- A persistent ridge of high pressure over the west in December produced strong inversions and stagnant air resulting in cooler conditions in the valleys and warmer conditions in the mountains. Another result of the ridge is that the month will go down as one of the driest Decembers on record in many locations in the west.
- The persistent ridge appears to be close to breaking down as of this report and will likely usher in more seasonally normal precipitation patterns in the west and bring a much needed warm up to the east.
- The seasonal forecast from January through March continues to tilt the odds to winter being cool/wet in the PNW and cool to average and dry in California. However, it takes a lot to make up for a dry December and while a near normal snowpack could still arrive for many areas, the odds of a normal winter for precipitation decreases daily and is currently running around 20% for central to southern California, increasing to 50-70% in northern California and Oregon, and to 70-100% in Washington.