# 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 -- -1.261 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 -1.087 DECJAN -0.3 ASO, SON 18.79 Click for Nov-Mar GWO Phase Space Plot
1962-63 v3b -1.264 -0.863 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 -1.939 DECJAN -2.0 NDJ 14.92 Click for Nov-Mar GWO Phase Space Plot
1974-75 v5 -0.846 -1.251 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 -0.529 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 -0.612 DECJAN -1.0 SON - NDJ 12.46 Click for Nov-Mar GWO Phase Space Plot
1998-99 v5 -0.544 -1.140 JANFEB -1.6 NDJ, DJF 9.09 Click for Nov-Mar GWO Phase Space Plot
1999-00 v5 -0.784 -1.210 JANFEB -1.7 NDJ, DJF 11.57 Click for Nov-Mar GWO Phase Space Plot
2000-01 v5 -0.801 -.714 OCTNOV -0.7 OND - DJF 17.94 Click for Nov-Mar GWO Phase Space Plot
2005-06 v5 -0.616 -0.575 NOVDEC, 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 -.726 SEPOCT -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 -0.993 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   -0.339           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 April 24, 2012.
5. Data as of November 30, 2017. Data for 2017-18 will be updated periodically.

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  |   | 
# Friday, 30 June 2017

TAO/TRITON Five-Day SST - June 2016 to June 2017 Click
TAO/TRITON Five-Day SST
June 2016 to June 2017

Downtown Los Angeles (USC) finished the 2016-17 rainfall year (July 1 to June 30) with 19.00 inches of recorded precipitation. This is about 127% of the 1981-2010 normal of 14.93 inches. This was the first rain year with above normal precipitation at Los Angeles since 2009-2010, when 20.2 inches was recorded.

As of May 2017 the Pacific Decadal Oscillation Index has been positive (warm) since January 2014 -- a record 41 consecutive months. The previous record streak was 36 months, from August 1991 to July 1994.

Most climate outlooks are projecting ENSO Neutral conditions are favored to persist into the Northern Hemisphere fall, with a lesser chance of weak El Nino conditions developing over that period. Perhaps supporting the notion of El Nino development, the April-May value of the Multivariate ENSO Index (MEI) increased by 0.69 standard deviations from 0.77 to 1.46. This is solidly within the index's El Nino ranking and at the threshold of a strong El Niño ranking. According to Klaus Wolter, the increase over the last three months is the second largest on record for this time of year, exceeded only by 1997. We'll see if ENSO conditions remain neutral or some form of ENSO warming (Central Pacific?) takes place.

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

Friday, 30 June 2017 18:44:36 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Tuesday, 24 January 2017

California Percent of Normal Precipitation for July 1 to January 22, 2017 (WRCC) Click
California Percent of Normal Precipitation (WRCC)
July 1, 2016 to January 22, 2017

Update on February 2, 2017. Downtown Los Angeles has ended January 2017 with 8.38 inches of rain. This is 269% of the normal January rainfall total of 3.12 inches. The preliminary Rain Year precipitation total for Downtown Los Angeles for July 1 through January 31, 2017 is 14.33 inches, which is 193% of the normal amount of 7.44 inches. Here is an updated California Percent of Normal Precipitation map from the Western Regional Climate Center for July 1, 2016 to January 31, 2017.

On the heels of a wet December, a series of Pacific storms have resulted in the wettest start to the Rain Year (July 1 - June 30) and Water Year (October 1 to September 30) since the very wet year of 2004-2005.

The six day period from January 18-23 was particularly wet, with three storms producing a total of 5.53 inches of rain at Downtown Los Angeles (USC). Here are some preliminary 7-day precipitation totals from around the area from the Ventura County Watershed Protection District.

The last system of the series, which brought very heavy precipitation to the area on Sunday, was associated with a well-defined atmospheric river. Precipitation totals in the Los Angeles area for the storm generally ranged from about 2 to 5 inches. According to the NWS, new rainfall records for January 23 were set at Los Angeles Airport (2.94 inches), Camarillo (2.74 inches) and Long Beach Airport (3.97 inches). The rainfall at Long Beach Airport was the most ever recorded in a day at that location. Here are some precipitation totals from around the area compiled by the NWS Los Angeles/Oxnard and NWS San Diego.

As of yesterday Downtown Los Angeles (USC) has recorded 14.33 inches of rain for the Rain Year. This is 217% of the normal amount of 6.65 inches for the date, and 97% of the normal amount of rainfall for an entire year. Assuming we don't get any more rain this January, the 8.38 inches recorded will work out to 269% of the normal amount for the month.

The California Cooperative Snow Surveys Snow Water Equivalents report for today puts the snowpack for the date at an average 197% of normal. That's two times the normal amount.

A little precipitation has crept back into the GFS, GEFS and ECMWF forecasts for the Los Angeles area the first week of February. We'll see!

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

Tuesday, 24 January 2017 19:10:12 (Pacific Standard Time, UTC-08:00)  #    Disclaimer  |   | 
# Tuesday, 27 December 2016

California Percent of Normal Precipitation for July 1 to December 26, 2016 (WRCC) Click
California Percent of Normal Precipitation (WRCC)
July 1, 2016 to December 26, 2016

As of today Downtown Los Angeles (USC) December rainfall is 1.75 inches above the monthly normal of 2.33 inches. Not since the beginning of the drought has Los Angeles experienced such a wet December. The 4.08 inches of rain recorded so far this month is the most since December 2010 and the most for any month since January 2010.

Since the Rain Year began July 1, 5.48 inches of rain has fallen at Downtown Los Angeles (USC). This is more than an inch above the normal July-December rainfall of 4.32 inches. It is the best start to the Rain Year (Jul 1-Jun 30) and Water Year (Oct 1-Sep 30) since 2010.

While the rain is good news, this graphic from the Western Regional Climate Center shows that the Jul-Dec precipitation in some areas of Southern California is still below normal.

Forecasting how the cut off upper level low currently spinning offshore southwest of Los Angeles and a developing upstream trough interact is a tough task, even for a supercomputer. The trough is expected to propel the low in our general direction and then replace/absorb it. Add to the mix the possibility of pulling up some sub-tropical moisture (or not) and the forecast becomes even trickier. Guess we'll see!

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

Tuesday, 27 December 2016 15:50:30 (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, 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  |   | 
# Thursday, 22 October 2015

KSOX NEXRAD LEVEL-III Radar Instantaneous Precipitation Rate for Lake Hughes - Elizabeth Lake Area at 3:30 pm October 15, 2015. Click
NEXRAD LEVEL-III Radar Instantaneous Precipitation Rate
Lake Hughes - Elizabeth Lake Area at 3:30 pm October 15, 2015 (KSOX)

Following a circuit through Arizona, Mexico and the Eastern Pacific that started in Southern California on October 5, a moisture-laden upper low moved into SoCal for a second time Thursday, October 15.

On the second go-round the upper low packed an even bigger punch, producing strong afternoon thunderstorms with very high rain rates that resulted in severe flash flooding and debris flows in northern Los Angeles County and southern Kern County.

CIMSS Morphed Integrated Microwave Total Precipitable Water Imagery from October 12 shows the upper low entraining moisture from the sub-tropics and tropics as it retrograded into the Eastern Pacific.

Below are some NEXRAD Level-III/Google Earth composites of northern Los Angeles County and southern Kern County for the afternoon of October 15:

Overview

- PPS Storm Total Precipitation for the period ending 6:00 pm PDT. (KSOX)
- QPE Storm Total Precipitation for the period ending 6:00 pm PDT. (KSOX)
- PPS Storm Total Precipitation for the period ending 6:00 pm PDT. (KEYX)
- QPE Storm Total Precipitation for the period ending 6:00 pm PDT. (KEYX)

Lake Hughes - Elizabeth Lake Area

- One Hour Precipitation ending 3:30 pm PDT. (KSOX)
- Instantaneous Precipitation Rate at 3:20 pm PDT. (KSOX)
- Instantaneous Precipitation Rate at 3:30 pm PDT. (KSOX)

Leona Valley

- One Hour Precipitation ending 4:42 pm PDT. (KSOX)
- Instantaneous Precipitation Rate at 4:25 pm PDT. (KSOX)

Hwy 58 - Cameron

- One Hour Precipitation ending 5:39 pm PDT. (KEYX)
- Instantaneous Precipitation Rate at 5:21 pm PDT. (KEYX)
- Instantaneous Precipitation Rate at 5:30 pm PDT. (KEYX)

Here are NWS tabulations of some rainfall totals around the area for October 15 and some totals for October 16.

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

Thursday, 22 October 2015 08:54:24 (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Wednesday, 14 October 2015

UCAR NAM 12z Analysis for October 14, 2015 at 5:00 am PDT Click
UCAR NAM 12z Analysis 10/14/15
Click for Animation of Retrograding Upper Low

Recall that storm a week ago Monday that blasted down the West Coast and into the Southland? The Los Angeles County mountains received as much as two inches of rain; Downtown Los Angeles (USC) recorded 0.45 inch of rain; and the Sierra got a good shot of snow. (Here are some precipitation totals for that storm from the NWS Los Angeles/Oxnard and the NWS San Diego.)

Well, surprise, surprise that upper low isn't done with us yet! After a multi-day circuit into Arizona, Mexico and the Eastern Pacific, the low is now sitting off the coast of Southern California and forecast to move over the area on Thursday. The result is a chance of showers and thunderstorms today, Thursday and possibly Friday, particularly in the mountains. We'll see!

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

 

Wednesday, 14 October 2015 10:48:13 (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  |   |