# Tuesday, July 28, 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, July 28, 2015 8:07:55 AM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   | 
# Monday, July 06, 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, July 06, 2015 10:56:10 AM (Pacific Daylight Time, UTC-07:00)  #    Disclaimer  |   |