FACTORS HELPING TO SHAPE WINTER 2004-2005
6, 2004 ó As Winter 2004-2005 approaches, NOAA scientists say the leading
climate patterns expected to impact winter weather are: the El Niño/Southern
Oscillation, the North Atlantic Oscillation, the Pacific/North American
pattern and long-term climate trends. Scientists at the NOAA Climate
Prediction Center say these patterns are the physical basis for this
season's winter outlook.
Niño Southern Oscillation (ENSO)
Water temperatures in the central-equatorial Pacific Ocean are warmer
than average, indicating the early stages of a warm (El Niño)
episode. Current departures indicate that the intensity of this episode
is weak. Most sea-surface temperature forecasts indicate that El Niño
will continue through early 2005. Considering the sea surface temperature
predictions, the time of year and the observed oceanic and atmospheric
circulation patterns, the intensity of any warming is expected to be
weak, or potentially moderate.
years, scientists say, tend to be associated with the positive phase
of the Pacific/North American pattern.
American (PNA) Pattern
The PNA pattern features changes in the strength and position of the
jet stream and storminess over the eastern North Pacific and North America.
The positive phase of the PNA is often associated with weak El Niño
weak El Niño episodes, the jet stream is stronger-than-average
over the east-central North Pacific and over the Mid-Atlantic States,
with greater-than-average storminess in the Aleutians/Gulf of Alaska
and along the southeast coast of the United States. This results in
warmer and drier than average conditions over western North America
and cooler and wetter than average conditions over the Southeast United
Atlantic Oscillation (NAO)
The NAO is a major source of variability over the United States, North
Atlantic and Europe during winter. It modulates the circulation pattern
over the North Atlantic and North America regions, thereby regulating
the number and intensity of significant weather events affecting the
U.S. During the winter, it can often flip flop between its positive
phase and its negative phase.
phase features a jet stream shifted to the north of its normal position
along the U.S. East Coast. Associated with this phase is an increase
in the number of extreme warm days over much of the contiguous United
phase features a shift in the jet stream southward along the U.S. East
Coast resulting in an increased number of extreme cold days, especially
from the Great Plains to the Southeast.
Long-Term Climate Trends
In the absence of significant forcing by the leading patterns of natural
climate variability (i.e. ENSO, NAO), estimates of decadal trends provide
the basis for the forecast. One tool that is used at the NOAA Climate
Prediction Center is the average conditions during the last 10 years
compared to the long-term average for 1971-2000.
for the U.S. in Winter 2004-2005
ENSO episodes are often associated with the positive phase of the
PNA pattern favors a southward shift in the jet stream and storm track
toward the southeastern United States, which leads to cooler and wetter
than average conditions across large portions of the South;
PNA also favors above normal temperatures over Alaska, and the western
unpredictability of the seasonal phase of the NAO introduces uncertainty
in the seasonal outlook, especially in the Northeast U.S.;
negative phase of the NAO is associated with relatively frequent Nor'easters
and heavy lake effect snows in the Northeast and Midwest, and also
cold air outbreaks into the deep South. Currently, researchers can
only forecast the phase of the NAO out to 5 to 10 days, which results
in some uncertainty in the seasonal outlook.
on the Weather Prediction Front
The NOAA Hydrometeorological Prediction Center Winter
Weather Desk products and services are being expanded this year.
For the past three winters, the HPC and the NOAA National Weather Service
field offices conducted Winter Weather Experiments to examine new approaches
to forecasting and collaboration on potential life-threatening winter
weather across the U.S. As a result of these experiments, new winter
weather products—involving the prediction of snowfall amounts
and winter storm tracks—will be available to forecast offices
and the public. Also, a refined collaborative forecast process has resulted
that involves the HPC and the NWS forecast offices. The goal of the
Winter Weather Desk is to combine the winter weather forecasting expertise—at
the national and local levels—and bring greater geographic consistency
and improved accuracy with NOAA Weather Service local forecasts, watches
and warnings to the public.
the CPC and HPC
The Climate Prediction Center and the Hydrometeorological Prediction
Center, located in Camp Springs, Md., are two of nine NOAA National
Centers for Environmental Prediction. The Climate Prediction Center
serves the public by assessing and forecasting the impacts of short-term
climate variability, emphasizing enhanced risks of weather-related extreme
events, for use in mitigating losses and maximizing economic gains.
The Hydrometeorological Prediction Center provides nationwide analysis
and forecast guidance products out through seven days.
NOAA 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 nationís coastal and marine resources. NOAA is part
of the U.S. Department of Commerce.
Relevant Web Sites
Climate Prediction Center
Hydrometeorological Prediction Center
Winter Weather Forecasts
Niño/Southern Oscillation (ENSO) Diagnostic Discussion
El Niño/Southern Oscillation (ENSO) Update
Recent 2 Months Sea Surface Temperature Anomaly Animation
Niño and La Niña-related Winter Features over North America
Surface Temperature Outlook
Impacts by Region
Gillis, NOAA Climate Prediction
Center, (301) 763-8000 ext. 7163