Above: From NASA's Worldview site, an image of California's first real storm of the wet season (click for a larger version, or check it out on Worldvew). Here's (a slightly edited version of) how the National Weather Service's San Francisco Bay Area forecast office described the weather system as it was shaping up early Sunday:
AS OF 09:59 AM PST SUNDAY...NORTH AND CENTRAL CALIFORNIA ARE CURRENTLY POSITIONED IN THE BOUNDARY BETWEEN TWO LARGE FEATURES. TO THE SOUTH...THE HIGH PRESSURE THAT HELPED TO BRING CLEAR SKIES AND UNSEASONABLY WARM TEMPERATURES OVER THE PREVIOUS FEW DAYS. TO THE NORTH...AN APPROACHING STORM SYSTEM WITH A POTENT MOISTURE TAP. A COLD FRONTAL BOUNDARY IS SEPARATING THESE TWO AIR MASSES AND IS EVIDENT ON BOTH RADAR AND SATELLITE FROM THE THICK BAND OF CLOUDS AND CONTINUOUS RAINFALL REFLECTIVITIES ASSOCIATED WITH IT. THIS FRONTAL BOUNDARY IS CURRENTLY DRAPED FROM NORTHWESTERN CALIFORNIA THROUGH SOUTHEASTERN OREGON AND HAS BROUGHT UP TO 2.5" OF RAIN ALONG THE HIGHER TERRAIN OF THE OREGON COAST AND UP TO 2" OVER THE HIGHER TERRAIN OF THE NORTHWESTERN CALIFORNIA COAST. THESE HIGHER VALUES ARE SUPPORTED BY A TROPICAL pMOISTURE PLUME WITH PRECIPITABLE WATER VALUES RANGING FROM 1.2"-1.6" WHICH ARE 150-200 PERCENT WETTER THAN NORMAL. LOWER ELEVATION LOCATIONS IN THESE AREAS HAVE NOT PICKED UP NEARLY AS MUCH... RANGING FROM SEVERAL HUNDREDTHS TO A FEW TENTHS. WE WILL LIKELY SEE SIMILAR ELEVATION BASED PRECIP SCALING FROM THE FRONT AS IT MOVES THROUGH OUR AREA THIS AFTERNOON AND INTO EARLY MONDAY.The rain started here in Berkeley about 9 p.m. or so. It's been more than a drizzle: .29 of an inch in the last couple of hours, on the off chance that the backyard rain gauge (which I got just after the last rain of the spring) is correct. That seems to line up with other rain gauges around town that report on Weather Underground. We'll see how accurate it looks tomorrow.