Rain strain; Drought culprit is 'Ridiculously Resilient Ridge'

Unseasonably warm weather is predicted through Friday, with temperatures expected to reach as high as 68 degrees in McKinleyville today.

"The reason for this heat is the ridge of high pressure above us is causing winds in the east," said Shawn Palmquist, a meteorologist with the National Weather Service in Eureka. "As this wind comes out of coastal mountains, it becomes dry and warm air as it moves down the coast."

The normal mid-January temperature for coastal Humboldt County is 56 degrees.

While the weather term "polar vortex" ruled last week, California meteorologists ended up using "high pressure" extensively throughout 2013 to explain the rain-strained fall and winter that left the state -- and the North Coast -- with the driest year on record.

So dry that the National Weather Service issued a "red-flag warning" for fire danger in portions of southern Mendocino and eastern Lake counties that runs through Thursday -- an anomaly in winter. Last week, vegetation fires broke out in Bridgeville and Snow Camp in what one official termed "unheard-of incidents at this time of year."

"At this point in January, we've only had 0.73 inches of rain when usually at this time in January we have had 2.9 inches. January is typically our wettest month," Palmquist said. "Looking to the middle of next week, it seems like the ridge will still be over us."

The culprit for the emerging drought is a vast zone of high pressure in the atmosphere off the West Coast, nearly 4 miles high and 2,000 miles long, so stubborn that one researcher has dubbed it the "Ridiculously Resilient Ridge."

Like a brick wall, the mass of high pressure air has been blocking Pacific winter storms from coming ashore in California, deflecting them up into Alaska and British Columbia, even delivering rain and cold weather to the East Coast. Similar high-pressure zones pop up all the time during most winters, but they usually break down, allowing rain to get through to California.

This one, ominously, has anchored itself for 13 months, since December 2012, making it unprecedented in modern weather records and leaving researchers scratching their heads.

"It's like the Sierra -- a mountain range just sitting off the West Coast -- only bigger," said Bob Benjamin, a forecaster with the National Weather Service in Monterey. "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."

The current high-pressure ridge is even stronger and more persistent than a similar ridge that parked over the Pacific Ocean during the 1976-77 drought, one of the driest in the 20th century.

Scientists know that changes in temperature cause high- and low-pressure zones around the world. In many ways, air works like water. The deeper you swim in the ocean, the stronger the water pressure, because the weight of the water above is pressing down on the water below. Air in the atmosphere also has weight, and as temperatures of the ocean and land fluctuate, the atmospheric pressure also changes, helping drive much of our weather.

What researchers don't know, however, is why the current high-pressure ridge is so persistent, or when it is going away, allowing California to enjoy some much-needed rain. A few scientists say that it may be related to climate change, but nobody knows for sure.

"I wish I had a really good answer for this," said Daniel Cayan, an oceanographer and atmospheric scientist with the Scripps Institution of Oceanography in La Jolla. "It's unusual for the pattern to have not broken down to allow some relatively active, vigorous winter storm systems to track across California."

With each passing week, California's lack of rainfall becomes more serious.

Last year was the driest calendar year in recorded history for most cities in California, with records going back 160 years. The first snowpack reading in the Sierra Nevada earlier this month found a snowpack of just 20 percent of normal.

Since July 1, Eureka has received 5.85 inches of rain, or 29 percent of the normal 19.97 inches typically seen in the time period, according to the local National Weather Service.

State Department of Water Resources Director Mark Cowin told members of the California State Board of Food and Agriculture in Sacramento a week ago that his agency is likely to recommend that Gov. Jerry Brown declare a drought by Feb. 1, which would make it easier for water transfers between agencies and for emergency loans and other assistance.

All is not lost. Experts note that California still has another two or three months left in its winter season.

Meanwhile, Humboldt County farmers and ranchers are preparing for the worst.

"If we do manage to get a few decent storms, we could definitely get enough water to stave off the worst consequences of a really extreme water shortage," said Daniel Swain, a Ph.D. candidate at Stanford University in the Department of Environmental Earth System Science who coined the term "Ridiculously Resilient Ridge" on his blog, weatherwest.com. "But if we don't, we've essentially lost the whole water year."

Staff writer Jillian Singh can be reached at 441-0509 or jsingh@times-standard.com