Weather Watch:  August 2004

LONG-TERM DROUGHT IN THE U.S.

As of mid March 2004, Arizona's Lake Powell, holding back the Colorado
River at the Glen Canyon Dam, was 42% of capacity, stranding most of
the marinas and exposing 115 feet of canyon walls long hidden by the
lake's water.  With the Colorado River Basin in the fifth year of a
drought, what are the prospects for relief?

A recent study by Gregory McCabe of the U.S. Geological Survey and
colleagues suggests the recent drought is controlled by three factors:
a 20-30-year cycle of sea-surface temperature in the Pacific, a
60-70-year cycle of sea-surface temperature in the Atlantic, and a
factor that looks like the rising average temperature in the Northern
Hemisphere.  If past historical climate patterns repeat, their results
suggest two possible scenarios are likely to occur in the future.  One
scenario will be similar to the 1930s droughts that struck the Pacific
Northwest and the central U.S.  The other scenario will be similar to
the drought in the 1950s that affected much of the southwest U.S.  In
either case, although years with occasional normal or above normal
precipitation may occur, as long as North Atlantic sea-surface
temperatures remain warm there is a possibility that below normal
rainfall may persist over a large part of the U.S. for the next
several years.  Such a situation would be bad for river runners
depending on a good spring runoff, but good for flatwater paddlers on
Lake Powell.

<-David Schultz, University of Oklahoma and NOAA/National Severe
Storms Laboratory, Norman, Oklahoma>