UPDATE 2-U.S. winter likely to continue hot weather trend

Thu Oct 18, 2012 3:17pm EDT

* Drought could continue and spread, US forecasters say
    * Coming season could be warmest in 118 years
    * An elusive El Nino challenges government predictions


    By Deborah Zabarenko and Ayesha Rascoe
    WASHINGTON, Oct 18 (Reuters) - After a hot spring and a
scorching summer, this winter is likely to continue a U.S.
warming trend that could make 2012 the hottest year since modern
record-keeping began, U.S. weather experts said Thursday.
    Drought that ravaged much of the United States this year may
spread in the coming months, said Mike Halpert at the National
Oceanic and Atmospheric Administration's Climate Prediction
Center.
    "The large majority of that drought we expect to persist,"
Halpert said. "We even see drought expanding westward ... into
Montana, Idaho and part of Oregon and Washington."
    Dryer-than-usual winter weather is expected in much of the
Pacific Northwest, with higher-than-normal precipitation
predicted for the Gulf Coast, according to NOAA forecasts.
    For much of the country, a three-month
(December-February)winter forecast is hard to pin down. The vast
majority of states have what the experts said was an equal
chance of below-normal, normal or above-normal precipitation.
    The densely populated East Coast, along with the southern
tier of states from Texas to Florida and the upper Midwest also
have an equal chance of colder, normal or warmer weather this
winter, according to the forecasters.
    Still, there is enough data to predict a warm winter
overall, said Deke Arndt, chief of climate monitoring at NOAA's
National Climatic Data Center. The first nine months of 2012
were the warmest of any year on record in the contiguous United
States, and this has been the third-hottest summer since
record-keeping began.
    "The main issues facing the U.S. going into this (winter)
outlook period stem from persistent heat and drought," Arndt
said at a telephone briefing. "It is likely that 2012 will be
the warmest of the 118-year record for the contiguous United
States."
    An El Nino pattern -- a recurring patch of warmer than usual
water in the equatorial Pacific that can have a potent effect on
U.S. weather -- gave hints of developing in September but then
subsided, the first time this has happened in approximately 60
years of record keeping on this phenomenon, Halpert said.
    "This is one of the most challenging outlooks we've produced
in recent years because El Nino decided not to show up as
expected," he said.
    A record-warm winter would be in line NOAA's latest report
on global temperatures, which found September 2012 tied for the
hottest September in world records going back to 1880.
    However, Arndt said that the signal of human-spurred climate
change is less apparent now in some U.S. regions, especially in
winter. This is due in part to the changing baseline forecasters
use.
    U.S. government experts look back 30 years to figure out
baseline temperatures for the country. In the past, they used
the 30-year period from 1971 through 2000; this year, they used
1981 through 2010. That latest period shows little sign of a
warming trend in areas like Florida and other parts of the
southeast, Arndt said.
    That updated baseline helps to "mask" the signs of climate
change on a regional and seasonal basis, Arndt said.
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