Finally, that record-breaking high pressure ridge off the California coast is starting to give — at least enough to let about half an inch of rain fall on Santa Rosa this week.
And it could be that February brings about 4 inches, which would be eight times wetter than January but nowhere near enough to offset a drought that dates back more than a year.
It would take more than 17 inches of rain by the end of February to get Santa Rosa back to normal, said Ken Clark, an Accuweather meteorologist.
“We've had miracles before,” Clark said, but he's not ready to bet on one this year.
The culprit is the high pressure system, shunting storms north into Alaska and British Columbia for the past 13 months.
Daniel Swain, a Stanford University weather analyst who posts the California Weather Blog online, dubbed it the “Ridiculously Resilient Ridge,” owing to its persistence — except for a brief summer break — since December, 2012.
Big ridges over the North Pacific occasionally form during winter, typically associated with warm, dry weather spells in California, Swain said in an e-mail.
The duration of the current ridge is “not something we've observed since at least 1948, which is as far back as the records go,” he said.
Its tenure is associated with all-time low precipitation records set recently throughout California, with most records going back more than a century, said Swain, a graduate student in Stanford's Climate and Earth System Dynamics Group.
Only now is the ridge breaking down, allowing a bit of a storm door to open, Clark said. Swain's blog called it a “temporary weakening” in the ridge.
Santa Rosa will get 0.3 to 0.6 inches of rain Wednesday night and Thursday, Clark said.
Accuweather is also forecasting five straight days of rain from Feb. 7 to 11, totalling 2 inches, and another 1.9 inches in the second half of the month.
“This is not a drought-buster,” Clark said, adding that long-range forecasts are always iffy.
What happens next isn't clear, Swain's blog said, noting that atmospheric models suggesting change in the ridge “have been wrong in every instance.”
Most likely, he said in Monday's e-mail, the ridge will rebuild over this weekend and resume blocking California's rain.
“The (ridge) has been incredibly stubborn now for two consecutive winters and there are not yet any convincing signs of its permanent demise,” he said.
Seasonal models forecast below normal rain through April, Clark said.
You can reach Staff Writer Guy Kovner at 521-5457 or email@example.com.