CALIFORNIA - A shift in the Pacific pattern is underway this week, with warm atmospheric rivers beginning to edge farther south and bring a return to rainfall across northern parts of the state. The change will also help break up the persistent fog layer that has kept many low-lying areas locked in a prolonged inversion and unusually chilly daytime temperatures.
According to analysis from Weather West and Meteorologist Daniel Swain, the incoming moisture is tied to a subtropical airmass capable of finally lifting the trapped cold air near the surface. As the inversion erodes, temperatures at lower elevations may rise by 10–20°F, even as cloud cover and intermittent rain develop. Precipitation is expected to spread gradually inland through the week, with light to moderate warm rainfall marking the first notable pattern shift in several weeks.
Swain notes, however, that this warmth has consequences for higher terrain. Snow levels remain extremely elevated, often between 7,000 and 9,000 feet or more, meaning most mountain locations will see rain rather than snow. With existing snowpack already at historically low levels for December in several regions, warm rain may diminish what little accumulation remains.
Farther north along the Pacific Coast, a series of strong atmospheric rivers continues to impact Washington and British Columbia, producing renewed flooding and landslide concerns as saturated slopes absorb additional moisture. Meanwhile, southern parts of the state will stay dry and warm for now, though longer-range ensemble guidance suggests the potential for broader storm activity later in the month as the ridge slowly shifts east.
While the transition is gradual, the overall trend points toward a wetter pattern returning to the state, with the possibility of more expansive storm systems developing closer to the end of December.
Keep checking ANUK for continued weather developments and regional insights.
