|
This is a catalog of
nationwide average "winter" precipitation anomalies for
previous La Niña events. It also has the average for all
events, weak events, moderate events, strong and very strong events and the wide range
of the individual seasons that went into making up each of the averages.
It
cannot be stressed strongly enough that this is a climatological analysis
and not a forecasting tool. This is especially true for the averages of
different strength events which are made up of what are a very broad range
of conditions; some that are decidedly atypical.
The
Oceanic Niño Index (ONI)
is used to identify El Niño (warm) and La Niña (cool) events in the
tropical Pacific. The ONI is the running 3-month mean SST anomaly for the
Niño 3.4 region (i.e.,
5°N-5°S, 120°-170°W).
Events are defined as 5 consecutive months at or above the +0.5° anomaly
for warm (El Niño) events and at or below the -0.5° anomaly for cool (La
Niña) events. For La NIña the threshold is further broken down into Weak (with a
-0.5°
to -0.9° SST anomaly), Moderate (-1.0° to -1.4°), Strong (-1.5° to -1.9°) events. For
the purpose of this report for an event to be weak, moderate, strong or
very strong it
much have equaled or exceeded the higher threshold for at least 3 months.
*A period of November - March was chosen as "winter" for this study
because approximately 85% of the California rainfall is during that
period.
La Niña Events:
Weak: 1954-55,
1964-65,
1971-72, 1974-75, 1983-84, 1984-85, 2000-01, 2005-06, 2008-09, 2016-17,
2017-18, 2022-23
Moderate:
1955-56, 1970-71, 1995-96, 2011-12, 2020-21, 2021-22
Strong: 1973-74, 1975-76, 1988-89,
1998-99, 1999-00, 2007-08, 2010-11
La Niña (Cool
Event)
Anomalies:
Winter (November, December, January, February, March) Impacts
|
La Niña
Precipitation |
Average -
All La Niña
ONI ≤
-0.5
 |
| 1954-55 |
1955-56 |
1964-65 |
1970-71 |
1971-72 |
 |
 |
 |
 |
 |
| 1973-74 |
1974-75 |
1975-76 |
1983-84 |
1984-85 |
 |
 |
 |
 |
 |
| 1988-89 |
1995-96 |
1998-99 |
1999-00 |
2000-01 |
 |
 |
 |
 |
 |
| 2005-06 |
2007-08 |
2008-09 |
2010-11 |
2011-12 |
 |
 |
 |
 |
 |
| 2016-17 |
2017-2018 |
2020-21 |
2021-2022 |
2022-2023 |
 |
 |
 |
 |
 |
|
| |
Average - Weak La Niña
ONI=
-0.5 to -0.9
|
| 1954-55 |
1964-65 |
1971-72 |
1974-75 |
1983-84 |
|
|
|
|
|
|
| 1984-85 |
2000-01 |
2005-06 |
2008-08 |
2016-17 |
|
|
|
|
|
|
| 2017-18 |
2022-23 |
|
|
|
|
|
|
|
|
|
|
| |
Average - Moderate La Niña
ONI=
-1.0
to -1.4
|
| 1955-56 |
1970-71 |
1995-96 |
2011-12 |
2020-21 |
|
|
|
|
|
|
| 2021-22 |
|
|
|
|
|
|
|
|
|
|
|
| |
Average - Strong La Niña
ONI
≤
-1.5
|
| 1973-74 |
1975-76 |
1988-89 |
1998-99 |
1999-00 |
|
|
|
|
|
|
| 2007-08 |
2010-11 |
|
|
|
|
|
|
|
|
|
|
|
