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# Tuesday, 17 August 2021

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.

Tuesday, 17 August 2021 08:10:12 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Thursday, 09 July 2020
Downtown Los Angeles (USC)
November 2019-April 2020 Rain
Month Precip
in.
Normal
in.
Percent of Normal 500mb
Height
Anomaly
November 2.12 1.04 204%
December 4.84 2.33 208%
January 0.32 3.12 10%
February 0.04 3.80 1%
March 4.35 2.43 179%
April 3.02 0.91 332%
Rain Year 14.86 14.93 99.5%  

To say Los Angeles recorded a normal amount of rainfall during a rain year is not the same as saying the rain year was typical. As I scan down the monthly precipitation totals in Los Angeles' 143 year weather record, it seems the pattern of rainfall is different for every one.

Our most recent rain year, 2019-2020, is an excellent example. Wet weather in November and December was followed by equally dry weather in January and February. Just when it looked like the rain season was done, wet weather returned in March and April. The end product was a "normal" rain year, with 14.86 inches of precipitation recorded at Downtown Los Angeles (USC) from July 1, 2019 to June 30, 2020..

As can be seen from the mean monthly 500mb height anomalies, much of this rain season's precipitation resulted from a semi-persistent pattern of upper-level low pressure off the coast of Southern California. The pattern of precipitation in the West for the rain year reflects the position of these lows.

Based on the CPC's Oceanic Nino Index (ONI), equatorial Pacific SSTs marginally capable of supporting El Nino conditions developed in the Oct-Nov-Dec 2019 season, but ocean-atmosphere coupling characteristic of El Nino did not follow.

There is some evidence that suggests Southern California precipitation is more closely correlated with AAM than with Nino 3.4 SST. Here is an extended GWO phase space plot for November 2019 - May 2020. The November-March GWO Phase Plots for ONI-based warm episodes can be found on our El Nino Comparison Chart for 2019-2020 page.

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

Thursday, 09 July 2020 15:55:10 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Saturday, 04 April 2020

The following chart compares various climate parameters for warm ENSO episodes that have occurred since 1950. The warm episodes are based on the revised 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. Unless noted the warm episodes are those specified in the CPC's tabulation of Cold & Warm Episodes by Season. 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 warm episode.

Year Jul-Sep
AAM
Nov-Mar
AAM
Peak MEI Peak MEI Season Peak
ONI
Peak ONI Season L.A. Rain GWO
Phase Plot
1951-521 -- -- 0.82 JULAUG 1.2 SON 26.21 --
1952-532 -- -- 0.76 APRMAY 0.8 AMJ-MJJ 9.46 --
1953-542 -- -- 0.48 AUGSEP 0.8 SON-DJF 11.99 --
1957-583,4 -- 0.78 1.47 DECJAN, JANFEB 1.8 DJF 21.13 Click for Nov-Mar GWO Phase Space Plot
1958-594 -0.92 -0.21 0.81 JANFEB 0.6 NDJ, DJF, JFM 5.58 Click for Nov-Mar GWO Phase Space Plot
1963-64 0.01 0.05 0.88 OCTNOV, DECJAN 1.4 OND 7.93 Click for Nov-Mar GWO Phase Space Plot
1965-66 -0.83 -0.75 1.43 JULAUG 2.0 SON, OND 20.44 Click for Nov-Mar GWO Phase Space Plot
1968-69 0.13 0.51 0.85 JANFEB 1.1 DJF, JFM 27.47 Click for Nov-Mar GWO Phase Space Plot
1969-70 0.36 0.41 0.66 OCTNOV 0.9 SON 7.77 Click for Nov-Mar GWO Phase Space Plot
1972-73 -0.10 -0.24 1.83 JUNJUL, JULAUG 2.1 OND, NDJ 21.26 Click for Nov-Mar GWO Phase Space Plot
1976-77 0.29 -0.83 1.02 AUGSEP 0.9 OND 12.31 Click for Nov-Mar GWO Phase Space Plot
1977-78 -0.65 1.01 0.97 SEPOCT, OCTNOV 0.8 OND, NDJ 33.44 Click for Nov-Mar GWO Phase Space Plot
1979-80 0.49 -0.01 0.7, 0.6 ND, MA-JJ 0.6 NDJ, DJF 26.98 Click for Nov-Mar GWO Phase Space Plot
1982-83 0.94 2.34 2.9 AM 2.2 OND,NDJ, DJF 31.25 Click for Nov-Mar GWO Phase Space Plot
1986-875 0.23 0.02 2.0 MJ87 1.2 NDJ,-JFM 7.66 Click for Nov-Mar GWO Phase Space Plot
1987-885 1.16 1.00 2.0 MJ87 1.7 JAS 12.48 Click for Nov-Mar GWO Phase Space Plot
1991-92 -0.01 0.81 2.0 MA92 1.7 DJF 21.00 Click for Nov-Mar GWO Phase Space Plot
1994-95 -0.42 0.77 1.5 SO 1.1 NDJ 24.35 Click for Nov-Mar GWO Phase Space Plot
1997-98 1.82 1.49 2.3, 2.6 MJ97, MA98 2.4 OND, NDJ 31.01 Click for Nov-Mar GWO Phase Space Plot
2002-03 0.05 0.32 1.0, 0.9 JA, ND 1.3 OND 16.49 Click for Nov-Mar GWO Phase Space Plot
2004-05 -0.02 0.75 0.7, 0.8 JA04, FM05 0.7 ASO-NDJ 37.25 Click for Nov-Mar GWO Phase Space Plot
2006-07 0.14 -0.32 0.9 ON 0.9 OND-NDJ 3.21 Click for Nov-Mar GWO Phase Space Plot
2009-10 -0.10 0.30 1.1, 1.3 ON, JF-FM 1.6 NDJ 16.36 Click for Nov-Mar GWO Phase Space Plot
2014-156 -0.52 -0.29 2.2 AS15 1.2 MJJ 8.52 Click for Nov-Mar GWO Phase Space Plot
2015-166 1.34 1.64  2.2 AS15 2.6 NDJ 9.36 Click for Nov-Mar GWO Phase Space Plot
2018-19 -0.43 1.22 0.5, 0.8 AS18, FM19 0.9 OND 18.82 Click for Nov-Mar GWO Phase Space Plot
2019-207.8 -1.12 0.44 0.5 ON 0.6 JFM 14.86 Click for Nov-Mar GWO Phase Space Plot

1. AAM and AAM tendency anomaly data for 1951-52 not available.
2. Continuous warm episode from JFM 1953 to JFM 1954.
3. AAM anomaly is average for Jan-Mar 1958.
4. Continuous warm episode from MAM 1957 to JJA 1958 & OND 1958 to FMA 1959.
5. Continuous warm episode from ASO 1986 to JFM 1988.
6. Continuous warm episode from OND 2014 to AMJ 2016.
7. Marginally qualifies as ONI-based Warm Episode.
8. Data as of July 6, 2020.

Jul-Sep AAM & Nov-Mar AAM: The mean of the global relative atmospheric angular momentum anomaly for the periods July 1 to September 30 amd 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 1979-80. MEI v1 values were last updated December 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.

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.

Saturday, 04 April 2020 14:55:23 (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Friday, 05 July 2019

WRCC/HPRCC Percent of Normal Precipitation, July 1, 2018 to June 30 2019 Click
WRCC/HPRCC Percent of Normal Precipitation
July 1, 2018 to June 30 2019

Downtown Los Angeles (USC) ended the 2018-19 rain year (July 1 to June 30) with 18.82 inches of rain. This is about 126% of the normal yearly precipitation total of 14.93 inches. Much of the southwest recorded average to above average precipitation, thanks to a generally progressive pattern in the West and a strong Pacific jet this Winter.

Based on the CPC's Oceanic Nino Index (ONI), equatorial Pacific SSTs capable of supporting El Nino conditions developed in the Sep-Oct-Nov 2108 season, but ocean-atmosphere coupling characteristic of El Nino did not develop until January 2019.

Although this year's El Nino was weak and somewhat atypical, it should be noted that the Global Wind Oscillation orbited through positive AAM phases from mid October until just recently. Historically, continually positive AAM anomaly values during the Nov-Mar period have occurred during strong El Ninos, such as in 1997-98 and 1982-83. The Nov-Dec GWO Phase Plots for ONI-based warm episodes can be found on our El Nino Comparison Chart for 2018-2019 page.

There is some evidence that suggests Southern California precipitation is more closely correlated with AAM than with Nino 3.4 SST.

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

Friday, 05 July 2019 09:33:29 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Monday, 15 April 2019

The following chart compares various climate parameters for warm ENSO episodes that have occurred since 1950. The warm episodes are based on the revised 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. Unless noted the warm episodes are those specified in the CPC's tabulation of Cold & Warm Episodes by Season. 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 warm episode.

Year Jul-Sep
AAM
Nov-Mar
AAM
Peak MEI Peak MEI Season Peak
ONI
Peak ONI Season L.A. Rain GWO
Phase Plot
1951-521 -- -- 0.82 JULAUG 1.2 SON 26.21 --
1952-532 -- -- 0.76 APRMAY 0.8 AMJ-MJJ 9.46 --
1953-542 -- -- 0.48 AUGSEP 0.8 SON-DJF 11.99 --
1957-583,4 -- 0.78 1.47 DECJAN, JANFEB 1.8 DJF 21.13 Click for Nov-Mar GWO Phase Space Plot
1958-594 -0.92 -0.21 0.81 JANFEB 0.6 NDJ, DJF, JFM 5.58 Click for Nov-Mar GWO Phase Space Plot
1963-64 0.01 0.05 0.88 OCTNOV, DECJAN 1.4 OND 7.93 Click for Nov-Mar GWO Phase Space Plot
1965-66 -0.83 -0.75 1.43 JULAUG 2.0 SON, OND 20.44 Click for Nov-Mar GWO Phase Space Plot
1968-69 0.13 0.51 0.85 JANFEB 1.1 DJF, JFM 27.47 Click for Nov-Mar GWO Phase Space Plot
1969-70 0.36 0.41 0.66 OCTNOV 0.9 SON 7.77 Click for Nov-Mar GWO Phase Space Plot
1972-73 -0.10 -0.24 1.83 JUNJUL, JULAUG 2.1 OND, NDJ 21.26 Click for Nov-Mar GWO Phase Space Plot
1976-77 0.29 -0.83 1.02 AUGSEP 0.9 OND 12.31 Click for Nov-Mar GWO Phase Space Plot
1977-78 -0.65 1.01 0.97 SEPOCT, OCTNOV 0.8 OND, NDJ 33.44 Click for Nov-Mar GWO Phase Space Plot
1979-80 0.49 -0.01 0.6 ND, MA, MJ 0.6 NDJ, DJF 26.98 Click for Nov-Mar GWO Phase Space Plot
1982-83 0.94 2.34 2.9 AM 2.2 OND,NDJ, DJF 31.25 Click for Nov-Mar GWO Phase Space Plot
1986-875 0.23 0.02 2.0 MJ87 1.2 NDJ,-JFM 7.66 Click for Nov-Mar GWO Phase Space Plot
1987-885 1.16 1.00 2.0 MJ87 1.7 JAS 12.48 Click for Nov-Mar GWO Phase Space Plot
1991-92 -0.01 0.81 2.0 MA 1.7 DJF 21.00 Click for Nov-Mar GWO Phase Space Plot
1994-95 -0.42 0.77 1.4 SO 1.1 NDJ 24.35 Click for Nov-Mar GWO Phase Space Plot
1997-98 1.82 1.49 2.3, 2.6 MJ97, MA98 2.4 OND, NDJ 31.01 Click for Nov-Mar GWO Phase Space Plot
2002-03 0.05 0.32 1.0, 0.9 JA, ND 1.3 OND 16.49 Click for Nov-Mar GWO Phase Space Plot
2004-05 -0.02 0.75 0.7, 0.8 JA04, FM05 0.7 ASO-NDJ 37.25 Click for Nov-Mar GWO Phase Space Plot
2006-07 0.14 -0.32 0.9 ON 0.9 OND-NDJ 3.21 Click for Nov-Mar GWO Phase Space Plot
2009-10 -0.10 0.30 1.1, 1.3 ON, JF-FM 1.6 NDJ 16.36 Click for Nov-Mar GWO Phase Space Plot
2014-156 -0.52 -0.29 2.2 AS15 1.2 MJJ 8.52 Click for Nov-Mar GWO Phase Space Plot
2015-166 1.34 1.64  2.2 AS15 2.6 NDJ 9.36 Click for Nov-Mar GWO Phase Space Plot
2018-197 -0.43 1.22 0.5, 0.8 AS18, FM19 0.9 OND 17.99 Click for Nov-Mar GWO Phase Space Plot

1. AAM and AAM tendency anomaly data for 1951-52 not available.
2. Continuous warm episode from JFM 1953 to JFM 1954.
3. AAM anomaly is average for Jan-Mar 1958.
4. Continuous warm episode from MAM 1957 to JJA 1958 & OND 1958 to FMA 1959.
5. Continuous warm episode from ASO 1986 to JFM 1988.
6. Continuous warm episode from OND 2014 to AMJ 2016.
7. Data as of March 31, 2019.

Jul-Sep AAM & Nov-Mar AAM: The mean of the global relative atmospheric angular momentum anomaly for the periods July 1 to September 30 amd 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 1979-80. MEI v1 values were last updated December 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.

Monday, 15 April 2019 10:49:50 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Tuesday, 21 November 2017

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. Data for 2017-18 will be updated periodically.

Year ERSST
Version
Nov-Mar
AAM
Peak MEI4 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 v3b -- -1.490 MAYJUN (56) -0.4 Several 9.54 --
1961-62 v2 -0.515 -1.065 DECJAN -0.3 ASO, SON 18.79 Click for Nov-Mar GWO Phase Space Plot
1962-63 v3b -1.264 -0.837 JANFEB -0.4 OND, NDJ 8.38 Click for Nov-Mar GWO Phase Space Plot
1964-65 v5 -1.150 -1.476 JULAUG -0.8 ASO - DJF 13.69 Click for Nov-Mar GWO Phase Space Plot
1967-683 v4 -0.773 -1.106 APRMAY -0.7 JFM 16.58 Click for Nov-Mar GWO Phase Space Plot
1970-71 v5 -0.980 -1.870 MARAPR -1.4 DJF, JFM 12.32 Click for Nov-Mar GWO Phase Space Plot
1971-72 v5 -0.174 -1.439 AUGSEP -1.0 OND 7.17 Click for Nov-Mar GWO Phase Space Plot
1973-74 v5 -1.336 -1.912 DECJAN -2.0 NDJ 14.92 Click for Nov-Mar GWO Phase Space Plot
1974-75 v5 -0.846 -1.230 OCTNOV -0.8 OND 14.35 Click for Nov-Mar GWO Phase Space Plot
1975-76 v5 -0.716 -1.968 SEPOCT -1.7 OND, NDJ 7.22 Click for Nov-Mar GWO Phase Space Plot
1983-84 v5 -1.099 -0.509 JANFEB -1.0 OND 10.43 Click for Nov-Mar GWO Phase Space Plot
1984-85 v5 -0.600 -0.715 APRMAY -1.1 NDJ 12.82 Click for Nov-Mar GWO Phase Space Plot
1988-89 v5 -1.144 -1.501 AUGSEP -1.8 OND, NDJ 8.08 Click for Nov-Mar GWO Phase Space Plot
1995-96 v5 -0.227 -0.597 DECJAN -1.0 SON - NDJ 12.46 Click for Nov-Mar GWO Phase Space Plot
1998-99 v5 -0.544 -1.123 JANFEB -1.6 NDJ, DJF 9.09 Click for Nov-Mar GWO Phase Space Plot
1999-00 v5 -0.784 -1.189 JANFEB -1.7 NDJ, DJF 11.57 Click for Nov-Mar GWO Phase Space Plot
2000-01 v5 -0.801 -.701 OCTNOV -0.7 OND - DJF 17.94 Click for Nov-Mar GWO Phase Space Plot
2005-06 v5 -0.616 -0.575 MARAPR -0.8 NDJ, DJF 13.19 Click for Nov-Mar GWO Phase Space Plot
2007-08 v5 -1.015 -1.579 FEBMAR -1.6 NDJ - DJF 13.53 Click for Nov-Mar GWO Phase Space Plot
2008-09 v5 -0.599 -.723 FEBMAR -0.8 DJF 9.08 Click for Nov-Mar GWO Phase Space Plot
2010-11 v5 -0.598 -1.888 AUGSEP -1.7 SON, OND 20.20 Click for Nov-Mar GWO Phase Space Plot
2011-12 v5 -0.371 -0.980 DECJAN -1.1 SON, OND 8.69 Click for Nov-Mar GWO Phase Space Plot
2016-17 v5 0.088 -0.363 SEPOCT -0.7 ASO - OND 19.00 Click for Nov-Mar GWO Phase Space Plot
2017-185 v5 -0.550 -0.731 JANFEB -1.0 NDJ 4.68 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. ONI did not meet threshold of 5 consecutive overlapping seasons using ERSST v5.
4. MEI values are normalized and may change as new data is added. Specified values were current as of March 6, 2018.
5. Data as of March 31, 2018.

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). Reference Wolter and Timlin, 1993, 1998. MEI values are normalized and may shift as new data is added.

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.

Tuesday, 21 November 2017 14:00:44 (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Sunday, 03 April 2016

Following is a chart comparing the 2015-16 El Nino to warm ENSO episodes that have occurred since 1950. The warm episodes are based on the revised Oceanic Niño Index (ONI) which is calculated using the three month running mean of ERSST.v4 SST anomalies in the Niño 3.4 region with multiple-centered 30 year base periods. Unless noted the warm episodes are those specified in the CPC's tabulation of Cold & Warm Episodes by Season. 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 warm episode.

Year Jul-Sep
AAM
Nov-Mar
AAM
Peak MEI Peak MEI Season Peak
ONI
Peak ONI Season L.A. Rain GWO
Phase Plot
1951-521 -- -- 0.822 JULAUG 0.9 SON 26.21 --
1952-532 -- -- 0.788 APRMAY 0.7 FMA-AMJ 9.46 --
1953-542 -- -- 0.484 AUGSEP 0.8 ASO, SON, OND 11.99 --
1957-583 -- 0.773 1.474 DECJAN, JANFEB 1.7 DJF 21.13 Click for Nov-Mar GWO Phase Space Plot
1958-59 -0.919 -0.206 0.788 JANFEB 0.6 NDJ, DJF, JFM 5.58 Click for Nov-Mar GWO Phase Space Plot
1963-64 0.005 0.046 0.867 OCTNOV, DECJAN 1.2 SON, OND 7.93 Click for Nov-Mar GWO Phase Space Plot
1965-66 -0.826 -0.748 1.436 JULAUG 1.8 OND 20.44 Click for Nov-Mar GWO Phase Space Plot
1968-69 0.130 0.513 0.844 JANFEB 1.0 JFM 27.47 Click for Nov-Mar GWO Phase Space Plot
1969-70 0.358 0.413 0.670 OCTNOV 0.8 ASO, SON, OND 7.77 Click for Nov-Mar GWO Phase Space Plot
1972-73 -0.096 -0.239 1.827 JUNJUL, JULAUG 2.0 OND 21.26 Click for Nov-Mar GWO Phase Space Plot
1976-77 0.284 -0.828 1.029 AUGSEP 0.8 OND,NDJ 12.31 Click for Nov-Mar GWO Phase Space Plot
1977-78 -0.646 1.008 0.993 SEPOCT, OCTNOV 0.8 OND, NDJ 33.44 Click for Nov-Mar GWO Phase Space Plot
1979-804 0.496 -0.013 0.996 NOVDEC 0.6 NDJ, DJF 26.98 Click for Nov-Mar GWO Phase Space Plot
1982-83 0.938 2.337 3.011 FEBMAR 2.1 OND,NDJ, DJF 31.25 Click for Nov-Mar GWO Phase Space Plot
1986-875 0.232 0.019 2.140 APRMAY87 1.2 JFM 7.66 Click for Nov-Mar GWO Phase Space Plot
1987-885 1.153 1.000 1.982 JULAUG 1.6 JAS, ASO 12.48 Click for Nov-Mar GWO Phase Space Plot
1991-92 -0.008 0.808 2.269 MARAPR 1.6 DJF 21.00 Click for Nov-Mar GWO Phase Space Plot
1994-95 -0.422 0.764 1.419 SEPOCT 1.0 NDJ 24.35 Click for Nov-Mar GWO Phase Space Plot
1997-98 1.811 1.481 3.049 JULAUG,AUGSEP 2.3 OND, NDJ 31.01 Click for Nov-Mar GWO Phase Space Plot
2002-03 0.047 0.324 1.199 DECJAN 1.3 OND 16.49 Click for Nov-Mar GWO Phase Space Plot
2004-05 -0.020 0.747 1.055 FEBMAR 0.7 JAS-NDJ 37.25 Click for Nov-Mar GWO Phase Space Plot
2006-07 0.143 -0.322 1.322 OCTNOV 1.0 NDJ 3.21 Click for Nov-Mar GWO Phase Space Plot
2009-10 -0.103 0.303 1.521 JANFEB 1.3 NDJ,DJF 16.36 Click for Nov-Mar GWO Phase Space Plot
2014-156 -0.526 -0.297 0.997, 1.567 MAYJUN14, APRMAY15 0.6 OND, NDJ 8.52 Click for Nov-Mar GWO Phase Space Plot
2015-167 1.313 1.637  2.527 AUGSEP 2.3 NDJ 9.36 Click for Nov-Mar GWO Phase Space Plot

1. AAM and AAM tendency anomaly data for 1951-52 not available.
2. Continuous warm episode from DJF 1952/53 to DJF 1954.
3. AAM anomaly is average for Jan-Mar 1958.
4. Warm episode per ERSST.v4, but not ERSST.v3b.
5. Continuous warm episode from ASO 1986 to JFM 1988.
6. Warm episode per ERSST.v3b, but not ERSST.v4.
7. Data as of April 3, 2016.

Jul-Sep AAM & Nov-Mar AAM: The mean of the global relative atmospheric angular momentum anomaly for the periods July 1 to September 30 amd 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). Reference Wolter and Timlin, 1993, 1998. MEI values are normalized and may shift as new data is added.

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.

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.

Sunday, 03 April 2016 08:46:40 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Tuesday, 28 July 2015

NRL GOES E/W Composite VIS/IR (Day/Night) - Saturday, July 18, 2015 5:00 PM PDT Click
NRL GOES E/W Composite VIS/IR (Day/Night)
Post-tropical remnant low Dolores is west of Baja
Saturday, July 18, 2015 5:00 PM PDT.

Downtown Los Angeles (USC) ended the 2014-2015 rainfall year (July 1 - June 30) with 8.52 inches of rain; well below the normal of 14.93 inches. It was the fourth consecutive year of below normal rainfall in Los Angeles and much of Southern California.

To kick off the new new rainfall year two waves of moisture and instability associated with ex-hurricane Dolores, other tropical sources, and a strong monsoonal flow from Baja resulted in record-setting rainfall in Southern California from Saturday July 18 to Monday July 20.

Constructive interference of the El Nino base state by the active phase of the MJO resulted in negative 200-hPa velocity potential anomalies and enhanced convection in the Eastern Pacific during the first half of July. This appears to have contributed to the rapid development of Dolores from a tropical depression on July 11 into a Category 4 hurricane July 15. Anomalously warm SSTs in the tropical and sub-tropical Eastern Pacific also played a role, helping to maintain the strength of Dolores and increasing the amount of water vapor entrained by the system and transported into Southern California.

Many stations set new records, not only for the date, but for any day in July. Downtown Los Angeles (USC) set rainfall records for the date on Saturday and Sunday and tied Monday's record. Downtown Los Angeles recorded 0.36 inch of rain Saturday. This is more rain than any day in any July since recordkeeping began in 1877. That one day of rainfall even broke the monthly record for July in Los Angeles! Prior to this event the wettest July on record was in 1886, when 0.24 inch was recorded.

There was very heavy rain in the mountains on Sunday, with rain rates exceeding an inch a hour. From 5:15 p.m. to 5:25 p.m. a CBS Radio weather station on Mt. Wilson recorded a half-inch of rain in just 10 minutes!

Though the rain created its own problems -- including flash floods, debris flows and rock slides -- the soaking rains helped quell the Pines Fire near Wrightwood and the North Fire near Cajon Pass. Over the three day period from Saturday to Monday the Big Pines Remote Automated Weather Station (RAWS), near the Pines Fire, recorded 3.12 inches of rain. Several stations in the San Gabriels recorded more than three inches of rain, including Clear Creek and Opids Camp. Here's a NWS compilation of some rainfall totals in the Los Angeles forecast area and the San Diego forecast area.

After dawdling around for several months our on again, off again El Nino is finally firing on all cyclinders and could reach ONI and MEI levels not seen since 1997-98 and 1982-83. The Multivariate ENSO Index (MEI) for May-June was 2.06. This was the third highest value for the season, exceeded only in 1983 (2.2) and 1997 (2.3). It is the second highest for the season during the development phase of an El Nino event. The 2015 April-May-June Oceanic Nino Index (ONI) value of 0.9 was higher than than in 1982 (0.6) and 1997 (0.6). Several dynamical models in the IRI/CPC ENSO Predictions Plume of forecast Nino 3.4 SST anomaly, released July 16, project Nino 3.4 SST anomalies in excess of 2.5°C this fall.

Analysis of correlations of CMAP Precipitation with globally integrated atmospheric angular momentum using ESRL/PSD's Linear Correlations in Atmospheric Seasonal/Monthly Averages tool suggests that precipitation in the southern half of California is more strongly correlated with atmospheric angular momentum (AAM) than with Nino 3.4 SST. For example, compare the correlation of CMAP Precipitation to AAM and to Nino 3.4 SST for Dec-Jan-Feb 1980-2012. Cyclical increases in relative atmospheric angular momentum are often associated with El Ninos. This can be seen in the plots of the Global Wind Oscillation in my El Nino Comparison Chart.

After being negative for 3 1/2 years, the PDO Index has been positive since January 2014. December's PDO value of 2.51 was the highest for that month on record since 1900. June's value of 1.54 was the 13th highest since 1900.

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

 

Tuesday, 28 July 2015 08:07:55 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Monday, 06 July 2015

Following is a chart comparing 2014-15 to warm ENSO episodes that have occurred since 1950. The warm episodes are based on the revised Oceanic Niño Index (ONI) which is calculated using the three month running mean of ERSST.v4 SST anomalies in the Niño 3.4 region with multiple-centered 30 year base periods. Unless noted the warm episodes are those specified in the CPC's tabulation of Cold & Warm Episodes by Season. A description of the parameters follows the chart. With the exception of years prior to 1957, a GWO phase space plot is included for each warm episode.

Year Jul-Sep
AAM
Nov-Mar
AAM
Peak MEI Peak MEI Season Peak
ONI
Peak ONI Season L.A. Rain GWO
Phase Plot
1951-521 -- -- 0.847 JULAUG 0.9 SON 26.21 --
1952-532 -- -- 0.788 APRMAY 0.7 FMA-AMJ 9.46 --
1953-542 -- -- 0.520 AUGSEP 0.8 ASO, SON, OND 11.99 --
1957-583 -- 0.773 1.472 DECJAN, JANFEB 1.7 DJF 21.13 Click for Nov-Mar GWO Phase Space Plot
1958-59 -0.919 -0.206 0.807 JANFEB 0.6 NDJ, DJF, JFM 5.58 Click for Nov-Mar GWO Phase Space Plot
1963-64 0.005 0.046 0.859 OCTNOV, DECJAN 1.2 SON, OND 7.93 Click for Nov-Mar GWO Phase Space Plot
1965-66 -0.826 -0.748 1.477 JULAUG 1.8 OND 20.44 Click for Nov-Mar GWO Phase Space Plot
1968-69 0.130 0.513 0.867 JANFEB 1.0 JFM 27.47 Click for Nov-Mar GWO Phase Space Plot
1969-70 0.358 0.413 0.653 OCTNOV 0.8 ASO, SON, OND 7.77  
1972-73 -0.096 -0.239 1.896 JUNJUL, JULAUG 2.0 OND 21.26 Click for Nov-Mar GWO Phase Space Plot
1976-77 0.284 -0.828 1.024 AUGSEP 0.8 OND,NDJ 12.31 Click for Nov-Mar GWO Phase Space Plot
1977-78 -0.646 1.008 1.006 SEPOCT, OCTNOV 0.8 OND, NDJ 33.44 Click for Nov-Mar GWO Phase Space Plot
1979-804 0.496 -0.013 1.016 NOVDEC 0.6 NDJ, DJF 26.98 Click for Nov-Mar GWO Phase Space Plot
1982-83 0.938 2.337 3.024 FEBMAR 2.1 OND,NDJ, DJF 31.25 Click for Nov-Mar GWO Phase Space Plot
1986-875 0.232 0.019 2.140 APRMAY 1.2 JFM 7.66 Click for Nov-Mar GWO Phase Space Plot
1987-885 1.153 1.000 1.956 JULAUG 1.6 JAS, ASO 12.48 Click for Nov-Mar GWO Phase Space Plot
1991-92 -0.008 0.808 2.269 MARAPR 1.6 DJF 21.00 Click for Nov-Mar GWO Phase Space Plot
1994-95 -0.422 0.764 1.434 SEPOCT 1.0 NDJ 24.35 Click for Nov-Mar GWO Phase Space Plot
1997-98 1.811 1.481 3.005 JULAUG,AUGSEP 2.3 OND, NDJ 31.01 Click for Nov-Mar GWO Phase Space Plot
2002-03 0.047 0.324 1.185 DECJAN 1.3 OND 16.49 Click for Nov-Mar GWO Phase Space Plot
2004-05 -0.020 0.747 1.032 FEBMAR 0.7 JAS-NDJ 37.25 Click for Nov-Mar GWO Phase Space Plot
2006-07 0.143 -0.322 1.299 OCTNOV 1.0 NDJ 3.21 Click for Nov-Mar GWO Phase Space Plot
2009-10 -0.103 0.303 1.524 JANFEB 1.3 NDJ,DJF 16.36 Click for Nov-Mar GWO Phase Space Plot
2014-156 -0.526 -0.297 0.967, 1,567 APRMAY14, APRMAY15 0.6 OND, NDJ 8.52 Click for Nov-Mar GWO Phase Space Plot

1. AAM and AAM tendency anomaly data for 1951-52 not available.
2. Continuous warm episode from DJF 1952/53 to DJF 1954.
3. AAM anomaly is average for Jan-Mar 1958.
4. Warm episode per ERSST.v4, but not ERSST.v3b.
5. Continuous warm episode from ASO 1986 to JFM 1988.
6. Warm episode per ERSST.v3b, but not ERSST.v4.

Jul-Sep AAM & Nov-Mar AAM: The mean of the global relative atmospheric angular momentum anomaly for the periods July 1 to September 30 amd November 1 to March 31 of the following year. Data is from the GWO phase space data file linked on 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). Reference Wolter and Timlin, 1993, 1998. MEI values are normalized and may shift as new data is added.

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.

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 from the GWO phase space data file linked on the Global Synoptic Dynamic Model page of the PSD Map Room Climate Products. Reference Weickmann and Berry, 2008.

Monday, 06 July 2015 10:56:10 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Tuesday, 20 January 2015

Southwestern U.S. Current Departure from Normal Precipitation Since October 1 as of 1/19/2015 12:00 UTC. Click
Current Departure from Normal Precipitation Since October 1
AHPS Precpitation Analysis as of 1/19/2015 12:00 UTC.

After being negative for 3 1/2 years, the PDO Index has been positive since January 2014. December's PDO value of 2.51 is the highest for that month on record (since 1900), exceeding December 2002's value of 2.10 and December 1940's value of 1.96.

Even so, the highly anticipated 2014-15 El Nino continues to dawdle with little ocean-atmosphere coupling and an emphasis on an higher amplitude meridional flows. Due in part to the upwelling phase of a series of oceanic Kelvin waves, equatorial Pacific heat content and SST anomalies have diminished. After having been at or above 0.5 °C for the past twelve weeks OISST.v2 Nino 3.4 SST Anomalies dropped to 0.4 °C for the week centered on January 7, 2015 and as of the week of January 14 was at 0.5 °C.

The Multivariate ENSO Index (MEI) for NOV/DEC has decreased 0.13 SD to +0.58, but has maintained its historic rank (since 1950) at 47. A rank of 46 is the threshold for weak El Nino conditions in the context of the MEI. The FNL Global Wind Oscillation for the past 90 days continues to reflect the lack of definitive atmospheric coupling.

So far this rain season Northern California and the coastal areas of Central and Southern California have fared much better in terms of precipitation than last year. As of today Downtown Los Angeles (USC) precipitation for the water year (beginning July 1) is at 90% of normal and Downtown San Francisco is at 127%.

As this AHPS plot of precipitation since October 1 shows, many areas of California have recorded at least 75% of normal precipitation. Unfortunately the Sierra Nevada is not one of them. While better than last year's dismal 14% of normal on this date, this year's snowpack is currently well below average, and was last reported at 36%. Here is an AHPS plot of precipitation departure since October 1 that shows the deficits in the Sierra Nevada.

At the moment it doesn't look like the snowpack will get much help in the short term. After fending off a little shortwave the blocking ridge is forecast to rebuild to new heights, bringing unseasonably mild weather to much of the West Coast. There does appear to be the possibility of a wildcard low latitude low developing under the block and that could result in some precipitation in Southern California next week. If such a system develops, given the warm state of the Eastern Pacific, it could be wetter than expected. We'll see!

In the early morning hours of Friday, December 12, 2014, a very strong cold front, enhanced with moisture from an atmospheric river, produced a line of strong storms that produced rain rates in the Springs Fire burn area as high as 2 inches per hour. This resulted in widespread flash floods and debris flows in the burn area, much of which is in Pt. Mugu State Park. Mud and debris flows originating from the burn area inundated homes below Conejo Mountain and closed Pacific Coast Highway. This slideshow includes photos of the aftermath of the flash floods and debris flows in Blue Canyon, Sycamore Canyon and Upper Sycamore. The photos were taken on a trail run on December 14, 2014. Also included are some NWS Los Angeles/Oxnard tweets and some additional meteorological images and info.

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

 

Tuesday, 20 January 2015 08:44:31 (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Sunday, 07 December 2014

CNRFC 96 Hr Gridded Precipitation Totals for the Four-Day Period Ending 12/04/2014 4:00 am Click
CNRFC 96 Hr Gridded Precipitation Totals
For the Four-Day Period Ending 12/04/2014 4:00 am.

After being negative for 3 1/2 years, the PDO Index has been positive since January 2014. October's PDO value of 1.49 is the 6th highest for that month since 1900 and comparable to PDO Index values in October 1997, 1957, 1993, and 1987.

PDO/AMO-based Precipitation composites suggest a warm Pacific generally produces more Winter precipitation in California than a cold Pacific. This makes sense. Among other effects a warm Pacific increases evaporation, air temperature, and the amount of water vapor transferred to the atmosphere. This in turn can increase precipitation. Here is a comparison of Pacific SST anomalies at the beginning of December 2014 and December 2013. Mouse over the image to switch to the December 1, 2013 image.

A warm Pacific may have contributed to the amount of precipitation produced in California by a large Pacific upper level low this past week. Two periods of rain were observed in Southern California -- one on Sunday and the other on Tuesday and Wednesday.

Sunday an embedded short wave in the moist southerly flow produced more rain than expected in many areas of Los Angeles. Surprisingly high rain rates and amounts in the Santa Monica Mountains, resulted in debris flows in the Springs Fire burn area that closed PCH. Here's a NWS compilation of some rainfall totals in the forecast area.

Even with the parent low lifting to the north on Tuesday and the 570 mb contour near Santa Barbara, the very moist southerly flow orographic lift and sufficient dynamics produced widespread precipitation in Southern California with some impressive precipitation totals. Tuesday record rainfall for the date occurred at both Downtown Los Angeles and Downtown San Francisco. Yucaipa Ridge in the San Bernardino Mountains recorded a whopping three-day rainfall total of 14.6 inches. Following are three-day rainfall compilations from the NWS Los Angeles/Oxnard and NWS San Diego.

Here are graphics from the CNRFC with gridded precipitation totals for the four day period from early Sunday morning to early Thursday morning for Southern California, the Sierra Nevada and the San Francisco Bay Area. Some preliminary precipitation totals of 5 inches or more are noted.

Equatorial Pacific SSTs continue to rebound with OISST.v2 Nino 3.4 SST Anomalies above 0.5 °C for the past seven weeks and now stand at 1.0 °C for the week centered on November 26, 2014. The Multivariate ENSO Index (MEI) for OCT/NOV has increased 0.35 SD to 0.71, increasing its historic rank (since 1950) from 42 to 47, just within the MEI's weak El Nino threshold. However as noted by the CPC in their December 4, 2014 ENSO Diagnostic Discussion, "the overall atmospheric circulation has yet to show a clear coupling to the anomalously warm waters." The FNL Global Wind Oscillation for the past 90 days continues to reflect the lack of definitive atmospheric coupling

For now the Pacific storm door appears to be open. Most medium-range guidance is suggesting another significant system will be affecting California in the Thursday-Friday timeframe. We'll see!

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

 

Sunday, 07 December 2014 13:33:07 (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Friday, 07 November 2014

SST NINO Region Anomalies from the CPC ENSO Diagnostic Discussion 11/6/2014. Click
SST NINO Region Anomalies
From the CPC ENSO Diagnostic Discussion 11/6/2014.

One thing is very clear; we have a lot to learn about the atmosphere's response to anomalously warm equatorial Pacific SSTs. It's difficult to imagine a better scenario for El Niño development than the conditions seen in the equatorial Pacific earlier this year.

After being negative for 42 out of the previous 43 months, the Pacific Decadal Oscillation (PDO) index turned positive in January 2014 and has remained positive through the summer. Beginning in January and ending in late June the downwelling phase of a very strong Kelvin wave propagated across the Pacific, with upper ocean area-averaged heat content anomaly between 180 and 100W peaking at the end of March. Since January there have been westerly wind bursts and periods of increased low-level westerly zonal wind anomalies of variable duration and extent.

The Oceanic Niño Index (ONI) jumped from -0.5 in the FMA season to -0.1 in MAM, and then to +0.1 in AMJ. During that same period the Multivariate ENSO Index (MEI) jumped from a rank of 35 in MARAPR to 59 in APRMAY -- a value that put it on the doorstep of a strong El Nino ranking. Which all looked supportive of at least a moderate El Nino developing.

But it didn't. After climbing up to 0.6 °C in late May, Nino 3.4 region SST anomalies dropped to below 0.0 °C in late July. Since then a more modest downwelling Kelvin wave has restored some of the basin heat content and Nino 3.4 anomalies have rebounded back to 0.6 °C.

So what's next? While El Nino development still appears to be possible this Winter, it would be one of the two latest developing El Ninos in the record from 1950 to the present -- the other being 1952-53. One possibility is that this year's vacillations are the precursor to the EARLY development of an El Nino event next year.

One worrisome detail is that the Global Wind Oscillation (GWO) has been behaving similarly to the failed El Nino of 2012. Compare this plot of the GWO from June 1 to October 31 of this year to the plot of the GWO from June 1 to October 31, 2012. In both 2014 and 2012 the GWO has shown a neutral or weak La Nina-like response. The GWO for the period June 1 to October 31, 1997 is an example of a definitive atmospheric response to strong El Nino conditions.

On a more positive note, a relatively strong, but fast-moving Pacific cold front and trough resulted in rain and snow in California over Halloween. In the Los Angeles area rainfall amounts generally varied from around 0.3 inch to 0.75 inch or so with isolated amounts as high as about 2.0 inches in the mountains. Here are some tabulated rainfall amounts from around the area from the NWS Los Angeles/Oxnard and NWS San Diego.

The 1981-2010 climate normal average rainfall for Downtown Los Angeles in November is 1.04 inches. Month to date we're about average for the date, and water year to date we're ahead of last year, but about 0.6 inch below normal.

Based on the current GFS and ECMWF forecasts those deficits are probably going to increase over the next two weeks, but it is way too early in the rain season to attribute the dry weather to a continued dry pattern. El Niño or not; dry November or not; the switch from a cold Pacific to a warm Pacific is a significant change and one that some guidance suggests should increase our rainfall. We'll see!

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

 

Friday, 07 November 2014 14:18:36 (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   |