Golden Gate Weather Services - Winter 2000 Outlook

Precipitation & Temperature Climatology for a Non-Niño Season following La Niña

The current precipitation season (July 2000 through June 2001) presents a relatively unique climatological occurrence. It is only the sixth time in the past 50 years when a Non-Niño (i.e., neither El Niño or La Niña) follows a La Niña season. From NOAA Climate Prediction Center analyses of the ENSO (El Niño-Southern Oscillation) events since 1950, the other seasons in which this has occurred are 1956-57, 1971-72, 1985-86, 1989-90 and 1996-97.

The only one of these five cases (1956-57) which involved a two year La Niña, like was just experienced in the two year period 1998-2000.

The composite for the five precipitation seasons in questions shows no clear wet or dry bias for California. For the United States in general the only significant wet bias is in Oklahoma, Arkansas and northeast Texas and the Cascades of Washington.

Likewise the composite of temperature for these five seasons only shows a very slight warm bias for California, except in the deserts of California which edge up to a positive 1.1 degree F anomaly. Nationwide the signature is similarly unimpressive with no widespread strong biases.

For the individual seasons in California there was a split with two seasons having a positive precipitation anomaly (1985-86 and 1996-97) and three being on the dry side (1956-57, 1971-72 and 1989-90). Nationwide the signal appears just as muddled with no significant positive or negative bias.

Also of interest is the fact that all of this non-Niño seasons that followed a La Niña were followed by an El Niño. A look at the SST forecasts for this coming summer from both the NWS and Scripps shows at least a slightly positive SST anomaly developing during the summer of early Fall.

Composite Precipitation Anomaly (1956-57, 1971-72, 1985-86, 1989-90, 1996-97)

The following graphics show the precipitation anomaly, by climate division, for a composite of these 5 seasons. (click images to enlarge)

Composite Temperature Anomaly (1956-57, 1971-72, 1985-86, 1989-90, 1996-97)

The following graphics show the temperature anomaly, by climate division, for a composite of these 5 seasons. (click images to enlarge)

NWS Winter Precipitation Outlook The above ambiguity from the climatological data is reflected in the 90 days winter forecasts from the National Weather Service Climate Prediction Center. The December through February shows a moderately positive anomaly in eastern Texas, Louisiana while there is NO SIGNAL for the March through May period.	Dec. 2000-Feb. 2001	Mar. 2001-May. 2001
NWS Winter Temperature Outlook The temperature anomaly for December through February shows a moderate positive signal in the southern Great Basin which expands over much of the Great Basin and Pacific Coast states in the March through May time frame.	Dec. 2000-Feb. 2001	Mar. 2001-May. 2001