Rapid transition from record warmth & dryness to very wet pattern
From Daniel Swain at the California Weather Blog:
February was an extremely warm month (once again!) across the entire state of California, with a seemingly endless list of temperature records being broken on a daily basis. February was also quite a dry month across the state, with essentially the only precipitation event of any note occurring around the middle of the month. Sierra Nevada snowpack–which had been hovering slightly above average through the end of January–started to fall behind by mid-month, and March 1st snow survey showed statewide snowpack slightly above 80% of average for the date. This number is decidedly far better than during recent winters, but that’s really only a testament to the abysmal snowpack accumulations during the reign of the Ridiculously Resilient Ridge. A rather abrupt change in the prevailing weather pattern is now at California’s doorstep, however. The persistent ridging of the past month or so is rapidly being displaced by a series of powerful storm systems, driven by a remarkable enhancement and consolidation of the Pacific jet stream.