ABSTRACT

Barsugli, J. J, J. S. Whitaker, A. F. Loughe, P. D. Sardeshmukh and Z. Toth, 1998: Effect of the 1997-98 El Niño on Individual Large-Scale Weather Events. Bull. Amer. Met. Soc. 80, 1399-142.

^(PDF)

^{Effect of the 1997-98 El Niño on Individual Large-Scale
Weather Events.}

^{Joseph J. Barsugli, Jeffrey S. Whitaker,
Andrew F. Loughe and Prashant Sardeshmukh}

^{NOAA-CIRES Climate Diagnostics Center, Boulder,
CO}

^{Zoltan Toth}

^{NOAA/NCEP/EMC, Washington D.C.}

^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
operational medium-range forecast model is used. It is found that anomalous
tropical forcing substantially 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 midlatitude 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 few days
to a two weeks 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.}