Page 1 of 3 in the LaNina category Next Page
# Wednesday, 18 August 2021

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.

Wednesday, 18 August 2021 11:00:07 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# 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  |   | 
# 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  |   | 
# Saturday, 02 July 2016

Dying Redwoods Malibu Creek State Park Click
Dead and Dying Coast Redwoods Along Century Lake
Malibu Creek State Park

Downtown Los Angeles (USC) finished the 2015-16 rainfall year (July 1 to June 30) with 9.65 inches of recorded precipitation. This is about 65% of the 1981-2010 normal of 14.93 inches. This was the fifth consecutive year of below normal rainfall for Downtown Los Angeles, with a cumulative rainfall deficit of 35.86 inches --nearly three feet!

Observable impacts of the drought are widespread. Trees have been particularly hard hit. Dead trees can be seen along city streets, in parks, and throughout the open space areas and wildlands of Southern California. The dead and dying 100+ year old coast redwoods at Malibu Creek State Park are an example.

Most climate outlooks are forecasting La Nina conditions to develop over the Northern Hemisphere summer. Historically La Ninas have "on average" resulted in below normal precipitation in Southern California. But historical composites can be misleading. During the last five La Nina episodes (1999-00, 2000-01, 2007-08, 2010-11, 2011-12) Downtown Los Angeles (USC) has averaged 14.39 inches of rain, which is 96% of normal.

Even during one of three strongest El Ninos on record, precipitation outlooks based on historical composites and analogs didn't perform well in Southern California. Given the somewhat more variable rainfall in Southern California during La Ninas, to determine the winter precipitation outlook you might as well flip a three-sided coin.

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

Saturday, 02 July 2016 13:39:23 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Sunday, 20 October 2013

CPC Dec-Jan-Feb Precipitation Outlook Click
CPC Dec-Jan-Feb Precipitation Outlook
Released October 17, 2013.

Updated November 5, 2013. My mistake -- a spreadsheet range error -- thanks for the heads up Reg! The driest January 1 to November 1 for Downtown Los Angeles was in 1972 with 0.92 inch. Here are the driest ten years for that period:

1. 1972 0.92
2. 2002 1.62
3. 1984 1.93
4. 1961 2.37
5. 1971 2.39
6. 1947 2.45
7. 2013 2.78
8. 1894 2.89
9. 1953 2.89
10. 2007 3.37

An energetic upper level low brought the first widespread precipitation of the rain season to Southern California October 9, with rain at the lower elevations and some snow in the local mountains. Rainfall amounts varied widely, ranging from a trace in some areas to over an inch in the mountains.

Downtown Los Angeles (USC) recorded only 0.04 inch for the storm, bringing the water year rainfall total to 0.13 inch, which is 0.31 inch below normal. Downtown Los Angeles has recorded only 2.76 inches of rain since January 1. This is one of the driest January 1 - October 20 in Los Angeles over the past 135 years! To get out of the bottom ten for calendar year rainfall Los Angeles needs about 3.5 inches of rain by December 31. Normal rainfall for November is 1.04 inches and for December is 2.33 inches.

For months I've been monitoring climate data and forecasts looking for something on which to base a 2013-14 Winter precipitation Outlook. Historically ENSO has played the major role in Southern California rain season weather, with El Nino conditions generally producing wetter weather and La Nina conditions generally drier. But ENSO conditions are currently Neutral and are expected to remain so through the end of the year.

Most climate models forecast slow warming of SSTs in the equatorial Pacific (NINO 3.4 region) over the next several months, but at this time of the year it would be very unusual to have substantial warming. The CPC/IRI ENSO Forecasts from IRI's October Quick Look indicate the probability of an El Nino developing before the end of the year is less than 20% -- and 20% seems high.

One computer model that at times has been forecasting above average precipitation in Southern California this Winter is the Climate Forecast System version 2 (CFSv2). The CFSv2 is fully coupled ocean-atmosphere-land-sea ice model used to forecast parameters such as sea surface temperature, temperature and precipitation rate. While skillful at predicting tropical SSTs, the CFSv2 generally performs very poorly when forecasting precipitation over land, so forecasts such as this earlier one for Dec-Jan-Feb must be viewed somewhat skeptically.

Another glass half-full observation is that the Madden-Julian Oscillation (MJO) has been relatively active this year and if this activity continues it provides recurring opportunities for enhanced U.S. West Coast precipitation. The downside is that it can result in periods of dry weather as well.

With the ocean and atmosphere neutral there's just not much on which to base a rain season forecast. As a result of the government shutdown the release of the official NOAA 2013-14 Winter Outlook has been delayed until November. The October CPC outlook is usually the basis of the initial official NOAA U.S. Winter Outlook. The U.S. Dec-Jan-Feb Precipitation Outlook, released October 17, calls for an equal chance of below average, average, or above average precipitation for all of California. We'll see!

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

Sunday, 20 October 2013 15:31:26 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Saturday, 29 September 2012

In a post last June I mentioned that the atmosphere wasn't responding to warming Pacific equatorial SSTs. At that time normalized relative AAM values had dropped to around -2 sigma. Although El Nino-like SST conditions developed in the equatorial Pacific in July and persisted in August, the atmospheric component (AAM) did not follow suit. The average AAM for the period July-September was less than any other El Nino year going back to 1950. (See chart below.)

Following a relative rapid 2 sigma increase over a period of six months, the July/August value of the Multivariate ENSO Index (MEI) dropped from 1.139 to 0.579, and its rank for the season dropped from just below a 'strong' El Nino to just below a 'weak' El Nino. Over the last month SST Anomaly in Nino Region 3.4 has dropped 0.6°C. A review of the ONI record reveals that a drop in the index, which is based on a 3 month running mean of Nino 3.4 anomaly, has not occurred before the Sep-Oct-Nov season during a warm episode.

As of mid September most models were still forecasting development of weak El Nino conditions. The IRI/CPC Plume-based ENSO Forecast puts the probability of El Nino conditions in the Sep-Oct-Nov season at a little over 80%! The probability of Neutral conditions is pegged at a little under 20%. The chance of returning to La Nina conditions is considered virtually nil. Going back to 1950, year two La Nina conditions almost always transition either back to La Nina conditions or to El Nino conditions. Depending on the climatology used there is either one (1985-86) or no cases of a transition to Neutral conditions from a second year La Nina.

Many dynamical model MJO forecasts are predicting a developing MJO signal in the Western Pacific, and that appears to be occurring. Velocity potential loops and Pacific Basin stitched satellite imagery show enhanced convection west of the date line, and today's MJO phase space plot from CAWCR/BOM shows a signal beginning to emerge. On the wind side, Mountain torques are over +4 sigma and Coriolis torque is at -2 sigma. Whether the (apparently) emerging MJO will help reboot our fading El Nino remains to be seen.

Update Friday, October 5, 2012. Eastward-propagating MJO-like signal didn't evolve as forecast by GFS (and several other models). Here's today's MJO phase space plot from CAWCR/BOM. Large swings in the magnitude of Mountain and Coriolis torques have continued. Relative AAM remains at about -1 sigma. The Early October CPC/IRI Consensus Probabilistic ENSO Forecast indicates an increasing chance of Neutral conditions developing over the next several months, but still gives an edge to El Nino conditions developing before the end of 2012.

Following is a chart comparing 2012-13 to warm ENSO episodes that have occurred since 1950. The warm episodes are based on the revised Oceanic Niño Index (ONI) based on multiple-centered 30 year base periods and 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 -- -- 0.853 JULAUG 1.2 SON 26.21 --
1952-533 -- -- 0.840 APRMAY 0.7 MAM 9.46 --
1953-543 -- -- 0.522 AUGSEP 0.8 ASO,SON,OND 11.99 --
1957-58 -- 0.773 1.473 DECJAN, JANFEB 1.8 NDJ, DJF 21.13 Click for Nov-Mar GWO Phase Space Plot
1958-592 -0.919 -0.206 0.803 JANFEB 0.6 NDJ, DJF,JFM 5.58 Click for Nov-Mar GWO Phase Space Plot
1963-64 0.005 0.046 0.857 OCTNOV, DECJAN 1.4 OND 7.93 Click for Nov-Mar GWO Phase Space Plot
1965-66 -0.826 -0.748 1.483 JULAUG 1.9 SON,OND 20.44 Click for Nov-Mar GWO Phase Space Plot
1968-694 0.130 0.513 0.868 JANFEB 1.1 DJF, JFM 27.47 Click for Nov-Mar GWO Phase Space Plot
1969-704 0.358 0.413 0.644 OCTNOV 0.9 SON,OND 7.77  
1972-73 -0.096 -0.239 1.886 JUNJUL, JULAUG 2.1 OND,NDJ 21.26 Click for Nov-Mar GWO Phase Space Plot
1976-77 0.284 -0.828 1.027 AUGSEP 0.8 OND,NDJ 12.31 Click for Nov-Mar GWO Phase Space Plot
1977-78 -0.646 1.008 1.007 SEPOCT, OCTNOV 0.8 OND, NDJ 33.44 Click for Nov-Mar GWO Phase Space Plot
1982-83 0.938 2.337 3.037 FEBMAR 2.2 NDJ, DJF 31.25 Click for Nov-Mar GWO Phase Space Plot
1986-875 0.232 0.019 2.122 APRMAY 1.3 JFM 7.66 Click for Nov-Mar GWO Phase Space Plot
1987-885 1.153 1.000 1.951 JULAUG 1.6 JAS, ASO 12.48 Click for Nov-Mar GWO Phase Space Plot
1991-92 -0.008 0.808 2.271 MARAPR 1.6 DJF 21.00 Click for Nov-Mar GWO Phase Space Plot
1994-95 -0.422 0.764 1.434 SEPOCT 1.2 NDJ 24.35 Click for Nov-Mar GWO Phase Space Plot
1997-98 1.811 1.481 3.001 JULAUG,AUGSEP 2.4 OND 31.01 Click for Nov-Mar GWO Phase Space Plot
2002-03 0.047 0.324 1.184 DECJAN 1.3 OND,NDJ 16.49 Click for Nov-Mar GWO Phase Space Plot
2004-05 -0.020 0.747 1.018 FEBMAR 0.7 JAS-NDJ 37.96 Click for Nov-Mar GWO Phase Space Plot
2006-07 0.143 -0.322 1.289 OCTNOV 1 OND, NDJ 3.21 Click for Nov-Mar GWO Phase Space Plot
2009-10 -0.103 0.303 1.520 JANFEB 1.6 NDJ,DJF 16.36 Click for Nov-Mar GWO Phase Space Plot
2012-136 -0.951 0.296 1.139 JUNJUL 0.6 SON 5.85 Click for Nov-Mar GWO Phase Space Plot

1. AAM and AAM tendency anomaly data for 1951-52 not available.
2. AAM anomaly is average for Jan-Mar 1958.
3. Continuous warm episode from DJF 1952/53 to JFM 1954.
4. Continuous warm episode from JAS 1968 to DJF 1969/70.
5. Continuous warm episode from JAS 1986 to JFM 1988.
6. Data as of May 8, 2013.

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 change 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 water year precipitation total in inches for Downtown Los Angeles (USC). Reference NWS Los Angeles/Oxnard Downtown Los Angeles Climate Page, 1921-2006 Water Year Rainfall.

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.

Saturday, 29 September 2012 15:15:07 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Saturday, 30 June 2012

TAO/TRITON Time-Longitude Plot SST and Anomaly Click
TAO/TRITON Time-Longitude Plot of SST and Anomaly
Saturday, June 30, 2012

Downtown Los Angeles (USC) will end the the 2011-2012 water year (July 1 to June 30) having recorded 8.69 inches of rain. This is about 58% of the 1981-2010 normal of 14.93 inches. The deficit of 6.24 inches is a little more than the 5-6 inch deficit recorded in a selection of similar second year La Nina years. According to data compiled by the NWS Santa Barbara will end the water year at about 66% of normal; Camarillo/Oxnard at 57%; Burbank Airport at 51%; LAX at 59%; and Long Beach Airport at 62%.

This TAO/Triton plot of Pacific equatorial SST and anomaly clearly depicts the evolution of our two year La Nina and the recent transition to warmer conditions. Is an El Nino in the works for this Winter? According to the Multivariate ENSO Index (MEI) a transition to El Nino conditions may already be underway. The April/May value of the MEI was +0.706. This is already within the range of a weak El Niño ranking. In his June 6 discussion of the MEI climatologist Klaus Wolter noted the last month's increase in the MEI was the 6th highest increase for this time of year since 1950. He also pointed out that it was the 4th monthly increase of this caliber in a row -- second only to the record of six consecutive large monthly increases in 1997 at the beginning of the mega El Nino of 1997-98. It will be very interesting to see if the string of large increases in the MEI continues with the May/June value.

While the ocean seems to be on board with the El Nino idea, the atmosphere appears to be balking -- at least for the moment. As of June 24, the AAM component of the GWO was down around -2.0, which is nearly as low as it's been during year two of the 2010-2012 La Nina. A positive value of AAM is generally associated with El Nino conditions.

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

Saturday, 30 June 2012 16:27:44 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Thursday, 29 March 2012

NRL GOES-15 Visible/IR Satellite Image from Sunday, March 25, 2012 at 1:31 pm PDT Click
NRL GOES-15 Visible/IR Satellite Image
Sunday, March 25, 2012 at 1:31 pm PDT

Low pressure "alow and aloft" and associated surface boundaries resulted in some higher than expected rainfall totals Sunday. Gauges in the Santa Monica Mountains generally recorded from 2-3 inches of rain, Valleys and the Metro area 1-2 inches, and Los Angeles County mountains 1-2.5 inches. Here are some preliminary rainfall totals from around the area compiled by the NWS, and a snapshot of a Ventura County Watershed Protection District Google Map with some additional rainfall totals.

Downtown Los Angeles (USC) recorded 0.95 inch for the storm, bringing the 2011-2012 water year total to 6.93 inches. This boosts the water year total to 51% of normal. The wet weather the last two weekends makes March the wettest month of the rain season to date at Los Angeles. It may have taken the edge off a very dry rain season for the moment, but rainfall totals the past 30 days have still been below normal in much of Southern California and additional rainfall would really help.

The good news is it looks like the current progressive pattern of West Coast troughs will continue into April. While at the moment it appears the next trough in the series won't produce more than a smattering of rain south of Pt. Conception, the ECMWF has been relatively consistent in bringing in a system similar to our last storm weekend after next. That's a long way out, and the GFS and GEFS don't agree with the ECMWF, but we'll see!

Update 04/02/12. Saturday's system produced a little more rain than expected south of Pt. Conception. Downtown Los Angeles (USC) recorded 0.04 inch for the storm, bringing the 2011-2012 water year total to 6.97 inches. Here are some rainfall totals from around the area compiled by the NWS. At the moment it looks like a disturbance rotating around a large Gulf of Alaska low will probably not elongate and deepen the low enough to produce rain in Southern California, but will result in cooler temperatures Wednesday and Thursday. Higher pressure is forecast to build in behind the trough, with a warming trend forecast through Easter weekend.

According to the Australian Bureau of Meteorology ENSO Wrap-up, issued March 27, the 2011–12 La Niña event has ended, with key indicators returning to neutral levels.

The IRI/CPC mid-March plume of forecasts made by dynamical and statistical models for SST in the Nino 3.4 region suggest ENSO Neutral conditions will persist through boreal autumn 2012. However, as climatologist Klaus Wolter points out, all ten of the two-year La Niña events between 1900 and 2009 either continued as a La Niña event for a third year (four of ten), or switched to El Niño (six of ten), with none of them becoming ENSO-neutral.

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

Thursday, 29 March 2012 10:32:16 (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Sunday, 26 February 2012

ESRL/PSD Analog 8-14 Day Probabilistic Precipitation Forecast Click
ESRL/PSD Analog 8-14 Day Probabilistic Precipitation Forecast
Probability of more than 25mm precipitation from 03/04/12 to 03/10/12.

Wednesday Downtown Los Angeles' water year rainfall total fell below 50% of normal for the date. With only 5.22 inches of rain in the bucket it looks like we're headed toward the driest rain season since the record-setting dry water year of 2006-2007, when a meager 3.21 inches was recorded. If Los Angeles ends the rain year (June 30) with less than 7.16 inches of precipitation, the 2011-2012 water year would be one of the ten driest on record.

It's been dry throughout most of Southern California and much of the state. According to data compiled by the NWS Burbank's water year total now stands at a paltry 34% of normal; Long Beach 49% of normal; Camarillo 42% of normal; Santa Barbara 56% of normal; and Paso Robles 49% of normal. Southernmost California has fared a little better with San Diego at about 79% of normal for the date. Central California rainfall is also well below average with San Francisco at 35% of the normal, San Jose at 26% and Sacramento at 40%.

I received an email recently from a reader asking if I thought a March Miracle was likely this year. Keeping in mind the chaotic nature of weather, and that low probability events do sometimes occur, the short answer is that I don't think it's likely we'll see higher than normal rainfall this March.

In a post in early October I discussed what the impact of a second year La Nina might be on 2011-12 Winter precipitation in the continental U.S. For a selection of seven second year La Ninas the coastal Southern California climate division recorded about 5 to 6 inches less precipitation than normal for the period November through March. If we take a look at March rainfall in that same selection of second year La Ninas, four of the seven recorded less than 0.5 inch rain in March, and only one was well above average -- 4.83 inches in March 1975.

Current outlooks are not favorable for higher than average March precipitation. The Climate Prediction Centers 6-10 Day Precipitation Outlook, 8-14 Day Precipitation Outlook, and One Month Precipitation Outlook all indicate below normal precipitation in Southern California. The ESRL/PSD Analog Probabilistic Precipitation Forecast is also dry in the 6-10 and 8-14 day outlook period, and the PSD Ensemble Spread does not look encouraging.

On the climate side of things the active phase of the MJO has been stalled in the Indian Ocean, but the 15-day ensemble ECMWF and several models forecast increased amplitude and eastward propagation. As a result of strong negative East Asian and Tropical torque events, relative atmospheric angular momentum is dropping like a rock, with the GWO taking a big dive into La Nina territory. Should the MJO continue to propagate and AAM increase over the next 2 weeks, perhaps we'll see the scenario necessary to generate an extended Pacific jet strong enough to impact the West Coast.

Monday its looking like we may get a little rain and possibly some lower elevation snow. Goes soundings and model data indicate the Pacific system is moisture-starved, but it is quite cold and is forecast to have strong dynamics. A GOES sounding near the systems core showed a 500mb temp of -30°C. Precipitable water values in the circulation around the low were around 0.6 inch. With such cold air aloft, and strong system dynamics, strong convection is a possibility. We'll see!

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

Sunday, 26 February 2012 15:37:30 (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Tuesday, 03 January 2012

Following is a chart comparing the 2011-12 La Nina to other cold ENSO episodes that have occurred since 1949. With the exception of 1961-62 and 2008-09 the cold episodes are based on the Oceanic Niño Index (ONI) and are those specified in the CPC's tabulation of Cold & Warm Episodes by Season. A description of the parameters follows the chart. A GWO phase space plot is included for those cold episodes for which AAM data is available. Data for 2011-12 will be updated periodically.

Year Nov-Mar
AAM
Peak MEI4 Peak MEI Season Peak
ONI
Peak ONI Season L.A. Rain GWO
Phase Plot
1949-501,2 -- -1.423 APRMAY -1.7 DJF 9.94 --
1950-511 -- -1.247 NOVDEC -1.0 NDJ, DJF 8.21 --
1954-551 -- -1.578 MAYJUN (54) -1.2 ASO 11.94 --
1955-561 -- -2.276 MAYJUN (55) -2.0 OND 16.00 --
1956-571 -- -1.516 MAYJUN (56) -0.9 SON, OND 9.54 --
1961-623 -0.513 -1.093 DECJAN -0.6 ASO, SON 18.79 Click for Nov-Mar GWO Phase Space Plot
1962-63 -1.259 -0.843 JANFEB -0.7 OND, NDJ 8.38 Click for Nov-Mar GWO Phase Space Plot
1964-65 -1.145 -1.496 JULAUG -1.2 SON, OND 13.69 Click for Nov-Mar GWO Phase Space Plot
1967-68 -0.770 -1.060 APRMAY -0.9 JFM 16.58 Click for Nov-Mar GWO Phase Space Plot
1970-71 -0.976 -1.898 MARAPR -1.3 DJF, JFM 12.32 Click for Nov-Mar GWO Phase Space Plot
1971-72 -0.173 -1.463 AUGSEP -1.0 OND 7.17 Click for Nov-Mar GWO Phase Space Plot
1973-74 -1.331 -1.942 DECJAN -2.1 NDJ 14.92 Click for Nov-Mar GWO Phase Space Plot
1974-75 -0.842 -1.255 OCTNOV -0.9 OND 14.35 Click for Nov-Mar GWO Phase Space Plot
1975-76 -0.713 -2.000 SEPOCT -1.7 OND, NDJ 7.22 Click for Nov-Mar GWO Phase Space Plot
1984-85 -0.597 -0.743 APRMAY -1.1 NDJ 12.82 Click for Nov-Mar GWO Phase Space Plot
1988-89 -1.139 -1.591 AUGSEP -1.9 OND, NDJ 8.08 Click for Nov-Mar GWO Phase Space Plot
1995-96 -0.227 -0.644 DECJAN -0.7 OND to JFM 12.46 Click for Nov-Mar GWO Phase Space Plot
1998-99 -0.541 -1.233 JANFEB -1.4 NDJ, DJF 9.09 Click for Nov-Mar GWO Phase Space Plot
1999-00 -0.781 -1.242 JANFEB -1.6 NDJ, DJF 11.57 Click for Nov-Mar GWO Phase Space Plot
2000-01 -0.795 -.755 OCTNOV -0.7 NDJ 17.94 Click for Nov-Mar GWO Phase Space Plot
2007-08 -1.010 -1.631 FEBMAR -1.4 DJF, JFM 13.53 Click for Nov-Mar GWO Phase Space Plot
2008-093 -0.596 -.783 SEPOCT -0.8 DJF 9.08 Click for Nov-Mar GWO Phase Space Plot
2010-11 -0.596 -2.037 AUGSEP -1.4 SON, OND, NDJ 20.20 Click for Nov-Mar GWO Phase Space Plot
2011-125 -0.370 -1.046 DECJAN -1.0 OND, NDJ 8.19 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.
4. MEI values are normalized and may change as new data is added. Specified values were current as of April 24, 2012.
5. Data as of April 24, 2012.

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. 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 change 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.

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

L.A. Rain: The water year precipitation total in inches for Downtown Los Angeles (USC). Reference NWS Los Angeles/Oxnard Downtown Los Angeles Climate Page, 1921-2006 Water Year Rainfall.

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.

Tuesday, 03 January 2012 07:46:46 (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Wednesday, 23 November 2011

Click
GOES-11 Water Vapor Image
Sunday, November 20, 2011 - 11:30 am PST

For the past two years Los Angeles has recorded above normal rainfall over the first six months of the water year (Jul. 1 to Dec. 31). So far this year is following suit.

After a record-setting storm in early October in which Downtown Los Angeles (USC) recorded over an inch or rain, a series of upper level troughs have continued to bump up the rainfall total. The systems have tended to be amplifying upper level troughs that split, typically transforming the southern half of the trough into a difficult-to-forecast cut-off upper level low. The resulting cut-off lows have then tracked over, along, or off the Southern California coast producing varying amounts of rain.

Sunday's system was the fourth to produce measurable rain in Los Angeles this November. A strong cold front produced very heavy rain, resulting in flooded streets and highways and resulting in a host of other weather-related problems. In the middle of it all runners in the PCTR Santa Monica Mountains 9K, 18K, 30K and 50K were running distances up to 31.5 miles on the trails of Pt. Mugu State Park.

Downtown Los Angeles (USC) recorded 0.90 inches for the storm, bringing the water year total to 2.75 inches. This is 1.11 inch above the new 1981-2010 normal for rainfall from July 1 through November 22. Here are some additional (preliminary) precipitation totals from around the area, compiled by the NWS Los Angeles/Oxnard. More than an inch above normal sounds like a lot, but as of today only guarantees Los Angeles precipitation will be above normal through December 12.

Back on July 1 NOAA released the new 1981-2010 climate normals, replacing the 1971-2000 normals that have been used this past decade. Normals serve as a 30 year baseline average of climate variables such as monthly and annual maximum, minimum, and mean temperature; and monthly and annual total precipitation. For example, Downtown Los Angeles' new normal annual precipitation total is now 14.93 inches, down from the 15.14 inches we've been using.

After dropping to -0.503 for July/August, and then to -0.772 for August/September, the September/October value of the Multivariate ENSO Index (MEI) has dropped a bit more to -.968 sigma. This is well within La Nina territory, but almost one sigma less than last year's September/October value. Plots of the Global Wind Oscillation (GWO) for July 1 to November 19, 2011 and the same period last year illustrate the year-to-year difference in the atmosphere's response to La Nina conditions. So far, this year's response is consistent with a more active MJO and a shift toward a more neutral ENSO state.

While there's still a chance of rain in Southern California Thanksgiving Day, the forecast is looking better than it did a few days ago when rain was considered likely. The difficulty in the forecast is yet another upper level trough splitting into a cut-off upper level low. The 12z NAM forecasts the low to remain offshore on Thanksgiving Day, and move into Northern Baja by the late afternoon. The 09z SREF puts the probability of more than 0.01 inch of rain in coastal Southern California for the 12 hours ending 4:00 pm Thursday at 10% - 30% and the chance of more than 0.10 inch of rain at around 10%. A shift in the track of the low toward the coast would significantly increase the chance of rain. We'll see!

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

Wednesday, 23 November 2011 08:47:53 (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Saturday, 08 October 2011

Click
GOES-11 Water Vapor Image
Wednesday, October 5, 2011 - 11:30 am PDT

An unseasonably deep upper level low, unusually strong 170+ kt Pacific jet, and associated cold front combined to produce record-setting rainfall in Southern California Wednesday, October 5. Rainfall totals exceeded 1.0 inch in many areas.

Downtown Los Angeles (USC) recorded 1.15 inches, setting a new record for the date, and kick-starting the area's rainy season to 0.78 inch above normal. Rainfall records for the date were also set for LAX, Long Beach, Camarillo, Santa Barbara and several other locations. It was the first measurable rainfall at Los Angeles since June 17. Here are some preliminary precipitation totals from the NWS Los Angeles/Oxnard,NWS San Joaquin Valley/Hanford and NWS San Diego.

Enhanced convection in the Western Pacific associated with active phase of the MJO, and an extension of the North Pacific Jet caused by a positive East Asian mountain torque event appeared to have contributed to the unseasonable amount of rainfall. As observed by Ed Berry (Atmospheric Insights, Dec. 30, 2007), "...the MJO itself does not generate enough extratropical westerly wind flow to allow the East Asian jet to impact the USA west coast. A strong positive East Asian mountain torque needs to be involved, on average."

The increase in relative AAM shown by the GWO not withstanding, La Nina conditions appear to be consolidating in the equatorial Pacific. This four month sequence of Pacific Ocean Equatorial Temperature anomaly cross sections shows substantial subsurface cooling from July 11 to September 11. The Multivariate ENSO Index (MEI) has dropped from -0.5 for July/August to -0.8 for the August/September season. This drops the MEI from a rank of 16th last month to 13th this month, just above the quintile definition of a moderate La Niña ranking. Last year the MEI for August/September ranked 1st in the record since 1950. This TAO time-longitude plot of SST and SST anomaly shows less cooling than last year on this date.

To get an idea of what the impact of a second year La Nina might be on 2011-12 Winter precipitation in the continental U.S., the ESRL/PSD US Climate Division Dataset Mapping Page was used to construct a map of US composite precipitation anomalies for November to March for year two La Ninas since 1949. The years included were based primarily on MEI rankings, and include 1950-51, 1955-56, 1962-63, 1971-72, 1974-75, 1999-2000 and 2008-09. The base period was 1971-2000.

For this selection of years the coastal Southern California climate division recorded about 5 to 6 inches less precipitation than normal for the period November through March. The percent of normal water year rainfall recorded at Downtown Los Angeles (USC) ranged from a low of 47% (1971, 7.17"), to a high of 106% (1955, 16.00"). The average rainfall at Los Angeles for these years was 70.5% of normal, or 10.7".

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

Saturday, 08 October 2011 14:05:22 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   |