The Culprit Behind The Drought

The Culprit Behind The Drought

Stubborn High Pressure Serves as Record-Setting California Storm Blockade

Some scientists and politicians may try to lay blame for California’s drought on climate change but meteorologists have long known exactly what is most responsible for the West’s periodic dry periods.
High atmospheric pressure has been blanketing California and serving as a frustratingly effective storm and precipitation blockade for much of the past three years. This year’s “permanent” ridge of high pressure just happens to be much larger and far more stubbornly entrenched than those that occur routinely in most winters.


How big is it? National Weather Service meteorologists have described the high pressure ridge as being four miles high and, at times, some 2,000 miles long, acting like a wall in bouncing Pacific storms toward Oregon, Washington, British Columbia and Alaska. That immense region has been drenched by rain and coated thickly with mountain snow while California has been mostly warm and dry.
The ridge has broken down briefly only a few times, and for very short periods, since December 2012, most recently as February came to an end. With the storm door opened, welcomed storms began spreading much-needed wetness across California February 26.
A forecaster with the National Weather Service in Monterey told the San Jose Mercury News that the high pressure ridge has been “like the Sierra – a mountain range just sitting off the West Coast – only bigger. This ridge is sort of a mountain in the atmosphere. In most years, it comes and goes. This year it came and didn’t go.”
Conditions were much the same during virtually all of 2013, a year which many valley communities and other California cities recorded all-time record low calendar-year precipitation totals. Arid Bakersfield actually had more 2013 rain than normally damp San Francisco.


How the rest of the current winter and spring will play out remains to be seen but until the late February storms snuck through, the pesky high-pressure ridge had proven to be tougher and more persistent than one that created the 1976-77 drought. That water year was the San Joaquin River’s driest on record going into 2013-14.
High pressure systems are usually associated with fair weather but, like everything in the atmosphere and weather, there are numerous complexities constantly at work, many involving temperature.
There has been some speculation that the current drought may be a product of climate change but most scientists say they don’t know. “I wish I had a really good answer for this,” Daniel Cayan, an oceanographer and atmospheric scientist with the Scripps Institution of Oceanography in La Jolla, was quoted as saying in a news account. “It’s unusual for the pattern to have not broken down to allow some relatively active, vigorous winter storm systems to track across California.”
However, most water that ends up in the state’s vital system of reservoirs each year is captured from the work of what is usually just a few such potent storms. Without enough runoff, there is simply not enough water to store and create a significant supply.


There is growing hope among meteorologists that conditions may improve when the 2014-15 water year begins in October. Sea surface temperatures in the tropical Pacific are showing signs of possible development of an El Niño weather pattern beginning during the summer and continuing into the fall. In such a pattern, warmer than average sea surface temperatures often (but do not always) result in heavier than normal precipitation in much of California, a change that would be welcomed after three consecutive drought years.