accumulated on wings Plane lost lift For flight safety tips on icing conditions, visit

Weather Patterns Associated with Freezing Precipitation

Freezing Rain Climatology

Freezing Drizzle Climatology

Freezing Rain Sounding

The Great Ice Storm of January 1998 Record high of 65°F in New York City on January 8 Temperatures at the summit of Mount Washington (6288 ft) were well above freezing, while the valley below (~200 ft) suffered Extremely cold temperatures followed the storm

The Great Ice Storm of January 1998

29  31 January 2002 Ice Storm Oklahoma, Kansas, Missouri, Illinois and Indiana all were affected Ice accumulations of 1 to 3 inches in Oklahoma –>200,000 without power –OG&E costs exceeded $100 million

29  31 January 2002 Ice Storm Photo © 2002 Brad Barrett

29  31 January 2002 Ice Storm Photo © 2002 Brad Barrett Okarche, Oklahoma