HIGHLIGHT: Normals have been changed to 1981-2010 as of last month, note substantial changes in the weights!!!. The Nino34 climos have gone up by about 0.1K

The seasonal mean NINO3.4 anomaly was -0.74 for MAM2011, down from FMA. La Nina has weakened further, not unusual for the season of course.

The CA method, acting on global MAM2011 seasonal means as latest input, has 100% of its members in La Nina territory only thru AMJ. La Nina conditions, but weaker and only in a few members, are expected by CA for rest of 2011, with a slight increase in coolness towards the end of the year. Thus there could a weak La Nina next winter. Some members crawl into positive territory by early spring 2012. Spread is high and peculiar with some members that go warmest first and end coldest (and vice versa).

Weights have changed because a) three months ago the matrix size has increased by one, from 53 to 54, and this resets the weights given co-linearity among years, and b) we have changed normals as of the May issued forecast to the 1981-2010 base period. There are six years with high +ve weight!, and seven high -ve weight. OCN flavor is much reduced, with more +ve weight given to older years than ever before. Also note the string of negative weights for 1985 to 1995, a strong sign of interdecadal variation.

Table 1. Inner products (IP; scaled such that the sum of absolute values is 100; not shown) and weights (Wgt multiplied by 100.) of each of the years to construct an analogue to the sequence of 12 consecutive overlapping 3-month periods defined as the base (currently the 12 overlapping seasons string AMJ2010 thru MAM2011). Years in the table are labeled by the year of the middle month of the most recent predictor season. Weights for 1956 and 2010 are less (by 50%) because only half the members use these years ("early" members use 1956, "late" members 2010). Data currently thru May 2011.

Year	IP	Wgt	Year	IP	Wgt	Year	IP	Wgt	Year	IP	Wgt	Year	IP	Wgt	Year	IP	Weigt
1956	xx	1	1966	xx	-10	1976	xx	6	1986	xx	-9	1996	xx	18	2006	xx	2
1957	xx	-2	1967	xx	0	1977	xx	-9	1987	xx	-8	1997	xx	7	2007	xx	-1
1958	xx	-9	1968	xx	-10	1978	xx	5	1988	xx	-7	1998	xx	-4	2008	xx	17
1959	xx	-7	1969	xx	9	1979	xx	1	1989	xx	2	1999	xx	4	2009	xx	5
1960	xx	-19	1970	xx	8	1980	xx	1	1990	xx	-5	2000	xx	9	2010	xx	10
1961	xx	-1	1971	xx	8	1981	xx	6	1991	xx	-2	2001	xx	-11	2011	xx	NA
1962	xx	11	1972	xx	5	1982	xx	1	1992	xx	-10	2002	xx	7		xx	Xx
1963	xx	17	1973	xx	-3	1983	xx	0	1993	xx	-11	2003	xx	-7		xx	Xx
1964	xx	-8	1974	xx	19	1984	xx	1	1994	xx	-10	2004	xx	-5		xx	Xx
1965	xx	-8	1975	xx	1	1985	xx	-9	1995	xx	-4	2005	xx	0		xx	Xx

Weights are high +ve (>+0.10) for 2010,2008,1996,1974,1963,1962. Weights are high -ve (< - 0.10) for 2001,1994,1993,1992,1968,1966,1960.

Ens ave Nino34 anomaly forecasts, for leads -3, -2, -1, 0 etc: in plain numbers (ensemble mean):

-0.74	-0.69	-0.51	-0.23	-0.16	-0.15	-0.19	-0.27	-0.31	-0.36	-0.35	-0.34	-0.32	-0.32	-0.25	-0.18	-0.07	-0.02	0.01	0.01	0.03
MAM		MJJ11		JAS		SON		NDJ		JFM12		MAM		MJJ		JAS		SON12		NDJ

One month ago:

-1.02	-0.97	-0.74	-0.45	-0.33	-0.25	-0.26	-0.33	-0.45	-0.48	-0.47	-0.4	-0.34	-0.26	-0.25	-0.18	-0.13	-0.01	0.06	0.11	0.12
	MAM11		MJJ		JAS		SON		NDJ		JFM		MAM12		MJJ		JAS		SON

Two months ago:

-1.26	-1.23	-1.01	-0.64	-0.49	-0.41	-0.36	-0.38	-0.43	-0.54	-0.54	-0.49	-0.36	-0.18	-0.06	-0.02	0.03	0.06	0.18	0.25	0.32
JFM11		MAM			MJJ		JAS		SON11		NDJ		JFM12		MAM		MJJ		JAS

Three months ago:

-1.46	-1.49	-1.33	-0.99	-0.78	-0.69	-0.67	-0.65	-0.66	-0.71	-0.79	-0.77	-0.67	-0.47	-0.27	-0.05	0.03	0.09	0.08	0.15	0.2
	JFM11		MAM		MJJ		JAS		SON11		NDJ		JFM12		MAM		MJJ		JAS12

Four months ago:

-1.54	-1.62	-1.66	-1.39	-1.07	-0.83	-0.67	-0.6	-0.57	-0.59	-0.62	-0.69	-0.68	-0.5	-0.36	-0.21	-0.02	0.08	0.17	0.2	0.27
NDJ		JFM		MAM11		MJJ		JAS		SON		NDJ		JFM12		MAM		MJJ		JAS

Anomalies relative to 1981-2010 climo, as of this release. Older forecasts (1-4 months ago) are relative to 71-2000