California's (and LA's) record dry spell: where did the storm track go?

weather-records-2013.jpg
National Weather Service chart of low-rainfall records set in the Los Angeles area in 2013. Click to read bigger.

Two things to know up front. For the year, 2013 was the driest calendar year on record in California and in Los Angeles — the records go back to 1877. And when the state's hydrologists went up to measure the Sierra snowpack today, they found "more bare ground than snow." What snow they found totaled 20 percent of normal for this time of year. The first January survey in 2012 also found this level of snowpack — so that makes it seem common, right? Nope: those two years are the lightest January snow pack ever measured in the Sierra, the state Department of Water Resources says today. And this:

In addition to the sparse snowpack, many areas of California ended calendar year 2013 with the lowest rainfall amounts on record. Normally one of California’s wettest spots with an average annual rainfall of nearly 100 inches, Gasquet Ranger Station in Del Norte County ended the year with only 43.46 inches. Sacramento, which normally gets about 18 inches, ended up with 5.74 inches of precipitation. And downtown Los Angeles, which since 1906 has averaged 14.74 inches of rain, ended the year with 3.4 inches, beating the previous low of 4.08 inches recorded in 1953....


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DWR weather watchers note that it’s early in the season and this winter could still turn out wet. The concern, however, is that irrigation-dependent San Joaquin Valley farms and some other areas will be hard hit if we have another dry year without the cushion of reservoir storage that we had in calendar year 2013 due to the storms in late 2012 before California began sliding toward drought.

Lake Oroville in Butte County, the State Water Project’s (SWP) principal reservoir, today is at only 36 percent of its 3.5 million acre-foot capacity (57 percent of its historical average for the date). Shasta Lake north of Redding, California’s and the federal Central Valley Project’s (CVP) largest reservoir, is at 37 percent of its 4.5 million acre- foot capacity (57 percent of average for the date). San Luis Reservoir, a critical south-of-Delta reservoir for both the SWP and CVP, is a mere 30 percent of its 2 million acre-foot capacity (43 percent of average for the date) due both to dry weather and Delta pumping restrictions last winter to protect salmon and Delta smelt. Delta water is pumped into the off-stream reservoir in winter and early spring for summer use in the Bay Area, San Joaquin Valley, Central Coast and Southern California.

Some news coverage before today's stats were released: KCRA, Contra Costa Times, U-T San Diego

Also this. The California Weather Blog analyzed the weather condition that is keeping the usual flow of winter moisture from reaching California, and compares the current dry period to the 1976-77 drought that forced changes in the state. First, a lesson about the "Ridiculously Resilient Ridge of 2013," as the blog calls it.

Zonal (west-to-east) flow typically predominates during the cool season in this region, which directs storm systems that develop over the ocean toward the West Coast. While the storm track does often vary in latitude along the West Coast over the course of any given winter, southward excursions of the jet stream usually bring periods of significant precipitation to much or all of California...2013, however, has featured rather incredibly persistent atmospheric anomalies over the northeastern Pacific Ocean and the West Coast of North America. The typical zonal flow over the Pacific has been much weaker than average and displaced well to the north, occasionally as far north as continental Alaska. This means that the storm track has largely missed the West Coast entirely...


The proximate cause of this highly anomalous high-latitude storm track over the Pacific–as I have discussed in previous posts–is the Ridiculously Resilient Ridge of 2013 (or the RRR, for brevity). ...This persistent ridging has resulted in a flow pattern that has deflected existing Pacific storms well to the north of California and suppressed the development of other systems closer to the state. Persistent ridges that disrupt the prevailing westerly winds in the middle latitudes are often referred to as “blocking ridges” because of their propensity to impede and deflect typical atmospheric flow patterns, and the RRR is no exception.

Because this blocking ridge and its associated poleward (south-to-north) wind anomalies are centered well offshore, California has generally been in the equatorward (north-to-south) wind anomaly region and thus an unusual amount of our weather events over the past year have originated to our north or even northeast over western Canada. These dry and windy “inside slider” disturbances, so named for their over-land trajectory to the east of the more typical coastal route, have been responsible for the numerous offshore flow events that have contributed to record high winter fire danger in northern and central California.

OK, other than that, things are good, right? The current dry season is different from the last time California really suffered from severe drought, in 1976-77. That was two record bad years back to back. The current situation is a record bad year following a so-so year. So we're a bit better off, and that's at least something:

The 1976-1977 drought is notable for two reasons: the objective meteorological magnitude of the event in terms of the enormous precipitation deficit and also the enormous (and in many cases permanent) effect it had on human systems in California. The mid-70s drought garnered substantial media attention due to the regionally exceptional water shortages that it caused, with impacts ranging from the temporary cessation of agricultural activities in some parts of the Central Valley to the construction of an emergency water pipeline across the Richmond-San Rafael bridge in the Bay Area when local reservoirs ran almost completely dry. This drought event led to significant changes in water management practices in the state of California, including the development of more aggressive contingency plans for relatively short-term (1-2 year) periods with extremely low precipitation.


Another angle:

At Folsom Lake east of Sacramento, the foundations of a Gold Rush Mormon settlement that were submerged under the reservoir in 1955 are visible again. KCRA-TV paid a visit.

Similar at Lake Cachuma in Santa Barbara County. Noozhawk


More by Kevin Roderick:
Friday news briefs and desk clearing
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