Get ready for a wild weather ride across the American West! The extreme warmth and dry conditions that have dominated the region are about to take a backseat as a cooler and wetter pattern moves in. But here's the catch: it's a partial relief at best, with record-low mountain snowpack still a major concern.
The winter so far has been nothing short of extraordinary. Record-breaking warmth has engulfed most of the Western U.S., with the exception of a few areas like California's Central Valley, which experienced unique tule fog episodes. Precipitation has been a mixed bag, with some parts of central and southern California experiencing record-breaking wetness, while other areas in the interior West and Rocky Mountains have been exceptionally dry.
As a result, western U.S. snowpack has reached unprecedented low levels for February. Every single western watershed is currently below average in snow water equivalent. There are a few high mountain regions, like the southern Sierra Nevada and northern Rockies, that have managed to hold on to near or even above-average snow water storage, thanks to heavy precipitation earlier in the season. But overall, snowpack conditions are as bad as they've ever been in recorded history across the entire Western U.S.
The unusual warmth has led to spring-like, and even summer-like, conditions from southern California all the way to the Front Range of the Rocky Mountains. Plants, animals, and skiers have all been behaving strangely, and tourism in mountain towns has taken a hit. Concerns about wildfire risks and water supply for the upcoming months and seasons are growing, especially in the interior West and Pacific Northwest.
Meanwhile, the eastern U.S. has been dealing with one of the coldest two-week periods in decades, with disruptive and deadly ice and snow storms. All of this can be attributed to the persistent "Warm West/Cool East" pattern, characterized by a strong ridge in the Western U.S. and a trough in the Eastern U.S., coupled with a "Warm Arctic/Cold Continents" pattern where the polar vortex has been weak, allowing bitter Arctic air to escape and move towards continental regions.
But here's the good news: a major pattern change is on the horizon, and it's bringing cooler temperatures and much-needed rain and mountain snow to most of the U.S. West. The question is, will it be enough to alleviate the severe snow drought that the region is facing?
The first Pacific weather system is expected to arrive in central California on Tuesday, packing a decent punch. A slowly-deepening surface low will make landfall near San Francisco, bringing widespread rain and gusty winds. While the greatest impacts will be felt near and south of the low's landfall, including the SF Bay Area and the I-80 corridor, the entire state can expect some precipitation. This system, though initially warmer than average, will have enough cold air behind the cold front to bring Sierra snow levels down to more reasonable and seasonal levels.
This initial system will weaken after passing over California, missing the Pacific Northwest entirely. The interior West will have to wait a bit longer for more substantial precipitation and cooler temperatures, but they are expected to arrive in the near term.
There is uncertainty about the details, but there is a high likelihood of additional and possibly larger/stronger storms along the West Coast and across the interior West in the upcoming cycle. The persistent ridge will be replaced by a quasi-stationary trough along the West Coast or just offshore, creating a favorable setup for recurring precipitation events. This high-energy pattern is expected to bring one or two strong low-pressure systems with associated cold frontal passages, potentially resulting in widespread moderate to heavy rain, strong/gusty winds, and heavy mountain snowfall.
While this pattern may not bring Arctic-like cold, it will still be much cooler than the near-record warmth experienced recently. It should be cold enough to allow for respectable snow accumulations across most major mountain ranges in the West over the next 10-14 days, keeping pace with usual February snow accumulation and making up for a portion of the season's snow deficit, especially in places like the central and southern Sierra. However, it's unlikely that this pattern will completely erase the huge and often record-breaking snow deficits that currently exist in many areas.
The ongoing marine heatwave off the coast of California, which has intensified during January's calm weather, will likely influence the incoming storms. The warm ocean waters can add moisture to the lowest levels of the atmosphere and provide additional potential energy to storms, potentially intensifying localized downpours and thunderstorm activity. This could result in higher precipitation rates and slightly elevated snow levels.
Beyond this 1-2 week storm cycle, there is high uncertainty about the rest of February. There are indications of another major polar vortex disruption, which could lead to a wavy/amplified jet pattern over the Northern Hemisphere. If a strong and persistent blocking ridge develops over the North-Central Pacific, a large cold air mass could once again form over western Canada. The subsequent movement of this cold air mass will depend on the broader hemispheric pattern, which could either bring a re-emergence of the warm West/cool East pattern or allow late-season Arctic air to move southward into the U.S. West.
Stay tuned for more updates and join the discussion on YouTube as we delve deeper into the upcoming pattern change, the mountain snowpack situation, and the potential impacts on the Western U.S.!
And this is the part most people miss: the extreme weather events we're witnessing are a stark reminder of the impacts of a warming planet. As we navigate these weather whiplashes, it's crucial to stay informed and engaged in the conversation about our changing climate.
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