Last update: 5 October 2015
El Niño Advisory: El Niño/Southern Oscillation (ENSO) diagnostic discussion issued by the Climate Prediction Center (NCEP): 10 September 2015
An El Niño advisory from the Climate Prediction Center (CPC) discusses the current El Niño (EN) conditions that are expected to continue through Northern Hemisphere winter 2015-16, gradually weakening through spring 2016.
Areas of very warm waters can be seen 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.
California and Nevada
El Niño in a nutshell:
- EN conditions are warm sea surface temperature anomalies (SSTA) 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 strong EN conditions through the winter of 2015-16 (a strong EN exhibits SSTA above +1.5oC over a region of the central Pacific called the Niño3.4 region).
- The warm SSTA in the tropical Pacific alters large-scale atmospheric circulation patterns which can lead to higher or lower precipitation for some regions.
- 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 weekly sea surface temperature anomalies 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 SSTA from David Pierce at the Scripps Institution of Oceanography is forecasting strong El Niño conditions in the winter of 2015-16. Below is the forecast sea surface temperature anomaly for the tropical Pacific covering the months of December 2015 through February 2016.
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. Current conditions show the current El Niño event is the second strongest during the period of record.
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, 1982/83, 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.