Recent rumors that Western Washington is in for its severest winter in 50 years are nothing more than unsupported hype that goes well beyond current forecast abilities, according to University of Washington atmospheric scientists.
Some of the rumors, sent by e-mail and citing official-sounding sources, include completely false statements and assumptions about effects from the current La Ni?n the equatorial Pacific Ocean, said Philip Mote, a UW research scientist with the Joint Institute for the Study of Atmosphere and Ocean.
Among them is the claim that from late December through March, high temperatures will be in the upper 30s and lows will be in the upper 20s, with frequent, heavy snowfall that will not melt and potentially will accumulate to 100 inches. Such conditions never have been recorded in the Puget Sound area, Mote said, and temperatures rarely stay that low for more than a week, certainly not for three months.
In the last 104 years, there have been only six occasions when the average temperature for an entire month was below freezing, most recently in January 1969.
“These are things that have never happened during the last century. That’s what makes it so outrageous,” said UW atmospheric sciences professor Cliff Mass.
Perhaps the most flagrant contention is that the region will experience weeks or more of below-zero temperatures. If that claim refers to the Celsius scale, on which zero is the freezing point of water, such prolonged temperatures are very unlikely, Mote said. If it refers to the Fahrenheit scale more familiar to the public, the claim is absolutely wrong. Seattle has never recorded a temperature below zero on the Fahrenheit scale.
“While it is always a good idea to be prepared for natural disasters, this forecast is irresponsible hype,” Mote said. “The best scientific forecasts for the coming winter are based on elaborate computer models and on the connection between conditions in the tropical Pacific and middle latitudes.”
La Ni?efers to a set of climate anomalies in the tropical Pacific that brings unusually strong trade winds and exceptionally heavy rainfall in normally rainy areas near the western Pacific. In many ways, climate anomalies associated with La Ni?re opposite those of El Ni?P>In the Northwest, Mote said, La Ni?enerally means a higher probability of cold winter temperatures; average or above-average rainfall, especially west of the crest of the Cascade Mountains; and average or above-average snowpack in the Cascades and Olympics. It also typically means significant snowfall in low-lying urban areas that usually melts within a week; heavily saturated soils and a higher risk of landslides; and extreme precipitation and river flooding.
People should prepare for a snowy winter, Mote said, “but I wouldn’t recommend spending lots of money doing so – buying a four-wheel-drive vehicle or a snowplow, for example.”
Climatologists cite 1949-50 and 1968-69, when Seattle received about 60 inches of snow, as the worst winters. Snow depths never exceeded 20 inches, but snow was on the ground for most of January. The winter of 1949-50 was the severest this century in Western Washington, but the 1968-69 winter produced the state’s cold-temperature record of 48 degrees below zero Fahrenheit in Winthrop and Mazama.
Mass said this winter probably will be somewhat colder than normal, with slightly more rain and snow, but the difference will be in inches, not feet. The Seattle area normally receives about 12 inches of winter snow, and that increases to about 17 inches in La Ni?ears, he said.
“I think it’s important for people to understand that we’re not necessarily expecting a severe winter. It probably will be colder than last winter, which was rather benign,” Mass said. “People are likely to notice a change, but it’s not going to be the end of the world.”
More details about the rumors and UW scientists’ response can be found at http://tao.atmos.washington.edu/PNWimpacts/LaNina.html.