# Wednesday, 18 August 2021
Downtown Los Angeles Finishes 2020-2021 Rain Year at 41% of Normal. Normal Amount of Rainfall in Los Angeles Is Decreasing. La Nina Expected to Reemerge.

WRCC/HPRCC Percent of Normal Precipitation, July 1, 2020 to June 30 2021 Click
WRCC/HPRCC Percent of Normal Precipitation
July 1, 2020 to June 30 2021

Downtown Los Angeles (USC) ended the 2020-21 rain year (July 1 to June 30) with 5.82 inches of rain. This is about 41% of the new normal annual precipitation total of 14.25 inches. Much of the West recorded below average precipitation for the rain year.

The amount of rainfall that is considered "normal" for Downtown Los Angeles has decreased nearly an inch in the past three decades. The normal rainfall for Los Angeles was 15.14 inches based on 1971-2000 climate data, and dropped to 14.93 inches based on data from1981-2010. Analysis of 1991-2020 data provided the new normal of 14.25 inches. Interim 2006-2020 climate data is shockingly dry, with normal rainfall in Los Angeles calculated at only 11.39 inches! For more info see U.S. Climate Normals and Normals Calculation Methodology 2020 (PDF).

La Nina conditions developed in August 2020 and transitioned to ENSO-neutral in April 2021. The Oceanic Nino Index (ONI) decreased to a minimum of -1.3 in the Oct-Nov-Dec season. The EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION issued August 12, 2021 projects a 70% chance of La Nina conditions being present during November-January.

Los Angeles rainfall during La Ninas has been variable, but skewed to the drier side. The average rain year precipitation for the 24 ERSST.v5 ONI-based Cold Episodes since 1949 is 11.84 inches. The highest amount was 20.20 inches in 2010-11 and the lowest 4.68 inches in 2017-18. In the past decade, rainfall totals for Los Angeles have been less in the second year of successive cold episodes, but this pattern doesn't hold up over the entire record.

More information about Southern California weather and climate can be found using our WEATHER LINKS page.

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Wednesday, 18 August 2021 11:00:07 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Tuesday, 17 August 2021
La Nina Comparison Chart for 2020-21.

The following chart compares various climate parameters for cold ENSO episodes that have occurred since 1949. Except where noted, the cold episodes listed are those specified in the CPC's tabulation of Cold & Warm Episodes by Season. The cold and warm episodes are based on the Oceanic Niño Index (ONI), which is calculated using the three month running mean of ERSST.v5 SST anomalies in the Niño 3.4 region with multiple-centered 30 year base periods. A description of the parameters follows the chart. With the exception of years prior to 1957, a Nov-Mar GWO phase space plot is included for each episode.

Year ERSST
Version 		Nov-Mar
AAM 		Peak MEI Peak MEI Season Peak
ONI 		Peak ONI Season L.A. Rain GWO
Phase Plot
1949-501,2 v5 -- -1.445 APRMAY -1.5 DJF 9.94 --
1950-511,3 v4 -- -1.235 NOVDEC -0.8 NDJ, DJF 8.21 --
1954-551 v5 -- -1.528 MAYJUN (54) -0.9 ASO 11.94 --
1955-561 v5 -- -2.209 MAYJUN (55) -1.7 OND 16.00 --
1956-571,3 v3b -- -1.490 MAYJUN (56) -0.6 JJA, JAS 9.54 --
1961-623 v2 -0.514 -1.065 DECJAN -0.3 ASO, SON 18.79 Click for Nov-Mar GWO Phase Space Plot
1962-633 v3b -1.260 -0.837 JANFEB -0.4 OND, NDJ 8.38 Click for Nov-Mar GWO Phase Space Plot
1964-65 v5 -1.146 -1.476 JULAUG -0.8 ASO - DJF 13.69 Click for Nov-Mar GWO Phase Space Plot
1967-683 v4 -0.770 -1.106 APRMAY -0.7 JFM 16.58 Click for Nov-Mar GWO Phase Space Plot
1970-71 v5 -0.977 -1.870 MARAPR -1.4 DJF, JFM 12.32 Click for Nov-Mar GWO Phase Space Plot
1971-72 v5 -0.173 -1.439 AUGSEP -1.0 OND 7.17 Click for Nov-Mar GWO Phase Space Plot
1973-74 v5 -1.332 -1.912 DECJAN -2.0 NDJ 14.92 Click for Nov-Mar GWO Phase Space Plot
1974-75 v5 -0.843 -1.230 OCTNOV -0.8 OND 14.35 Click for Nov-Mar GWO Phase Space Plot
1975-76 v5 -0.714 -1.968 SEPOCT -1.7 NDJ 7.22 Click for Nov-Mar GWO Phase Space Plot
1983-844 v5 -1.095 -0.7 MJ -1.0 OND 10.43 Click for Nov-Mar GWO Phase Space Plot
1984-85 v5 -0.597 -1.2 AM -1.1 NDJ 12.82 Click for Nov-Mar GWO Phase Space Plot
1988-89 v5 -1.140 -1.8 JJ, JA, AS -1.8 OND, NDJ 8.08 Click for Nov-Mar GWO Phase Space Plot
1995-96 v5 -0.227 -0.9 AS, MJ -1.0 SON - NDJ 12.46 Click for Nov-Mar GWO Phase Space Plot
1998-99 v5 -0.541 -1.7 JA -1.6 NDJ, DJF 9.09 Click for Nov-Mar GWO Phase Space Plot
1999-00 v5 -0.781 -1.4 ND, FM -1.7 NDJ, DJF 11.57 Click for Nov-Mar GWO Phase Space Plot
2000-01 v5 -0.798 -0.9 ON, JF -0.7 OND - DJF 17.94 Click for Nov-Mar GWO Phase Space Plot
2005-06 v5 -0.613 -0.8 MA -0.9 DJF 13.19 Click for Nov-Mar GWO Phase Space Plot
2007-08 v5 -1.012 -1.5 FM -1.6 NDJ, DJF 13.53 Click for Nov-Mar GWO Phase Space Plot
2008-09 v5 -0.597 -1.1 JA, AS, SO -0.8 DJF, JFM 9.08 Click for Nov-Mar GWO Phase Space Plot
2010-11 v5 -0.596 -2.4 JJ, JA -1.6 ASO-NDJ 20.20 Click for Nov-Mar GWO Phase Space Plot
2011-12 v5 -0.370 -1.4 SO -1.1 SON, OND 8.69 Click for Nov-Mar GWO Phase Space Plot
2016-17 v5 0.088 -0.6 SO, FM -0.7 SON, OND 19.00 Click for Nov-Mar GWO Phase Space Plot
2017-18 v5 -0.549 -1.3 MA -1.0 NDJ 4.68 Click for Nov-Mar GWO Phase Space Plot
2020-215 v5 -0.105 -1.2 AS, SO, ND, DJ -1.3 OND 5.82 Click for Nov-Mar GWO Phase Space Plot
1. AAM and AAM tendency anomaly data not available.
2. Based on ONI values beginning with DJF 1949-50.
3. Not a Cold Episode using ERSST v5.
4. MEI values are v2 starting with 1983-84.
5. Data as of August 16, 2021.

ERSST Version: The most recent ERSST version for which the episode was designated a cold episode. (See Peak ONI below.)

Nov-Mar AAM: The mean of the global relative atmospheric angular momentum anomaly for the period November 1 to March 31 of the following year. GWO phase space data is calculated using code from the Global Synoptic Dynamic Model page of the PSD Map Room Climate Products. Reference Weickmann and Berry, 2008.

Peak MEI:The peak seasonal value of the Multivariate ENSO Index (MEI). MEI values are v2 starting with 1983-84. MEI v1 values were last updated in March 2018.

Peak MEI Season: The peak bi-monthly season(s) for which the MEI is computed.

Peak ONI: The peak Oceanic Niño Index (ONI) based on SST anomalies in the Niño 3.4 region. Reference Climate Prediction Center Cold & Warm Episodes by Season (Multiple centered 30-year base periods.)

Peak ONI Season: The peak tri-monthly season(s) for which the ONI is computed.

L.A. Rain: The July-June rainfall year precipitation total in inches for Downtown Los Angeles (USC). Reference WRCC LOS ANGELES DWTN USC CAMPUS, CA. See Precipitation>Quantity>Monthly Precipitation Listings>Monthly Totals.

GWO Phase Space Plot: Plot of global relative atmospheric angular momentum anomaly vs. global relative atmospheric angular momentum tendency anomaly for the period November 1 to March 31 of the following year. Data is calculated using code from the Global Synoptic Dynamic Model page of the PSD Map Room Climate Products. Reference Weickmann and Berry, 2008.

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climate | Global Wind Oscillation (GWO) | La Nina | Los Angeles rainfall | Multivariate ENSO Index (MEI)
Tuesday, 17 August 2021 08:10:12 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   |