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CLIMATE FACTORS HELPING TO SHAPE WINTER 2005-2006

Oct. 12, 2005 As winter 2005-2006 approaches, NOAA scientists say the leading climate patterns expected to impact winter weather are: the long-term climate trends, the North Atlantic Oscillation, or NAO, and the Madden-Julian Oscillation, or MJO.

Long-Term Climate Trends
In the absence of a significant El Niño and La Niña event, estimates of long-term trends along with a variety of dynamic and statistical tools provide the foundation for the forecast. One tool that is used at the NOAA Climate Prediction Center is the average conditions during the last 10 years compared with the long-term average for 1971-2000. Average winter temperature departures from normal for the period 1971-2000 are considerably cooler than those for the most recent 10-year average over much of the nation.

North Atlantic Oscillation (NAO)
The NAO is a major source of intra-seasonal variability over the United States, North Atlantic and Europe during the winter. The NAO modulates the circulation pattern over the middle and high latitudes, thereby regulating the number and intensity of significant weather events affecting the U.S.

The positive phase features a northward shift in the jet stream relative to its normal position. Associated with this phase is an increase in the occurrence of relatively warm days over the eastern two-thirds of the U.S. The negative phase features a southward shift of the jet stream. It is associated with an increase in more frequent cold air outbreaks and Nor'easters along the East Coast.

Madden-Julian Oscillation (MJO)
The MJO phenomenon is another factor likely to contribute to increased variability during the winter. The MJO influences the pattern of tropical rainfall, and produces El Niño/Southern Oscillation (ENSO)-like features on time scales of approximately 30-60 days (intra-seasonal). The MJO is most active during ENSO-neutral and weak-ENSO winters, and can influence the occurrence of extreme weather events, such as multiple day rain events and flooding along the Pacific Northwest Coast.

El Niño Southern Oscillation (ENSO)
Since early 2005, water temperatures in the central-equatorial Pacific Ocean have been near normal (ENSO-neutral). These conditions are expected to continue during this winter. As a result, it is unlikely that El Niño or La Niña will be a factor influencing the winter weather patterns. ENSO-neutral years often feature increased variability and increased occurrence of weather extremes in both temperature and precipitation for many areas of the country.

Implications for the U.S. in Winter 2005-2006

  • El Niño and La Niña are not likely to be factors influencing the winter weather in the United States;
  • The winter weather patterns during ENSO-neutral conditions are often dominated by other leading patterns of climate variability, including the Madden Julian Oscillation (MJO) and the North Atlantic Oscillation (NAO);
  • Currently, the occurrence of the NAO and its phase are difficult to anticipate more than one to two weeks in advance.

The NOAA Climate Prediction Center is one of nine National Centers for Environmental Prediction located in Camp Springs, Md. The NOAA Climate Prediction Center monitors and forecasts short-term climate fluctuations and provides guidance information on the long-term global effects climate patterns can have on the nation.

NOAA, an agency of the U.S. Department of Commerce, is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation's coastal and marine resources.

Relevant Web Sites
NOAA Climate Prediction Center

Media Contact:
Carmeyia Gillis, NOAA Climate Prediction Center, (301) 763-8000 ext. 7163