California: What a Difference a Month Makes

Published: 21:58 GMT le 08 janvier 2016

California: What a Difference a Month Makes

One month ago I posted a blog about the precipitation deficits that were endemic in California at that time (December 9, 2015) but just prior to the beginning of a series of storms that rolled in. As was expected, the storm door opened and remains open. Here is where California now stands as of January 9th, 2016 precipitation-wise. Looking a lot better!

Precipitation Totals

Although there have been no major storms so far this season there has been a non-stop series of moderate storms affecting one portion of the state or other every few days since last December 10th. The northern and central portions of California were the main beneficiaries of these until this past week when southern California finally got into the act. Even more crucially, the Sierra has been plastered with heavy snowfall and, for the first time in several years, the water content of the snowpack is above normal for the season-to-date at this time (at least on an averaged state-wide basis). Below are some tables and graphics illustrating this.

The top table shows the rainy season-to-date precipitation amounts as they stood last December 9th and below that a table of where they stand now (as of January 7th) for selected sites across California arranged geographically from north to south. As one can see there has been a tremendous improvement at the central and northern sites whereas Los Angeles and San Diego are holding their own.

The final precipitation totals for the calendar year of 2015 (below) show how dry it has been in spite of the December rainfall. The entire state averaged well below normal and actually near-record dry for some locations, such as San Francisco which experienced its 4th driest calendar year on record since records began in 1849 with a 9.91” total (downtown). Its driest calendar year was just two years ago, 2013, when only 5.59” was measured.

Reservoirs and Snowpack Conditions

The runoff from the December rainfall has begun to finally replenish the state’s reservoirs. It will take a long time (probably not this year) to finally reach 100% of average. Below are a comparison of major reservoir levels as of December 8th and the situation now (January 7th). Note that the state’s largest two reservoirs (Shasta and Lake Oroville) have improved their percentage of historical average (for date) by 3% and 5% respectively. Folsom Lake has seen a huge improvement from 29% of normal capacity on December 8th to 53% now.

California state reservoir capacity levels as of December 8, 2015 (top) and January 8, 2016 (bottom). Apologies for the change in the map designs, it appears the CA Dept. of Water Resources has made a design change sometime this past month. Maps provided by the California Department of Water Resources.

Similar to the maps of the reservoirs are the maps comparing the snowpack water content as of December 8, 2015 and now (January 7). Overall, the percent of normal to date went from 59% on December 8th to 107% currently.

Snowpack water equivalents as percentage of normal as of December 8, 2015 (top map) and as of January 7, 2016 (bottom map). Again, the design of the maps has changed slightly over the past month. Maps provided by the California Department of Water Resources.

Here is how the snowpack water content this season (so far) compares with last season as well as comparisons to the driest and wettest seasons on record:

The purple line is where we stand now for each of the Sierra regions (north, central, and south). Last season (2014-2015) ended up tied or a little drier than the previous driest season on record of 1976-1977. Graph provided by California Department of Water Resources.

The hope, at this point, is that the storms will continue to roll in on a regular basis for the rest of the winter and spring. With the El Nino still on track to be one of the strongest if not the strongest on record, there is a good chance this will happen despite a few dry spells from time to time.

Christopher C. Burt
Weather Historian

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About The Author
Christopher C. Burt is the author of 'Extreme Weather; A Guide and Record Book'. He studied meteorology at the Univ. of Wisconsin-Madison.

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