Effect of the
1997-98 El Niño on Individual Large-Scale Weather Events.
"Effect of the 1997-98 El Niño on Individual Large-Scale Weather Events."
Barsugli J. J., J. S. Whitaker, A. F. Loughe, P. D. Sardeshmukh and Z. Toth
Bull. Amer. Met. Soc., July 1999
ABSTRACT
Can an individual weather event be attributed to El Niño? This question is
addressed quantitatively using ensembles of medium-range weather forecasts
made with and without tropical sea surface temperature anomalies. The National
Centers for Environmental Prediction (NCEP) operational medium-range forecast
model is used. It is found that anomalous tropical forcing affects forecast
skill in midlatitudes as early as the fifth day of the forecast. The effect of
the anomalous sea surface temperatures in the medium range is defined as the
synoptic El Niño signal. The synoptic El Niño signal over North America is
found to vary from case-to-case, and sometimes can depart dramatically from
the pattern classically associated with El Niño. This method of parallel
ensembles of medium-range forecasts provides information about the changing
impacts of El Niño on time scales of a week or two that is not available from
conventional seasonal forecasts.
Knowledge of the synoptic El Niño signal can be used to attribute aspects of
individual weather events to El Niño. Three large-scale weather events are
discussed in detail: the January 1998 ice storm in the northeastern United
States and southeastern Canada, the February 1998 rains in central and
southern California, and the October 1997 blizzard in Colorado. Substantial
impacts of El Niño are demonstrated in the first two cases. The third case is
inconclusive.
Please contact Joe Barsugli (joseph.barsugli@colorado.edu) for further information.
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