Last update: 7 November 2012
An El Niño watch from the Climate Prediction Center (CPC) discusses borderline ENSO-neutral/ weak El Niño conditions that are expected to continue into Northern Hemisphere winter 2012-13, possibly strengthening during the next few months.
Areas of warmer waters can be seen sporadically over the tropical Pacific. The latest images show an increase in warmer waters over the western tropical Pacific and over the South Pacific Convergence Zone.
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California and Nevada
El Niño in a nutshell:
- EN conditions are warm SST anomalies in the central and eastern tropical Pacific, decreased trade winds, and convective clouds shifted to a broad region of the central tropical Pacific.
- Seasonal forecasts are showing weak EN conditions through the winter of 2012/2013.
- Previous ENs have quite strongly tended to produce above normal precipitation in California and southern Nevada, especially along the coastal regions where precipitation may be 5 inches or more above normal.
- Historically winter temperature in southern California and Nevada has tended to be somewhat cooler than normal, while temperatures over the rest of the region have fallen into the near-normal range.
Global sea surface temperature anomalies for the week of October 28 to November 3, 2012, are shown below. This image is from the Earth System Research Laboratory.
SST anomalies for specific regions of the tropical Pacific (Niño regions; shown to the left below) for 1991 to present (shown to the right below) compare the strength of various La Niña episodes (blue) and El Niño episodes (orange).
The current forecast from the Experimental Climate Prediction Center at the Scripps Institution of Oceanography is forecasting warm El Niño conditions for late 2012 into early 2013. Below is the forecast sea surface temperature anomaly for the tropical Pacific covering the months of December 2012 through February 2013.
Find more forecast images and information about this forecast on the Experimental El Niño Forecast web page:http://meteora.ucsd.edu/~pierce/elnino/elnino.html
Other forecasts can be found at:
El Niño and its impacts on California and Nevada
Klaus Wolter (NOAA Earth System Research Laboratory, Boulder CO) has developed a Multivariate ENSO Index (MEI) based on six observed variables over the tropical Pacific: sea-level pressure, zonal wind, meridional wind, sea surface temperature, surface air temperature and total cloudiness. The time series of this index from 1950 to now is shown below. Red indicates times of El Niño events. Click here to see the MEI web page that Klaus has put together (note this web page has many El Niño related links).
The progression of MEI during 7 of the strongest El Niño events is shown below to the left. The progression of MEI during 4 weak El Niño events (plus the current event) is shown below to the right.
While an El Niño doesn't gaurantee a wet winter in California, the graphs below for San Diego (left) and an 8-station California index (8 stations in Northern Sierra used by the California Department of Water Resources, right), show that more often than not, precipitation is above normal during an El Niño:
The maps below show the composite precipitation (left) and temperature (right) anomalies over the US Climate Divisions during strong El Niño years: 1957/58, 1965/66, 1972/73, 1982/82, 1991/92, 1998/99 and 2009/10. The loops rotate through 3-month periods starting with October-December and ending with March-May. Red/blue areas show when precipitation is below/above normal during these strong El Niño years (left). Red/blue areas show when temperature is above/below normal during these years.