The RRR ‘Ridiculously Resilient Ridge’ Returns to California

Published: 10:04 PM GMT on January 09, 2015

The RRR ‘Ridiculously Resilient Ridge’ Returns to California

After a very wet first half of December hopes were high that the beginning to the end of California’s years-long drought might finally be at hand. However, virtually no rainfall has fallen across the state since December 18th and none is forecast until at least January 18th. Yet again, a month-long mid-winter dry spell has befallen the state.

Although mid-winter dry spells of two or three weeks are relatively common in California, it is rare that four or more dry weeks occur during the heart of the normally wettest time of the year December-March. During the wet season of 2012-2013 a rainy November and December (2012) came to an abrupt end by January (2013) and the drought began in earnest as a persistent high pressure ridge locked in place over the eastern Pacific (the so-called ‘Ridiculously Resilient Ridge’) and basically remained in place until February 2014. This resulted in the calendar year of 2013 becoming the driest year on record for California. During the wet season of 2013-2014 significant precipitation did not occur until February (2014) when the ridge finally broke down. In spite of the February 2014 rain and snow events, drought conditions worsened throughout the year until the heavy rains of this past December (2014) alleviated some aspects of the drought with state reservoirs gaining back around 5% of their capacities and soil moisture replenished temporarily.

This satellite comparison of ground conditions in California for January 2, 2014 and January 3, 2015 illustrates how the past wet December improved soil moisture conditions in the Central Valley and snow coverage in the Sierra. Graphic courtesy of Thomas Niziol of The Weather Channel.

Now, it appears, the RRR has settled in once again deflecting Pacific storms to the north of California (and bringing flooding to Washington State). No precipitation is on the horizon (going out to at least January 17-18) and some locations in the state have already fallen below seasonal normal precipitation for this time of the year, this following a well above normal wet December.

A comparison of seasonal precipitation totals and their percentages of normal as of December 12, 2014 (bottom table) and as of January 8, 2015 (top table) for select California cities. The list is arranged geographically from north to south across California. By the end of next week (around January 17th) the percentages will have slipped even more significantly if no precipitation falls as is currently forecast. The first half of January is historically one of the wettest two-week periods of the year.

The snow water content in the Sierra Nevada and Cascades is also very disappointing, given all the precipitation that fell in December. At least, so far, the situation is still much better than last year at this time.

Sierra Nevada snow/water content for the northern mountains (Sierra and Cascades), central Sierra, and southern Sierra zones. The blue line is this season (2014-2015) as of January 8th compared to the last two seasons and the historical extremes. As of January 8th the snow/water content for all the regions statewide is 40% of normal for this date. Data from the California Department of Water Resources.

The most recent California Drought Monitor map (conditions as of January 6, 2015) illustrates that 32% of the state is still in the ‘exceptional drought’ category and 78% in the ‘extreme drought’ category. However, we can see some improvement since last October when drought conditions peaked (58% experiencing ‘exceptional drought’ and 82% ‘extreme drought’). NOAA/NCDC.

Not Just Dry but Warm too

According to NOAA/NCDC, the calendar year 2014 was the warmest such on record for the state of California: by the HUGE margin of 1.8°F! The 61.5° statewide average temperature smashed the previous record of 59.7° set in 1934. December was also the warmest such on record for the state and the past few days, this January, have once again seen many daily record highs statewide. On January 6th, the temperature peaked at an amazing 91° at Camarillo in southern California (the January monthly state record remains 97° at Riverside in January 2003).

Average annual temperatures for California and the contiguous U.S. since 1895. Data from NOAA/NCDC.

NOTE: I will be taking a six-week leave of absence, so this will be my last post until around February 20th.

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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