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After a late December and January to remember, the North Bay and Northern California are far above average in rainfall and snowpack. In fact, some state reservoirs are releasing water in order to make room for additional winter rainfall, and snowmelt this spring.
Let’s take a look at where we stand, then we’ll look at the outlook ahead.
First, Lake Sonoma, which supplies drinking and agricultural water to most of the North Bay has gone from just over 100K acre feet when the storm cycle began, to 227K acre feet as of January 15th. That is just 20K acre feet short of the full water supply pool of 245K acre feet, and approximately 109% of average for the date. (Image 1) (The total capacity figure in red indicates the FLOOD CONTROL capacity of 381K acre feet, not to be confused with the water supply pool.)
January rainfall has been more than 300% of normal throughout much of the North Bay. (Image 2)
Here are the rainfall totals for the water year so far (Image 3), and the percent of normal for the water year so far. (Image 4)
Up in the Sierra, the snowpack is huge. Many places have reached their average snow water equivalent (SWE) for April 1st already, in mid-January. In fact, the Central Sierra Snow Lab near Donner Summit has set a new record for October to January snowfall.
Since December 26th, many parts of the high Sierra have seen 10-20 feet of snow. Since this graphic was created, 3-5 more feet have fallen near Tahoe. (Image 5)
Here is the percentage of normal snow water equivalent across the Sierra, where most sites are over 200% of normal. (Image 6)
Meanwhile, reservoirs across the state are rapidly filling, but years of punishing drought left them low before the onslaught of storms. The state’s biggest reservoir, Lake Shasta, is at 82% of average storage, a huge increase from a month ago, while Lake Oroville, the 2nd largest, is over 100% of normal storage for the date, as is Lake Sonoma, and many others across the state. Others, like Trinity, have a long way to go. (Image 7)
Don’t be confused by the numbers in blue. Those represent the total FLOOD CONTROL capacity of each reservoir, not the water supply pool.
After a small storm for Wednesday, high pressure finally builds back in. (Image 8) This should keep us mostly dry through the end of the month of January. (Image 9)
And, we should be on the cold side, as cold continental air seeps in from the north. (Image 10)
However, the models suggest that the high pressure center retrogrades to near the Aleutian Islands by the start of February. (Image 11)
This could allow storms from the north to dig south, reaching us. The long range models are suggesting this pattern may be likely, showing a return of above average rain in the first week of February. (Image 12)

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