The Department of Water Resources convened researchers from the
University of Colorado, the California-Nevada Applications Program RISA
Center at the Scripps Institution of Oceanography, and the National
Oceanic and Atmospheric Administration’s (NOAA’s) Hydrometeorology
Testbed program to develop and review an experimental forecast for this
winter’s water supply outlook.
A primary source of skill in making seasonal climate outlooks for the
Western U.S. is the status and expected behavior of the El Niño-
Southern Oscillation (ENSO). ENSO neutral conditions were diagnosed
in the tropical Pacific Ocean in late 2012, and will probably continue into
early 2013. Given ENSO neutral conditions, an experimental statistical
forecast combined with consideration of a negative Pacific Decadal
Oscillation (PDO), positive Atlantic Multidecadal Oscillation, average of
North Atlantic Oscillation conditions, Alaskan temperatures, and Indian
Ocean Dipole status suggests the following outlook:
�� Drier than normal for the northern two-thirds of California and in
southeastern California through April
�� Near-normal or possibly wetter than average for the central and south
coastal regions
�� Drier than normal for the Colorado River Basin, an important source of
water supply for Southern California
“The expected negative PDO appears to carry the most weight as a
forcing factor this winter”, according to Klaus Wolter of the University of
Colorado, who was the chief architect of the experimental outlook. Other
factors such as the Madden-Julian Oscillation (MJO) may also be
influential, although the MJO acts at shorter time scales than seasonally
persistent patterns such as ENSO. This winter’s expected MJO
conditions do not favor enhancement of atmospheric river (AR) storms,
which are often important to both water supply and flood conditions in
the state. “Our Hydrometeorology Testbed work has provided
preliminary evidence that AR storms making landfall in California are
most active in certain phases of the MJO”, said Marty Ralph of NOAA.