Since the beginning of October, precipitation has been above normal from about the northern third of California and across much of the Northwest. Farther south, despite it feeling like it's been wet, a large percentage of Southern California and all the Southwest are either below, to much below normal for the season to date.
The all-important snowfall in the California Sierra has been pretty good. On average, the amount of water in the snowpack is pretty close to normal.
What lays ahead through the weekend is more stormy weather. A huge low sitting west of Washington and Oregon will be sending in waves of precipitation. The heaviest is mostly likely to be from southern Oregon into northern and central California. By the time the last of these storms moves through, there is going to be many feet of snow for the northern third of the Sierra through the Klamath and Siskiyou mountains and Shasta area. Between 4 and 6 feet seems likely over this time, including the ski resorts around Tahoe, while 5 to 10 inches of rain can fall in parts of the the North Bay and North Bay Mountains to northwest California and cause some flooding problems.
Rain and snow amounts decrease as one goes south in California. Only a little rain will reach into parts of Southern California Saturday night, but the trailing storm Sunday night into Monday will be stronger and bring a half of to one inch of rain and decent snow accumulation at Southern California ski areas. However, this storm will weaken as it moves into Arizona on Monday with perhaps no rain in the deserts and only light rain and snow in the mountains.
The outlook for Christmas Day is a little muddled by differences in timing of another storm. In general, the European is slower and preferred which would mean that rain could wait to arrive in the coastal Northwest until late in the day and it would be dry in all of California and the Southwest.
The amount of water in the snowpack in the Sierra is far below normal for even this time of year.
Flooding will be a given, most widespread in the northern half of the state.
This storm will endanger life and property both on the seas and over land in a large area.
A huge storm is expected it impact much of the Bering Sea beginning Friday night
This will be the first significant statewide rain and snow event of the season.