Updated January 10, 2008. The ESRL-PSD Composite ENSO plots page was updated today to correct an issue that resulted in the wrong set of years being used for its Winter La Nina composites. As a result the La Nina composite precipitation map in this post has been updated.

Grasses sprouting as a result of our record setting September rainstorm have brushed our sun parched hills, fields, and woodlands with pleasing hints of green. Whether these areas will remain green depends on how much rain we receive this Fall and Winter.

According to the Climate Prediction Center’s Weekly ENSO Update, issued October 1, La Niña conditions are present across the tropical Pacific and are likely to persist through early 2008. As a result, several longer range U.S. precipitation outlooks are similar to this Nov-Dec-Jan Precipitation Outlook, issued September 20 by the CPC.

The precipitation pattern projected for the western U.S. is typical of a La Niña, with an increased chance of higher than normal precipitation in the Pacific northwest and an increased chance of lower than normal precipitation in the southwest.

The September 20 CPC outlook indicates an “equal chance” of below normal, near normal, or above normal precipitation in the Los Angeles area. However, the La Niña has strengthened recently, so the next precipitation outlook may reflect a more pessimistic projection of Los Angeles area rainfall.

As mentioned above, the ESRL-PSD Composite ENSO plots page was updated today to correct an issue that resulted in the wrong set of years being used for its Winter La Nina composites. This updated precipitation map shows the mean Nov-Mar precipitation for the U.S. during 9 La Niña events from 1948 to the present. Note that the average La Niña rainfall indicated for coastal Southern California is in the 7.0-10.5 inch range, rather than the  10-15 inch range previously indicated in the ESRL-PSD graphic.

The two driest water years recorded in Los Angeles since 1877 have occurred in the last seven years. During the most recent, from Jul 2006 to June 2007, downtown Los Angeles (USC) measured only 3.21 inches of rain. In that context 10-15 inches sounds quite wet! We’ll see.

The photograph of new grass sprouting amid oaks is from a run at Sage Ranch on October 1, 2007.

Sporadic rain in the Los Angeles area has finally produced a little green in local open space areas. Here, along the margins of the “main drag” in Upper Las Virgenes Canyon Open Space Preserve (formerly Ahmanson Ranch).

As of today, (preliminary) NWS climate data indicates Downtown Los Angeles (USC) has recorded 1.92 inches of rain since July 1. This is 7.31 inches below normal. Leafing back through weather service data prior to July 1, this is the total rainfall recorded since May 22, 2006 – a period of nearly nine months.

What happened to our El Nino rains? According to NWS scientist Ed Berry, “the global circulation has been generally La-Nina like since about late November.” This is despite an El Nino event that peaked in November or December, and persisted at moderate strength into January. See his blog Atmospheric Insights for the technical details.

A period of unsettled – possibly showery – weather is forecast for the Los Angeles area beginning Sunday evening and continuing pretty much through the week. At the moment* the best chance for measurable rain appears to be on Monday and Thursday. We’ll see!

*Updated Saturday, February 17, at about 11:00 a.m.

Related posts: The Color of Rain, El Nino Drought, Sunset Snow Shower, Rainy Morning on Rocky Peak Road.

The open space areas in which I run would normally be lush and green by this time of year, particularly when there is an El Niño. But in the past 231 days (including today) the official weather station for Los Angeles has recorded only 1.31 inches of rain, and the hills remain a dank sun bleached gray-brown.

As mentioned in my post The Color of Rain, usually when there’s an El Niño, wet Winter weather can be expected to occur in Southern California. This year’s El Nino was late to develop, became stronger than expected, and may have already peaked.

Warm water in the tropical western Pacific contributes to the development of an El Niño, and studies show this pool of warm water has been increasing in temperature, perhaps increasing the strength and frequency of El Nino’s. The quirkiness of this year’s El Niño may be related to these changes.

Is any relief to our drought in sight? Not in the short term. A system forecast to affect the Los Angeles area Thursday and Friday will likely result in cooler temperatures and more wind, but little – if any – rain*.

In his blog Atmospheric Insights, NWS scientist Ed Berry discusses the possibility of a high impact precipitation event developing in California later this January*. A flow pattern with a strong lower latitude jet stream is typically associated with El Niño induced precipitation events in California.

California weather this rain season will be closely monitored by scientists participating in NOAA’s Hydrometeorological Testbed (HMT) Program. This program is “aimed at accelerating the infusion of new technologies, models, and scientific results from the research community into daily forecasting operations of the National Weather Service (NWS) and its River Forecast Centers (RFCs).”

The photograph of the dry grasslands in the Simi Hills west of Rocketdyne was taken on a run to the northern boundary of the Upper Las Virgenes Open Space Preserve on December 24, 2006. The photograph of the green hills in the Ahmanson Ranch area of the Upper Las Virgenes Open Space Preserve is from a run on January 18, 2005.

*Updated 01/10/07. Today’s runs of the computer weather models are projecting from about 0.1 inch to 0.25 inch of rain from this system at Los Angeles. Also, see the January 10 update to Ed Berry’s Atmospheric Insights blog. Consolidation of the Pacific jet now appears unlikely, so we may not see typical El Nino impacts developing in California this month. There may be rain, but perhaps not as a result of a classic El Nino pattern. We’ll see!