Last update: 10 April 2012
A La Niña advisory from the Climate Prediction Center (CPC) expects the La Niña conditions to return to netural by late April 2012.
Moderation of the cooler equatorial waters can be seen in an animation from the Climate Prediction Center of the weekly sea surface temperature (SST) anomalies from January 18 to April 4, 2012:
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California and Nevada
La Niña in a nutshell:
- LN conditions are cool SST anomalies in the central and eastern tropical Pacific, increased trade winds, and convective clouds shifted to the far western tropical Pacific.
- Seasonal forecasts and previous strong LN events indicate that LN conditions will moderate in northern hemisphere spring 2012.
- Previous LNs have quite strongly tended to produce dry or at most moderate precipitation in southern California (south of Pt. Conception) and extreme southern Nevada (while 2010/2011 was quite the opposite with a wet winter for much of California and Nevada, 2011/2012 has followed the typical dry pattern).
- Historically winter temperature in California has tended to be somewhat cooler than normal, especially along the coastal margin, while Nevada temperatures have fallen into the near-normal range.
Global sea surface temperature anomalies for the week of April 1 to 7, 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 the moderating La Niña conditions to transition to El Niño (warm) conditions during winter/spring of 2012/2013. 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:
La Niña and its impacts on California and Nevada
Klaus Wolter (NOAA CIRES Climate Diagnostics Center, 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. Blue indicates times of La Niña events. Click here to see the MEI web page that Klaus has put together (note this web page has many La Niña related links).
In order to compare the current La Niña with previous events, Klaus had made a figure showing the MEI for 7 of the strongest events since 1949, with the current event in black (see black dashed '10+' line).
While a La Niña doesn't gaurantee a dry 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 below normal during an La Niña:
The Climate Prediction Center provides seasonal probability maps for temperature and precipitation during La Niña episodes. The maps below show the conditional probabilities that mean temperatures or total precipitation will rank among the highest and lowest one-third of the 45-year climatological record (terciles), given a moderate-to-strong La Niña episode. The maps are trend-adjusted so they assume the continuation of long-term trends through the period. The probability for the class the distribution is skewed towards is color-coded. For example, when the highest probability in a given region is for the warmest (wettest) class, this probability is denoted by yellow and red (green) shades; when the highest probability is for the coldest (driest) class, it is indicated by blue (brown and orange) shades; etc. For each shaded climate region on each chart, the probability for the opposite tercile class (for example, the likelihood for the cold tercile in regions shaded red) is rounded to the nearest 10% and plotted as a value in the region.
December-February January-March February-April Precipitation December-February January-March February-April Temperature