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

Temperature Profiles for Different Types of Precipitation

Freezing Drizzle• Drizzle drop: A drop of water with diameter 0.20.5

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 1994Roselawn, 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 http://www.pilotfriend.com/safe/safety/icing_conditions.htm

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

The Great Ice Storm of January 1998

2931 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

http://severewx.atmos.uiuc.edu/index.11.2002.html

2931 January 2002 Ice Storm

Photo © 2002 Brad Barrett

2931 January 2002 Ice Storm

Photo © 2002 Brad BarrettOkarche, Oklahoma