Marin County is now officially in abnormally dry conditions, but unlike much of the Bay Area it has not slipped into a moderate drought, according to the U.S. Drought Monitor.
The latest report — a weekly analysis by the National Oceanic and Atmospheric Administration, the U.S. Department of Agriculture and the University of Nebraska-Lincoln — places 48% of California in the moderate drought category, up from 34% a week ago.
The report, which monitors a range of indicators, places about 30% of California in the abnormally dry category, the least severe of five classifications. Marin was classified as normal as recently as four weeks ago.
The Marin Municipal Water District reported 27.88 inches of rain at Lake Lagunitas from July 1 through Tuesday. That is 32.45 inches less than last year and about 66% below average for the date.
There is some hope in the forecast, however. Cooler, wetter conditions are expected this weekend across the Bay Area. And a significant snow storm is heading toward the Sierra, where the National Weather Service has issued a winter storm watch from 11 a.m. Saturday until 11 a.m. Monday, with wind gusts of up to 60 mph. and snow levels down to 2,000 feet.
“There will be major delays, chain controls and likely road closures in the mountains due to white-out conditions,” said Idamis Del Valle, a meteorologist with the National Weather Service in Sacramento. “We’re not advising people to travel on Sunday.”
The storm is expected to dump 1 to 2 feet of new snow in the Lake Tahoe area this weekend, with 3 to 4 feet at higher elevations in the Sierra, like Sonora Pass, Ebbetts Pass and Carson Pass.
That would make it the biggest snow storm in California in three months, since Dec. 5, when roughly 3 feet fell in some Sierra locations.
Skiers heading to Lake Tahoe this weekend should leave Friday, and no later than early Saturday morning, she said. Getting back to the Bay Area will be difficult until Monday.
A persistent ridge of high pressure that has blocked storms all winter from hitting California is breaking down, at least for a while, allowing the weekend rain and snow to move in from the Gulf of Alaska.
While not as dramatic as the Sierra forecast, rain is expected to arrive in the Bay Area on Saturday, Sunday and Monday, forecasters say. Totals are expected to be modest, ranging from a quarter inch to three-quarters of an inch in most Bay Area cities, with up to 1.5 inches in the hills, ridges and peaks across the region. Colder temperatures also could bring some snow to the Bay Area’s highest peaks.
“Any precipitation postpones fire season,” said Jan Null, a meteorologist with Golden Gate Weather Services in Half Moon Bay. “I don’t think the amounts are going to move the needle much in terms of water supply impact. Soils are awful dry right now. Everything is soaking in.”
Luckily for California’s water supply, because of a wet winter last year and the year before, reservoirs across the state continue to hold a significant amount of water, which will help reduce the risk of shortages this year.
On Wednesday, Shasta Lake, the state’s largest reservoir, was 77% full — 102% of its historic average for late February. Lake Oroville was 64% full, or 88% of its historic average. And San Luis Reservoir near Los Banos was 69% full, or 79% of average for this time of year.
The unusually dry conditions, however, are generating concern that if dry conditions continue next winter, California may be heading toward another drought crisis, not unlike the five-year drought it experienced recently. And the dry winter this year likely means a summer with high fire danger.
The Sierra Nevada snowpack, the source of one-third of California’s water, on Wednesday was just 38% of its historical average — down from 92% on New Year’s Day.
“This storm could certainly bump up the numbers, but we’re still below average,” said Del Valle. “It’s been extremely dry.”
Cities across California are 5 to 10 inches under seasonal rainfall averages, a deficit that would require 15-20 more storms like the one expected this weekend to get back to normal.
Since Oct. 1, San Jose had received just 4.1 inches of rain through Wednesday night, or 34% of its historical average for that date. Oakland was at 36%, with 5.8 inches. And San Francisco was at 47% of normal, with 9 inches.
Light rain last Friday and Saturday snapped a 37-day winter dry spell in San Francisco, the fourth longest consecutive streak without winter rain in that city since the Gold Rush in 1850 when modern records first began. But only about two-tenths of an inch fell overall.
What about a “Miracle March” with late, drenching Pineapple Express storms that could bring rain totals back near normal? Not likely, if history is any guide.
San Francisco, a barometer for broader Bay Area weather trends because it has the longest set of weather records, has experienced 18 years since 1850 when February rain totals were unusually dry — below half an inch. And in those years, only six times did March end up with above-normal rainfall, according to a recent analysis by Null.
“I’ve heard people say we’ve had a dry February, so that means a wet March,” Null said. “But if you look at the numbers that’s not true. Two times out of three we end up below normal.”
The upcoming storms and some that are possible next week, if they come through, should bring about 1 to 1.5 inches to the Bay Area, Null said. That would bump San Jose and Oakland’s seasonal rainfall totals up to about 40% of normal, and San Francisco’s to about 50%. But these storms from Alaska aren’t the atmospheric river “Pineapple Express” variety that can quickly send rainfall totals soaring — and which are nowhere in the forecast.
“This is not the type of pattern we want,” he said. “We want something from the west with a lot of tropical moisture. That’s the key.”
