Summary:
- Warmer than average to average for the month of December over California, Oregon, Washington, and Idaho with the Four Corners region cooler than average.
- The bulk of the western US was drier than average for the month of December. Late month storms brought near average to slightly above average precipitation to the PNW.
- Drought concerns continue over much of the west with over 65% of the area in severe to exceptional drought. Some improvement in drought conditions in the PNW, but longer-term concerns continue for California and the desert southwest.
- Active jet stream bringing storms into the western US over the next 10-15 days of the month. Precipitation amounts will be greatest from northern California into the PNW, while temperatures should remain average to slightly warmer than average. Models are hinting at a late month ridging event over the west, which would block storms moving southward and add to an already dry winter for California and the desert southwest.
- The forecast for the second half of winter continues to be strongly influenced by La Niña conditions in the Tropical Pacific. As such, the PNW across the northern states are forecast to be near average to slightly cool and wet, and California and the central to southern states are forecast to be warm and dry
