Unprecedented snowfall on US west coast is ‘once-in-a-generation’ event

The west coast of the US, from Oregon to the mountains of California and the golf courses of Phoenix, has received nearly unprecedented levels of snowfall this week in what officials are calling a "once-in-a-generation" event.

The mountainous regions of California have received so much snowfall - more than 40ft of snow since the start of the season - that entire towns have shut down as they are virtually cut off from the rest of the state. The governor has declared a state of emergency in 13 counties due to the unusual snowfall.

Portland, Oregon's largest city, saw its second snowiest day in history with almost a foot of snow, while further south in Arizona the suburbs of Phoenix received a dusting of snow.

"This rain and snow bucked the trend, and it's highly unexpected," said Ryan Maue, a meteorologist and former National Oceanic and Atmospheric Administration chief scientist. "It's like once in a generation."

The effects of the storms can be seen across the region. In California, the extreme weather has left thousands without power, closed Yosemite and Joshua Tree national parks, and caused avalanches. In Lake Tahoe, an avalanche hit an apartment building, forcing residents to evacuate. No one was injured in the 200-yard-wide snowslide, the local sheriff's office said, but it "engulfed the bottom two stories of the building".

Officials in tourist destinations in the Sierra Nevada have urged visitors to stay home rather than risk travel as roads remain dangerous.

Yosemite national park, which broke a 54-year-old daily snowfall record, has closed indefinitely.

Although the storms have overwhelmed the state, they have helped ease California's devastating drought. All of the state was experiencing a drought three months ago but now, according to the US Drought Monitor, more than half the state is out of drought.

Bianca Feldkircher, a meteorologist for the National Weather Service, said a persistent blocking pattern over the Pacific Ocean plus cold air migrating south from the Arctic have created the conditions for widespread snowfall along the west coast.

"Not only were you getting significant snowfall in areas that already see snow, you were also seeing snowfall on lower elevations in southern California, which is super rare," said Feldkircher.

For example, the forecast on 1 March warned of snowfall for parts of Phoenix, which Feldkircher said is "super unusual" for this time of year. And last week, Portland saw abnormally high snowfall rates and recorded nearly 11in (28cm) - the second snowiest day in the city's history.

With respect to human-induced climate change, meteorologists say it is challenging to nail down what part it is playing in the west coast's peculiar winter season.

But increasingly extreme weather is expected as global temperatures rise. "Heat produces moisture, moisture produces storms, and heat and moisture bind to produce even more severe storms," Feldkircher said.

Forecasting technology keeps getting better. So much better, it may even soon be able to forecast extreme events with higher accuracy. "In the near future, I do not think climate will cause issues with our weather forecasting capabilities," said Maue.

Although many regions struggled with the challenging winter conditions, some are welcoming the much-needed moisture.

The recent precipitation is a blessing for ameliorating the drought that has persisted in the south-west.

California tends to go from rags to riches, bounty to poverty when it comes to rain, Maue said. "That's why from a policy point of view, you need to be able to have water regulations, reservoirs and water supplies that can last during multi-year droughts."