Summary:
- Near average* to colder than average December for much of the western US.
- A favorable shift in the jet stream in December brought considerable precipitation to portions of California while the PNW saw near-average to slightly above-average precipitation for the month.
- The forecast for January calls for a wet first half of the month for most everyone, especially California where a whiplash from dry to extremely wet conditions is hammering the state. Flooding will likely be in play as the atmospheric train continues its path into California. Right now, the second half of the month appears more likely to be average to drier than average but forecast models do not have a consistent signal yet for the second half of the month. However, models agree that temperatures for January will most likely be seasonal to below average.
- Even with some promising winter precipitation, drought conditions continue for over 90% of the western US currently. The winter forecast continues to show some improvement in the PNW and northern Rockies, however, even with the major inputs from the current circulation, California, the Great Basin, and the southwest are likely to remain in some level of drought through the winter and into spring.
- Current conditions show how a La Niña weather forecast can go bust when Artic blasts bitter cold air southward. However, forecasters expect conditions to flip back to cool and wet in the PNW and average to cool and dry south into California and the southwest for the rest of the winter. Forecasters are also expecting La Niña conditions in the Tropical Pacific to give way to neutral conditions in spring with some hints at El Niño in late summer or fall. The PDO remains in a strong negative phase with cold near-shore SSTs along the western coast of North America.
