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.

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.

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.

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.

A dynamic cutoff upper low centered over Southern California produced numerous thunderstorms in Southern California and a broad area of the southwestern U.S. Saturday. The thunderstorms produced thousands of lightning strikes, some heavy downpours, hail and strong winds.

According to an article on Yuba.net over 15,000 lightning strikes were recorded in California over the 24 hour period ending 0600 PDT Sunday. This plot of lightning detections was produced by Tahoe National Forest. (Typically lightning detections include both cloud-cloud and cloud-ground strokes.)

Thunderstorms were widespread in Southern California and several strong thunderstorms were reported by the NWS. This NWS NEXRAD image from about noon on Saturday shows several strong cells including one area flagged as severe. This composite image from WSI/Intellicast.com at 2:45 pm PDT shows estimated cloud tops, cell movement and hail. Half inch hail was reported in several locations by NWS spotters and there was one report of 1.25 inch hail near Lake Los Angeles. A wide swath of enhanced thunderstorm activity developed in the afternoon to the north and northeast of Los Angeles.

Some of the higher rainfall totals reported by the NWS include Lake Palmdale at 0.98 inch; Palmdale 0.84 inch and Lockwood Valley 0.58 inch. Downtown Los Angeles recorded a trace. Here's a NWS Los Angeles/Oxnard tabulation of some rainfall totals from around the area. Here also is a NWS San Joaquin Valley/Hanford tabulation of some rainfall totals in the southern San Joaquin Valley and Sierra.

In a Southern California Weathernotes post in February I commented that the tough question regarding La Niña was whether warming would continue into the NH summer, with neutral ENSO conditions prevailing as we move into autumn; or if the ENSO cycle would swing back toward a La Nina state. It was noted that since 1949, about half of the first year La Nina episodes have continued into a second or third year.

Climate scientist and Multivariate ENSO Index (MEI) codeveloper Klaus Wolter first mentioned the roughly 50/50 chance that La Nina would return following a summer respite in September 2010. A glance at a plot of the extended MEI index, going back to 1871 clearly shows a propensity for a return of La Nina in the year (or years) following stronger La Nina episodes.

In a September 8, 2011 press release NOAA reported that La Nina is back. More precisely, in their September 8 ENSO Diagnostic Discussion CPC states "La Niña conditions have returned and are expected to gradually strengthen and continue into the Northern Hemisphere winter 2011-12." The Multivariate ENSO Index (MEI) has dropped below the weak La Nina threshold, and several oceanic and atmospheric factors are indicative of a reemerging La Nina. There's still a (historically) slight chance of a return to ENSO neutral conditions this fall, but it doesn't appear likely. We'll see!

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

October was an unusually wet month in coastal Southern California. Many areas recorded more than an inch above normal rainfall, and some as much as 3 inches above normal. In a month where around 0.5 inch is considered normal, some areas received several times the normal amount of rainfall.

Most of October's rain resulted from two energetic upper lows, and a relatively strong trough/front that swept through the area October 30th. The front produced a new precipitation record for the date of 1.09 inches at Santa Barbara Airport Here's an archived NWS Public Information Statement with some rainfall totals for that storm.

Last week, an approaching Pacific trough pumped up a thick high pressure ridge over California, sending temperatures soaring and breaking temperature records across the area. November 3rd Long Beach Airport set a new high temperature record for the date of 100°F, and Downtown Los Angeles set a new record of 97°F. November 4th temps were once again in high 90s and several stations broke or tied high temperature records. Here are archived copies of the NWS Record Event reports for November 3 and November 4.

The southern part of the Pacific trough that produced our record high temps cut-off into a small upper low as it approached the coast, and moved onshore north of the Los Angeles basin on Saturday. The remainder of the trough and its associated front moved through the area Sunday evening into Monday. The front held together a little better than expected, and rainfall totals in the Los Angeles basin and valleys generally ranged from about 0.10 inch to 0.30 inch. Here's an archived NWS Public Information Statement with some rainfall totals from around the area..

The latest round of rainfall leaves many areas of Southern California way ahead on rainfall totals for the water year. Downtown Los Angeles (USC) missed out on a couple of the systems, and as of close of business yesterday has recorded 1.10 inch for the water year, which is only 0.06 inch above normal. By comparison, Los Angeles Airport is 0.85 inch above normal, and Camarillo/Oxnard is 0.97 inch above normal. This headstart on the rain season should help keep our rainfall totals a little closer to normal as our La Nina influenced rain season continues.

Speaking of La Nina, the September/October value of the Multivariate ENSO Index (MEI) increased slightly by 0.079 sigma, ending the record plunge from El Nino conditions earlier this year. In the past 30 days there was some decrease in the magnitude of negative SST anomalies in the east-central equatorial Pacific, but subsurface temperatures remain quite cool. Computer models are split on whether Nino 3.4 SST anomalies will continue to decline in magnitude during the Northern Hemisphere winter, but nearly all models indicate decreasing anomalies in early 2011. We'll see!

More information concerning Southern California weather can be found using our WEATHER LINKS page.