Overview:  El Niño events have are defined from the Oceanic Niño Index (ONI) into Weak, Moderate, Strong and Very Strong events.   Then the seasonal (July 1 through June 30) percent of normal precipitation for each category, plus a collective category of "all" warm events, was collated for a number of cities and geographic areas. These include three major watersheds, the Northern Sierra Nevada Eight Station Index (8SI, map), the Southern Sierra Nevada Five Station Index (5SI, map) and the Tulare Basin Six Station Index (6SI, map). Additionally the seven NCDC climate division (see map) and the entire state of California (CA) averages were compared to the ENSO events.  These comparisons was done in terms of both average seasonal precipitation and also the number of occurrences within percent of normal categories.

Observations:  The best "signal" associated with warm ENSO (El Niño) events is, as would be expected, with the "Very Strong" events all at least 140% of normal except for Climate Divison 3 which was between 120% and 140%.  In the "Strong"category Southern California showed a significant positive signature with the three seasons categorized as strong, all  averaged above normal precipitation with the highest percentages of normal (PON) in Los Angeles, Climate Divisions 6 and 7.  During weak and moderate warm events there is no such signal with the number of years of above and below normal being fairly evenly split statewide.

Important Caveat:  The data presented here is a climatology of past events and is made up of a broad range of events from a small sample that are averaged together.  Consequently, like all averages, this type of data should not be used as a forecast! 

El Niño

Table 1.  All El Niño Events - Average Percent of Normal Precipitation (23 events)

ENSO Type	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7	CA	8SI	5SI	6SI	SF	EKA	SAC	FAT	LAX
All El Niño	108%	106%	105%	114%	111%	127%	124%	111%	103%	105%	111%	102%	100%	103%	110%	126%
Weak El Niño	107%	107%	111%	110%	112%	126%	122%	111%	105%	109%	112%	95%	99%	99%	109%	126%
Moderate El Niño	87%	81%	78%	86%	83%	99%	109%	87%	79%	77%	83%	78%	90%	79%	83%	91%
Strong El Niño	115%	110%	105%	131%	116%	133%	120%	116%	102%	100%	112%	123%	96%	116%	113%	140%
Very Strong El Niño	162%	167%	150%	198%	182%	212%	190%	174%	162%	174%	191%	181%	146%	183%	190%	209%

Table 2.  All El Niño - Years by Percent of Normal Categories (23 events)

% of Normal	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7	CA	8SI	5SI	6SI	SF	EKA	SAC	FAT	LAX
<80%	7	8	8	7	7	7	5	5	8	9	8	8	3	9	8	6
80-100%	2	2	4	4	5	1	4	5	2	4	3	3	9	3	4	3
100-120%	5	5	3	2	1	4	4	4	6	1	2	5	6	2	2	2
120-140%	5	4	5	2	3	2	1	3	4	4	3	2	3	5	3	1
>140%	4	4	3	8	7	9	9	6	3	5	7	5	2	4	6	11

Table 3.  Weak El Niño - Years by Percent of Normal Categories (12 events)

% of Normal	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7	CA	8SI	5SI	6SI	SF	EKA	SAC	FAT	LAX
<80%	3	3	4	3	3	5	5	3	3	4	3	4	1	4	5	4
80-100%	0	1	1	3	3	1	1	2	1	2	3	2	5	2	1	2
100-120%	4	3	2	0	0	0	0	1	4	0	0	3	5	1	1	0
120-140%	4	4	3	2	2	0	0	3	3	3	2	2	1	4	2	0
>140%	1	1	2	4	4	6	6	3	1	3	4	1	0	1	3	6

Table 4.  Moderate El Niño - Years by Percent of Normal Categories (6 events)

% of Normal	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7	CA	8SI	5SI	6SI	SF	EKA	SAC	FAT	LAX
<80%	4	4	3	3	3	2	0	2	4	4	4	3	2	4	2	2
80-100%	0	1	3	1	2	0	3	2	0	1	0	1	2	1	3	1
100-120%	1	1	0	2	1	3	2	2	2	1	2	2	1	1	1	2
120-140%	1	0	0	0	0	1	0	0	0	0	0	0	1	0	0	0
>140%	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	1

Table 5.  Strong El Niño - Years by Percent of Normal Categories (3 events)

% of Normal	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7	CA	8SI	5SI	6SI	SF	EKA	SAC	FAT	LAX
<80%	0	1	1	1	1	0	0	0	1	1	1	1	0	1	1	0
80-100%	2	0	0	0	0	0	0	1	1	1	0	0	2	0	0	0
100-120%	0	1	1	0	0	1	2	1	0	0	0	0	0	0	0	0
120-140%	0	0	1	0	1	1	1	0	1	1	1	0	1	1	1	1
>140%	1	1	0	2	1	1	0	1	0	0	1	2	0	1	1	2

Table 6.  Very Strong El Niño - Years by Percent of Normal Categories (2 events)

% of Normal	Div. 1	Div. 2	Div. 3	Div. 4	Div. 5	Div. 6	Div. 7	CA	8SI	5SI	6SI	SF	EKA	SAC	FAT	LAX
<80%	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
80-100%	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
100-120%	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
120-140%	0	0	1	0	0	0	0	0	0	0	0	0	0	0	0	0
>140%	2	2	1	2	2	2	2	2	2	2	2	2	2	2	2	2

Table 7. Percent of Normal (1981-2010) Rainfall for All El Nino Years
				1	2	3	4	5	6	7	CA	8SI	5SI	6SI	SF	EKA	SAC	FAT	LAX
			Normal	49.77"	36.69"	20.46"	22.03"	20.70"	17.80"	6.35"	24.10"	53.90"	41.76"	30.01"	23.65"	40.33"	18.52"	11.50"	14.93"
ENSO Type
Weak	1951	-	1952	123%	129%	133%	135%	135%	162%	147%	134%	132%	123%	148%	138%	118%	129%	121%	176%
Weak	1952	-	1953	118%	102%	98%	80%	82%	75%	75%	96%	100%	75%	88%	89%	118%	88%	84%	63%
Weak	1953	-	1954	107%	89%	78%	78%	82%	91%	77%	89%	92%	81%	86%	60%	105%	73%	77%	80%
Strong	1957	-	1958	153%	142%	128%	161%	143%	160%	126%	147%	134%	124%	137%	154%	121%	155%	165%	142%
Weak	1958	-	1959	77%	68%	73%	61%	59%	53%	59%	67%	71%	61%	48%	44%	81%	59%	60%	37%
Moderate	1963	-	1964	78%	68%	85%	62%	71%	71%	79%	73%	67%	71%	70%	52%	93%	67%	59%	53%
Strong	1965	-	1966	88%	71%	79%	75%	73%	97%	109%	81%	71%	75%	63%	69%	80%	57%	53%	137%
Weak	1968	-	1969	120%	128%	147%	161%	169%	175%	142%	145%	127%	163%	186%	106%	118%	130%	200%	184%
Weak	1969	-	1970	111%	113%	115%	80%	86%	63%	69%	97%	111%	97%	79%	88%	95%	93%	79%	52%
Strong	1972	-	1973	95%	110%	104%	144%	122%	129%	113%	114%	96%	95%	128%	145%	86%	136%	121%	142%
Weak	1976	-	1977	41%	41%	68%	50%	50%	66%	84%	52%	37%	45%	54%	47%	44%	38%	66%	82%
Weak	1977	-	1978	127%	131%	124%	157%	157%	207%	200%	147%	132%	148%	155%	114%	90%	142%	158%	224%
Weak	1979	-	1980	110%	118%	133%	121%	128%	165%	180%	128%	111%	134%	136%	104%	94%	128%	104%	181%
Very Strong	1982	-	1983	162%	166%	164%	193%	186%	199%	191%	176%	166%	187%	194%	161%	147%	192%	205%	209%
Moderate	1986	-	1987	72%	62%	67%	60%	63%	61%	82%	65%	61%	56%	61%	59%	69%	56%	81%	51%
Moderate	1987	-	1988	77%	73%	64%	73%	73%	99%	115%	77%	65%	63%	73%	75%	80%	75%	70%	84%
Moderate	1991	-	1992	68%	71%	63%	92%	78%	124%	155%	82%	67%	64%	65%	81%	54%	71%	96%	141%
Weak	1994	-	1995	143%	163%	166%	161%	164%	182%	149%	161%	159%	169%	153%	144%	128%	127%	165%	163%
Very Strong	1997	-	1998	154%	160%	132%	191%	168%	211%	177%	167%	154%	154%	179%	200%	145%	174%	175%	208%
Moderate	2002	-	2003	117%	105%	91%	99%	94%	105%	90%	103%	108%	91%	104%	101%	132%	90%	85%	110%
Weak	2004	-	2005	101%	110%	115%	144%	139%	192%	206%	130%	107%	129%	127%	135%	110%	118%	138%	249%
Weak	2006	-	2007	75%	62%	56%	50%	53%	31%	32%	57%	67%	59%	56%	71%	88%	59%	52%	22%
Moderate	2009	-	2010	99%	97%	93%	115%	105%	114%	113%	103%	99%	107%	113%	102%	110%	112%	107%	110%

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