Last Monday (Dec.8th) I posted a blog discussing the effect the California statewide rains of November 30-December 2nd had on the drought situation. As forecast, a major winter storm struck the state again this past week on Wednesday-Friday, December 10-12. The storm was the most powerful in at least two years to hit the state. Once again, another small step has been made so far as relieving the drought situation. Here is the latest update on the situation.
The second big round of storms pummeled California this week bringing monthly and seasonal precipitation totals to well above normal almost statewide. Map graphics from NWS-Sacramento.
The much anticipated big storm that hit California on December 10-12 lived up to its expectations with torrential rains, heavy snow in the Sierra, and high winds (although these were not as powerful as forecast). A small tornado (EF-0) even touched down in South Los Angeles Friday morning, December 12th. Rainfall in the San Francisco Bay Area was especially impressive with San Jose picking up 3.23” on December 11th, its 3rd greatest calendar day rainfall on record (POR since 1893). Venado, in Sonoma County, received 9.44” in 24 hours. What was most welcome, however, was that the heavy rain also drenched the southern portions of California including the Central Valley, erasing the seasonal precipitation deficits that were still in place just a week ago. Here is the difference the storm made (seasonal precipitation-wise) for selected cities across the state:
Precipitation for the water season that began July 1st and as of December 7th (top table) and as of December 12th (bottom table) for cities arranged geographically from north to south.
Maps 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) as of December 7th (top map) and December 12th (bottom map) . Map from California Department of Water Resources.
Reservoirs also benefited (although the run off is not yet complete). In the last week, the state’s largest reservoir, Shasta Reservoir, has grown by 5% 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 2% in volume. For the two-week period the capacities improved by 7% in both cases. Of course, statewide, the reservoirs are still at near record low levels at 58% of normal capacity for this date (an improvement of 2% over the past week and 4% over the past two weeks). See here for California Department of Water Resources latest reservoir capacities map/graphic.
Unlike, the storm(s) of November 30-December 2, the latest one brought significant snowfall to the Sierra Nevada and Cascade Ranges with a big improvement seen especially in the northern sector. After a warm start on Thursday, with snow levels at 8,000’ or higher, cold air behind the storm front lowered the snow levels to around 5,000’ on Friday, resulting in heavy accumulations at lower elevations and ski resorts. Here is the difference just one day made:
Snow/water content as a percentage of normal for this time of the year as of Thursday (top map) and Friday (bottom map). Still a long way to go to but a good start. Graphic courtesy of the California Department of Water Resources.
As I mentioned in my blog on December 8th: Another reason for optimism is that the large-scale weather pattern seems to be starting of the winter in a very different way tan seen in the past couple of seasons. The PDO is turning positive and a weak El Nino is trying to form. Although neither of these changes are any guarantee that the winter will continue to be a wet one, they are at least a good sign. The RRR (‘Ridiculously Resilient Ridge’) that has been the hallmark of drought 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 end by January when the RRR set up and didn’t let go for the following two years. Hopefully, this season will be different.
Things are still looking good in the short term as a series of (weaker) storms are expected on December 14-15, 16-17, and again on December 19-20. Each of these is forecast to be progressively colder, and thus add to the all-important Sierra snow pack.
Christopher C. Burt
Weather Historian
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