San Francisco has received zero inches of measurable precipitation this month, according to the National Weather Service. Barring a sudden Saturday downpour, this will be the city’s first rainless January since records began in 1850.
In average years, San Francisco will receive almost 4.5 inches of precipitation, and January has traditionally been the peak of the Northern California wet season. Yet despite a series of December showers, the Golden State remains locked in an ongoing drought.
Last year, California received less than 60 percent of its normal precipitation, though 2014 – both the hottest year in recorded history and the hottest in California history – still only ranks as the state’s third driest overall (the top spot belongs to 2013).
Changes in the global climate have led to record droughts and heat waves across the planet (see: Brazil, Australia, China and Europe), and California is no different. The state has been locked into four years of low rainfall and dry conditions largely due to a region of high atmospheric pressure known as a “blocking ridge.” Its stubborn permanence has led Stanford University’s Daniel Swain to call it the “Ridiculously Resilient Ridge.”
This ridge extends from the subtropical Pacific into northern Alaska and diverts the high-speed air currents that would normally bring rain and snow to the west coast. Both are necessary to replenish California’s water reserves and, because of the RRR, the Sierra snowpack is now at 25 percent its normal level. The liquid water stored in the Mammoth Pass is 20 inches below normal.
San Francisco did receive a cumulative 10.66 inches of rain in December, which is about six inches above normal, but that appears to have been a hiccup in an otherwise dry month. According to the U.S. Drought Monitor, most of California remains in extreme or exceptional drought conditions. Los Angeles has received just 1.21 inches so far; San Jose has received 0.02 in; and Sacramento, which typically averages 3.73 in of precipitation in January, has received a grand total of 0.01 inches.
The previous record for San Francisco’s lowest rainfall is 0.06 in, which was set last year.