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California Drought Situation Improves

By: Christopher C. Burt, 8:00 PM GMT on December 08, 2014

California Drought Situation Improves

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

Extreme Weather Drought

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

The recent and imminent precipitation is welcome and thanks for including appropriate caveats, Christopher. It's not time to breathe a sigh of relief yet.

California needs more rain, any way you count it - LA Times
State water resources officials said this week that it would take 150% of the average rainfall for California to recover from the current drought. The DWR measures rainfall at eight stations in the northern Sierra because water from those areas feeds the State Water Project.
An average of 50 inches of rain fell at those stations annually between 1922 and 1998. Using that average, officials said 75 inches of rain would need to fall in those Northern California spots by the end of the year to end the drought.

Since Oct. 1, only about 11 inches of rain has fallen at those eight stations.
NOAA does its measurements by calculating rainfall across the state — both in areas where it rains a lot and places where it rains relatively little. Federal scientists say 18 to 21 inches of rain is needed to end the drought for all of Northern California and coastal Southern California. It would take only 6 to 9 inches of rain to end the drought in inland and desert sections of Southern California, which typically get less rain.

To determine the level of the drought, NOAA uses models that rely mostly on the moisture levels of soil.
Trying to find specific time period as to when El Niño builds up the most.

Lets say the present period of rainfall lasts for 9-14 days and it gets "quite" again, spotty showers instead of a pineapple express. 

Which 3 consecutive months is it where El Niño builds up its most "stored energy"?, in other words the ocean is at its highest El Niño phase waiting for the rest of the biospheres (many just think its atmosphere & ocean) to connect. i thought it was May-Jul?, then all connects around Octt-Dec.

Just wondering in case this present flow lasts 9-14 days when will it be possible to see another build up of the ENSO area, therefore a chance for something stronger than a moderate El Niño? NOT SAYING monster kid as i read earlier in 2014 but just doing my own equations and am trying to pinpoint for myself the odds of 2 moderate El Niños** back2back over the next 5 yrs.

**(be they only Moderate or have a Modoki twist, that's not a drink)
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This is great news. BTW, I cannot remember (going back to the mid-1970s) the Mountain View site ever having the most rainfall among the official sites in the Bay Area for a storm. That must have been a very unusual alignment of the front and winds to bring that about. Mountain View is often the driest site in the Bay Area, along with Salinas. This would be like Palm Springs receiving the most rain in SoCal from a winter storm. So far, this winter is reminding me a lot of 1981-1982.
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