Bay Area Rain: If You Blinked, You Missed It
I saw some evidence of precipitation, right here in the Bay Area, this morning about 6:30. The pavement outside my home in Berkeley was dappled by raindrops. But by 7 a.m., that moisture had evaporated and everything was dry again. My eyeball view of the weather — rain? what rain? — seems to be confirmed by weather reports, too. The National Weather Service’s hourly report on regional rainfall shows next to nothing in the way of precipitation: one-hundredth of an inch in Concord is the big dousing of the morning so far. The airports in Oakland and San Francisco have reported a trace of rain — the same as I saw in Berkeley. The Community Collaborative Rain, Hail and Snow Network (CoCoRaHS), an unofficial reporting system of volunteer weather observers, shows a handful of reports of .01 and .02 around the Bay Area.
So, 2013 moves on, the driest calendar year so far for San Francisco (and probably the rest of the region) since 1849, the year weather record-keeping started in the city. Here’s how the San Francisco Chronicle’s Peter Fimrite sums up where we are as of this week:
No rain at all fell in San Francisco in October and only 3.95 inches has fallen since Jan. 1, the smallest amount of precipitation to date since record keeping began 164 years ago, according to the National Weather Service….
… “It’s absolutely dry,” said Bob Benjamin, a National Weather Service forecaster. “We just went through October where there was no measurable precipitation in downtown San Francisco. That’s only happened seven times since records started.”
The previous record dry year was in 1976, when 5.57 inches of rain fell in San Francisco over the 311 days between Jan. 1 and Nov. 7. Meteorologists use San Francisco as a benchmark because it has the longest consecutive rainfall record in the state, going back to 1849-50.
The Bay Area’s bone-dry conditions have some water managers preparing to resort to “cloud-seeding” in order to sprout more precipitation. KQED’s Mina Kim spoke on Tuesday with Jeffrey Tilley, director of weather modification at the Desert Research Institute in Reno, Nevada.
Of course, not all is lost for the coming rain year. We’re at the very beginning of the rainy season, and as forecaster and local precipitation historian Jan Null points out, two of San Francisco’s wettest winters followed completely dry Octobers.
But for now, there’s worse to come. The National Weather Service’s Bay Area office in Monterey warns in its current forecast discussion that today’s non-rain event is likely to be followed by warm, dry, windy conditions:
MAIN FORECAST CONCERN FOR THE WEEK NOW APPEARS TO BE FIRE WEATHER
AS A MODERATE NORTHERLY SURFACE GRADIENT WILL COINCIDE WITH A
NORTH TO NORTHWEST FLOW ALOFT PLUS A SHORTWAVE TROF ROTATING
THROUGH SOME TIME ON FRIDAY. NAM 850 MB SPEEDS ARE EXPECTED TO
EXCEED 40 KT, SO WE COULD EASILY BE LOOKING AT LOCALLY GUSTY
WINDS, VERY LOW HUMIDITY VALUES, AND VERY DRY CONDITIONS WHICH
WOULD ALL COMBINE TO PRODUCE ELEVATED FIRE WEATHER CONCERNS. WE
COULD EASILY BE LOOKING AT WIND SPEEDS OF 20 TO 30 MPH OVER THE
NORTH AND EAST BAY HILLS WITH GUSTS IN EXCESS OF 40 MPH. WOULD NOT
BE SURPRISED IF A FIRE WEATHER WATCH AND THEN RED FLAG WARNING IS
ISSUED FOR THE EVENT AS IT GETS CLOSER. THE WINDS MAY CONTINUE INTO AT
LEAST PART OF SATURDAY.
NEXT WEEK IS ALSO SHAPING UP TO BE DRY AS THE RIDGE OUT OVER THE
PACIFIC IS EXPECTED TO EFFECTIVELY BLOCK ANY SYSTEMS FROM NEARING
OUR COAST. GFS ENSEMBLE MEMBERS INDICATE ONLY AROUND A 10% CHANCE
OF MEASURABLE DURING ANY GIVEN PERIOD, AND WITH THE ECMWF AND GEM
PORTRAYING SIMILAR DRY SOLUTIONS, KEPT POPS AND ANY MENTION OF
WEATHER OUT OF THE GRIDS.