Summary:
- October was warmer than average[1] across the vast majority of the western US, especially in California and the Great Basin but closer to average in the PNW and across the northern Rockies.
- October was also dry for the bulk of the western US, except in portions of eastern Washington and northern Idaho and Montana.
- With a slow start to the fall rainy season, on top of a weak monsoon season and record high temperatures for many, the western US drought footprint is now above 90%, with nearly 60% in severe to exceptional drought. The forecast through the first half of winter is for much of the west to remain dry, with the exception of the PNW which is forecast to see a reasonable start to early winter rains.
- The ridge of high pressure that has brought a warm and dry end to October and start to November is expected to give way to a few weak cold fronts out of the North Pacific, but also the chance for a couple of Arctic air mass incursions during early November. The result will likely be a relatively cold second week to mid-month period. Precipitation amounts will be light for most, but relatively heavy for the PNW and into British Columbia.
- The forecast for November through January is largely based on the La Niña conditions in the Tropical Pacific and a relatively warm North Pacific. As such, the PNW is anticipated to see near average to slightly cooler and wetter first half of winter, while California is expected to be warmer than average and near average to drier than average through December.
