A very wet week from November 29th through December 6th brought widespread heavy rainfall to almost the entire state of California and has greatly improved the dire drought situation. With another big storm on the horizon there is hope that the worst of the long drought in California may at last be coming to an end.
The hills of California have turned green again for the first time in almost nine months following a five day period of heavy rainfall November 29th through December 3rd. The San Francisco Bay Area was especially hard hit with 12.12” of precipitation measured in Fairfax, Marin County and 11.62” in Tilden Park in the hills above Berkeley. However, all of the state saw a good soaking as the table below illustrates:
Table assembled by Jan Null of Golden Gate Weather Services with data from official NWS sources.
As a result of the storm(s) most of California is now running a seasonal precipitation surplus, the first time they’ve seen such since December 2012.
Precipitation for the water season that began July 1st and as of December 7th for selected California cities arranged geographically from north to south.
This map shows the percentage of normal precipitation for the hydrological water year that began on October 1st (vs. the seasonal water year that began July 1st in the table above) as of December 7th. Map from California Department of Water Resources.
At this point, the most significant impact of the rainfall has been to drastically improve soil moisture levels. The reservoir situation has also improved, albeit not so markedly. The state’s largest reservoir, Shasta Reservoir, has grown by 2% in volume and Lake Oroville, the 2nd largest and where most of the state’s drinking and urban use water comes from, saw an increase of 5% in volume as a result of the recent rain. Of course, overall, the reservoirs are still at near record low levels for this time of the year running at about 56% of normal capacity statewide for this time of the year
Reservoir capacities as of December 7th compared to their historical average for this time of the year. Map graphic courtesy of California Department of Water Resources.
The only disappointment has been the snowfall totals in the Sierra Nevada. The storms have been very warm and the snow levels consequently very high, generally above the 7,000-8,000’-foot level. In fact, the first week of December has been one of the warmest on record for much of the state with the average temperature running around 10°F above normal. Daily record highs have been observed in Oakland for the past three days, even topping out at 74° on Tuesday December 8th. Part of the reason for the abnormal warmth has been the near-record sea-surface temperatures along the Californian Pacific Coastline: ranging in general between 59°-63°F, at least 5°F above average and close to, if not actually, in record territory for early December.
Another reason for optimism is that the large-scale weather pattern seems have changed relative to that seen in the past couple of seasons. The PDO (Pacific Decadal Oscillation) is turning positive and a weak El Nino is trying to form. Although these changes are not any guarantee that the winter will continue to be a wet, they are, at least, a good sign. The RRR (‘Ridiculously Resilient Ridge’) that has been the hallmark of the drought these past few years is nowhere in sight (for the time being). Of course, this is the way the season of 2012-2013 began when a very wet November and December came to an abrupt end by January 2013 when the RRR set up and didn’t budge for over a year. Hopefully, this season will be different.
In the short term, however, things are looking good with a potentially powerful storm forecast to strike central and northern California later this week on Wednesday-Friday (December 10-12). In fact, if the forecast verifies, it may be the strongest and wettest storm to hit the region since October 2009 when the last major ‘pineapple express’ soaked the state.
GFS precipitable water forecast for the storm of December 10-12, a classic atmospheric river stretching from the Hawaiian Islands to the California Coast, hence the nickname ‘pineapple express’. Thanks to Stu Ostro at The Weather Channel for this graphic.
The storm is also forecast to be colder than last week’s and thus bring much heavier snowfall to the Sierra. Unfortunately, it does not appear that the southern portion of California will be much affected, especially the southern San Joaquin Valley which is still running drier than normal and, of course, is one of the nation’s most important agricultural regions.
I will update the precipitation statistics and reservoir capacities next Saturday (December 13th) following the storm.
Christopher C. Burt
Weather Historian
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