A significant weather pattern is emerging over North America, with a 'Warm West/Cool East' dipole developing in late January. This phenomenon is causing record-low snowpack in the Western U.S., particularly in California, where temperatures have been unusually warm. The Central Valley, an exception to this warmth, has experienced tule fog, keeping conditions colder and damper. Despite a wet start to the season in the Pacific Northwest and Southern California, the overall trend remains warm and dry, with no significant cold outbreaks expected in the near future.
The snowpack situation is dire across most of the West, with every Western state reporting record-low values for mid-January. The Northern Rockies and Southern Sierra are the only regions where heavy precipitation has somewhat mitigated the effects of record warmth. However, snowpack levels are far below average, with record lows in numerous locations, especially in Utah and Colorado, but also widespread elsewhere, particularly at lower elevations.
In California, high-elevation sites have above-average snow water equivalent due to near-record precipitation, while lower-elevation sites are nearing record lows. The Tahoe Basin's higher elevations are currently stable, but lower elevations are suffering. The northern Sierra/southern Cascades and Shasta region also have near-record low snowpack levels.
The upcoming 10 days will likely see further deterioration of Western snowpack, with conditions expected to remain warm and dry, followed by wetter but still warm conditions. By February 1, a majority of observing sites may reach record-low values. This 'Warm West/Cool East' pattern is a result of a highly amplified North American weather setup, with a strong ridge over the West Coast and a deep trough over eastern North America, creating extreme thermal contrasts.
California can expect mostly warm and dry conditions over the next 10 days, with scattered showers possible in Southern California later this week. However, there's high uncertainty regarding a potential pattern change in late January, which could bring warm subtropical rains, but may not significantly improve mountain snowpack. The weather pattern is influenced by a combined positive Tropical/Northern and negative Arctic Oscillation, leading to locally extreme cold air outbreaks in the East and persistently warm conditions in the West.
There are growing indications of a rapid transition towards El Niño conditions in the tropical Pacific by spring or early summer. The latest 'superensemble' blend update suggests a high confidence level in this outcome, with a slight chance of strong El Niño conditions by June. This aggressive forecast is supported by observational trends, including persistent westerly wind bursts in the tropical western Pacific and a substantial oceanic subsurface warm water mass moving eastward. This transition could impact California and western weather as soon as April or May.
Join the Weather West YouTube channel for a live discussion on Wednesday, January 21, at 12 noon Pacific Time, where we'll delve into the causes and implications of the record-low Western U.S. snowpack and the developing El Niño conditions.
