Climate Fact: ENSO and Regional Rainfall (South)
Winter storm season is here. Storms will be blowing in from the Pacific, bringing rainfall to lower elevations and snow to the mountains. This year, the eastern tropical Pacific is in an El Niño phase, meaning that its waters are warmer than average. When the eastern Pacific is in an El Niño phase, the southern U.S. can expect:
a) more than normal rainfall and cooler temperatures
b) less than normal rainfall and warmer temperatures
c) about normal rainfall and about normal temperatures
The correct answer is a. The South gets more than normal rainfall during El Niño years and less than normal rainfall during La Niña years when the colder waters in the eastern Pacific cause the Pacific storm track to shift north and miss us. During El Niño, not only does the storm track head right for us, it is even stronger than it is during the La Niña phase. Another effect of El Niño is cooler than normal winters in the South from about Texas eastward.
View a schematic diagram of how El Niño and La Niña events affect wintertime rainfall and temperature: http://www.earthgauge.net/climate-facts-image-library#5. For more information on El Niño, including seasonal forecasts by region, visit: http://www.elnino.noaa.gov/. Learn more about what Northern Hemisphere storm tracks are and how they work: http://www.earthgauge.net/wp-content/CF_Storm%20Tracks.pdf.
Seasons: Winter
Sources: Eichler, T and Higgins W. “Climatology and ENSO-Related Variability of North American Extratropical Cyclone Activity.” Journal of Climate 19 (2006): 2076-2093 and National Oceanic and Atmospheric Administration: Climate Prediction Center. Accessed Online 7 December 2009 (http://www.cpc.ncep.noaa.gov/products/precip/CWlink/stormtracks/eisdiffobs.meta.gif