Wednesday, January 17, 2007

Ice Storm in January

doppler radar image from Monday

The ice storm hit the U.S. hard, in a broad swath from Texas in the southwest to Maine in the northeast. As of today, the statistics are grim: 55 people dead in 9 states and 300,000 still without electricity. The storm had been predicted and warnings were posted but some things are out of our control. Tree limbs fell, no longer able to support the one-inch casing of ice building on them, causing many of the outages and falling on buildings. Overhead wires and supporting poles, unable to hold up under the growing load, leaned and buckled. The only saving grace was it happened on a holiday, Martin Luther King Jr. Day, and fewer people were on the road than a typical Monday.

My local area was little affected and we feel very lucky to have dodged a bullet. We had a variety of precipitation, combining rain, sleet, snow, and rain into a layered sandwich but none or little of the ice build-up of freezing rain. Counties north of Albany were encased in ice and continue to have problems, as are many areas of the country.

So why did this happen? Most people are blaming global warming but there is a primary cause for this particular storm: El Niño.

satellite image from Monday

What is El Niño and what causes it? From the National Oceanic and Atmospheric Administration (NOAA):
El Niño results from interaction between the surface layers of the ocean and the overlying atmosphere in the tropical Pacific. It is the internal dynamics of the coupled ocean-atmosphere system that determine the onset and termination of El Niño events. The physical processes are complicated, but they involve unstable air-sea interaction and planetary scale oceanic waves. The system oscillates between warm (El Niño) to neutral (or cold) conditions with a natural periodicity of roughly 3-4 years.
The size and location of the large pool of warm water called El Niño varies from year to year. California typically receives 18-20 inches of rain in a year, most of it in the winter. Storms out of Alaska bathe the coast and drop snow in the Sierras. When El Niño is large and in a northern area, it drives the storms north and away from the state, setting up drought conditions. The size and location of El Niño has a significant effect on winter weather in California.

The picture above shows clouds streaming from the Southwest to the Northeast. If you track back from the U.S. through Mexico and into the Pacific Ocean, the origin would be pointing to El Niño. I don't know if global warming is a cause or contributor, but I never expected El Niño to influence weather in New York and the East.