FACTORS HELPING TO SHAPE WINTER 2005-2006
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.
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.
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.
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.
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.
for the U.S. in Winter 2005-2006
Niño and La Niña are not likely to be factors influencing
the winter weather in the United States;
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);
the occurrence of the NAO and its phase are difficult to anticipate
more than one to two weeks in advance.
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.
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
Carmeyia Gillis, NOAA
Climate Prediction Center, (301) 763-8000 ext. 7163