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La Nina/State Weather & Climate update

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La Nina/State Weather & Climate update

Postby gdurkee » Sun Dec 16, 2007 5:13 pm

Advertised storm potential for next week is still in play. A pattern shift will send a series of storms to the west coast next week. If a split flow regime does not set up, and if the models aren't projecting too south a track, the Northern Sierra should be in for at least two, possibly three systems between Monday and Thursday of next week. These will be productive, and fairly cool. The snow level will be around 5,000' with these, and each has a one to two inch precipitation potential. At this time, it looks like 3 to 4" total by Friday night 12/21.

Southern California fared well last week, with flood concerns over the burn areas. In spite of another 1/2" to 2" of rain in some places, no mudslides were reported. The next round of weather systems will impact Northern California moreso than southern. But at least one of the fronts will likely bring rain that far south.

Numbers have a boost from last week: 8 Station precipitation for the season as of December 10, 2007 stands at 7.1", or 14% of an average season, 59% to date. October had 3.5", or 117% of average, November 1.1", or 17% of average, December is at 2.5", or 30% of average December to date).

>From our Snow Surveys section;

The December Water Supply Index (WSI) has been issued for conditions through December 1, 2007 for the Sacramento and San Joaquin Valleys. The Sacramento River Runoff forecast is 13.8 MAF (74% of average). The median Water Year Type index for the Sacramento Valley is "Dry". The Water Year Type index for the San Joaquin Valley is "Critical" (based on the 75% exceedence forecast). Those are the same designations that last water year ended on.

The WSI is posted at:

Since October 1, precipitation was 50% of average in the Sacramento River region, 39% of average in the San Joaquin River region, and 29% of average in the Tulare Lake Region. November unimpaired runoff in the Sacramento River Region was 42% of average. Cumulative Sacramento River Region runoff since October 1 is about 60% of average compared to about 76% a year ago. November unimpaired runoff in the San Joaquin River Region was about 15% of average. Cumulative San Joaquin River runoff since October 1 is about 26% of average compared to 56% a year ago.

The next Water Supply Index for conditions through January 1, 2008 should be available on or around January 8, 2008. The first Statewide snow survey measurements of the water year will be conducted on Thursday, January 3rd, 2008. Results from the surveys will be available shortly thereafter.

The latest La Niña update from the Climate Prediction Center is that a moderate-strength La Niña is present across the tropical Pacific Ocean, and that recent equatorial Pacific sea surface temperature trends and model forecasts indicate La Niña will continue into Spring of 2008. For more on the long range climate forecast, go to: ... enso.shtml

The latest U.S. Seasonal Drought Outlook valid through February, 2008 places the southern half of California in the "Drought ongoing, some improvement" category. From the Bay Area across the Sacramento/ Marysville area, and on up through the Feather Basin and far northeastern California, conditions are labeled, "Drought likely to improve, impacts ease."

Here is the website for Water Plan 2009. You can sign up for a weekly email update.

Another newsletter will go out next week some time.


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