NOAA: El Niño to Help Steer U.S. Winter Weather
October 15, 2009
El Niño in the central and eastern equatorial Pacific
Ocean is expected to be a dominant climate factor that
will influence the December through February winter
weather in the United States, according to the 2009 Winter
Outlook released today by NOAA’s Climate Prediction
Center. Such seasonal outlooks are part of NOAA’s suite of
climate services.
“We expect El Niño to strengthen and persist through
the winter months, providing clues as to what the weather
will be like during the period,” says Mike Halpert, deputy
director of the Climate Prediction Center – a division of
the National Weather Service. “Warmer ocean water in the
equatorial Pacific shifts the patterns of tropical
rainfall that in turn change the strength and position of
the jetstream and storms over the Pacific Ocean and the
U.S.”
“Other climate factors are also likely to play a role
in the winter weather at times across the country,” added
Halpert. “Some of these factors, such as the North
Atlantic Oscillation are difficult to predict more than
one to two weeks in advance. The NAO adds uncertainty to
the forecast in the Northeast and Mid-Atlantic portions of
the country.”
Highlights of the U.S. Winter Outlook (December
through February) include:
-
Warmer-than-average temperatures are
favored across much of the western and central U.S.,
especially in the north-central states from Montana to
Wisconsin. Though temperatures may average warmer than
usual, periodic outbreaks of cold air are still
possible.
- Below-average temperatures are
expected across the Southeast and mid-Atlantic from
southern and eastern Texas to southern Pennsylvania and
south through Florida.
- Above-average precipitation is
expected in the southern border states, especially Texas
and Florida. Recent rainfall and the prospects of more
should improve current drought conditions in central and
southern Texas. However, tornado records suggest that
there will also be an increased chance of organized
tornado activity for the Gulf Coast region this winter.
- Drier-than-average conditions are
expected in the Pacific Northwest and the Ohio and
Tennessee River Valleys.
- Northeast: Equal chances for
above-, near-, or below-normal temperatures and
precipitation. Winter weather in this region is often
driven not by El Niño but by weather patterns over the
northern Atlantic Ocean and Arctic, such as the North
Atlantic Oscillation. These patterns are often more
short-term, and are generally predictable only a week or
so in advance.
- California: A slight tilt in the
odds toward wetter-than-average conditions over the
entire state.
- Alaska: Milder-than-average
temperatures except along the western coast. Equal
chances for above-, near-, or below-median precipitation
for most areas except above median for the northwest.
- Hawaii: Below-average temperatures
and precipitation are favored for the entire state..
This seasonal outlook does not predict where and when
snowstorms may hit or total seasonal snowfall
accumulations. Snow forecasts are dependent upon winter
storms, which are generally not predictable more than
several days in advance.
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