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NOAA Issues Nation's Official Winter Forecast:
Lingering La Niña Will Shape Weather Patterns
Warm and Dry in South and Southwest; Snow/Rain to Northwest and Great Lakes;
Jet Stream Guides Fate of North Central States and Northern New England

La Niña - 10-26-99October 26, 1999 — The nation's top climate and weather experts of the National Oceanic and Atmospheric Administration today unveiled the winter weather forecast for the United States, saying that a lingering La Niña climate cycle of cold tropical Pacific waters will influence wintertime weather patterns through March.
(Click here to see animation of La Niña.) (Click here for more graphics.)

"Once again, La Niña will have a pronounced effect on winter weather in the United States and, consequently, many climate-sensitive businesses and industries," said D. James Baker, under secretary of commerce for oceans and atmosphere and NOAA administrator. "While we can't put a price tag on this year's La Niña cycle, we can forecast with confidence how it will steer the nation's winter weather."

"La Niña will alter the strength and pattern of the Pacific jet stream over North America to give us a warm and dry winter in the southern half of the nation, but more snow and rain to the Pacific Northwest and the Great Lakes. We expect considerable month-to-month variation in temperature, rainfall and storminess in the central, northern and eastern states, which means days of warmer than normal temperatures followed by bouts of bitter cold. As with every winter, it's too early to predict just how the jet stream will affect the weather in many north central states and for northern New England," said Baker.

Baker pointed out that an increasing number of weather sensitive businesses and industries use NOAA's climate outlooks to base long-term business decisions. For example, city managers may use these forecasts in purchasing adequate amounts of road salt for snow removal systems in their public works departments. In addition, farmers may use the forecasts to select and time the planting of crops that can better withstand a given climate cycle. According to recent Commerce Department/NOAA studies into the economic impacts of La Niñas and El Niños, the weather-sensitive industries of agriculture, recreation, construction, energy distribution, and water management accounted for a combined 15 percent of the nation's gross domestic product.

"The cycling between the warmer El Niños and colder La Niñas can alter temperatures and rains to such an extent that they significantly disrupt U.S. agriculture, commercial fishing, tourism, and many diverse businesses and industries," said Baker. "We're finding that last winter's La Niña may cause U.S. agricultural losses of more than $2 billion, which tops the $1.5 billion in agricultural damage from the 1997-98 El Niño cycle. In addition, the 1997-98 El Niño that brought a mild winter to the northern Midwest and heavy rains to the Southwest and West Coast caused U.S. energy consumers to spend $2.2 billion less on oil and gas for heating, but then cost consumers and farmers $3 billion in lost crops and agricultural production."

"Over the past decade, we have improved the forecasting of La Niña and El Niño so that we can now predict these events and their expected climatic impacts on different regions with some 70 to 80 percent accuracy a year before they occur," said John J. Kelly Jr., director of NOAA's National Weather Service.

"In each of the past two years, the National Weather Service's climate forecasts for the winter have been made with record skill. We're now able to accurately forecast an impending La Niña or El Niño cycle months in advance instead of detecting them as they reach their peaks," said Kelly. "NOAA produces its winter weather forecast with confidence because of gains in climate system research and advances in our computer modeling capabilities. In addition, NOAA installed more than 70 buoys that, via NOAA satellites, feed real time ocean and atmosphere data into sophisticated computer models to produce climate forecasts that are unprecedented."

Officials say it is not just long-term climate forecasting that has improved their ability to predict winter weather.

"NOAA's National Weather Service has also improved the agency's ability to predict and track winter storms at the local level," said Kelly. "The $4.5 billion modernization of National Weather Service technologies has provided advanced capabilities in delivering accurate and timely forecasts and warnings prior to winter storms. Meteorologists in every forecast office now use new work stations to combine the latest Doppler radar observations with satellite data and sophisticated computer models to produce more immediate and precise forecasts and warnings than ever before. This new combined technology saves time and, ultimately, lives."

Officials say the improved radar technology and early warning system helped local governments in Washington, D.C. brace for the impending snowstorm of

January 6-8, 1996. The weather service issued warnings days before the major snow storm, whereby the Virginia Department of Transportation prepared four days in advance and the state's governor declared a state of emergency before the first snow flake fell.

La Niña winters are characterized by temperature variability, or changes in the weekly mean temperatures as the season progresses. A season with little variability would have mean temperatures that changed little from week to week. A season with high variability, like this La Niña, will have some very warm weeks interspaced with some very cold ones.

"La Niña years are characterized by a tendency for blocking high pressure systems to form in the North Pacific Ocean. These blocks tend to persist for a week or two at a time. Depending on the exact location, which is variable, the weather can alternate from very warm to very cold conditions that persist for a while, then change. This causes the large amount of temperature variability in the northern United States," said Louis Uccellini, director of the National Weather Service's National Centers for Environmental Prediction, a NOAA facility in Camp Springs, Md.

NOAA climate experts also point to other factors that pose a particular challenge to forecasters. One such factor that acts independently of a La Niña event is the North Atlantic Oscillation cycle. The oscillation produces a large scale change in the jet stream that causes weather patterns to fluctuate and temperatures and precipitation to vary widely.

Winter Weather Breakdown by Temperature & Precipitation:
Alaska: Colder and drier than normal.
Hawaii: Colder and wetter than normal.
Pacific Northwest: Above-normal precipitation and increased storminess. Near-normal seasonal temperatures overall.
California: Below-normal temperatures near coast. Above-normal precipitation in the north and below-normal precipitation in the south.
Southwest: Above-normal temperatures, below-normal precipitation.
Northern Plains: Near-normal seasonal temperatures and above-normal precipitation. Significant arctic outbreaks likely.
Rocky Mountain Region: Near- to above-normal temperatures, above-normal precipitation in the north to below-normal precipitation in the south.
Midwest: Near- to above-normal temperatures as you go from north to south, above- normal precipitation entire region.
New England: Warmer than normal in southern New England; jet stream makes prediction uncertain for northern New England.

Southern Tier from Texas through Florida and the Southeast: Warmer and drier than normal, with dryness most likely in New Mexico, South and West Texas, and Florida.
Mid-Atlantic States: Milder than normal with near-normal precipitation east of the Appalachians.
Ohio and Tennessee River Valleys: Warmer and wetter than normal. Increased number of heavy precipitation events and an increased risk of severe winter weather.
Great Lakes and Northeast: High degree of uncertainty at this time. Considerable variability from week to week with the average of above-normal temperatures in southern areas and closer to normal in the north. Near-normal precipitation south and east of the Appalachians, and above normal elsewhere.

Snowfall above normal:
Ohio and Tennessee River Valleys
Pacific Northwest, especially higher elevations
Upper Midwest and northern Great Lakes

Snowfall below normal:
eastern New Mexico
northern Texas
central Oklahoma

For more detail on the winter weather outlook and information about La Niña, go to NOAA's Climate Prediction Center Web site at

The Winter Weather Awareness site of NOAA's National Weather Service is found at

More information about NOAA's National Weather Service and its products and services are found at the agency's main Web site

La Niña sea-surface temperature animation is available at:

Still images of La Niña sea-surface temperature anomalies are available at: