The persistent high pressure ridge...
California drought: What's causing it?
mercurynews.com
Posted: 01/13/2014 05:32:36 PM PST
As California struggles through a run of historically dry weather, most residents are looking at falling reservoir levels, dusty air and thirsty lawns.
But meteorologists have fixed their attention on the scientific phenomenon they say is to blame for the emerging drought: a vast zone of high pressure in the atmosphere off the West Coast, nearly four 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."
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