As snow fell Thursday in parts of LA where it hadn’t snowed for decades, Angelenos tried to make sense of the rare event. If the city is getting hotter due to climate change, how could it still get cold enough to snow? Or was this the type of extreme weather that LA should start to expect from a changing climate?
Rising average temperatures are absolutely to blame for the fact that the LA region sees less annual snowfall than it used to, but climate change is not responsible for Thursday’s snow event, climate scientist Daniel Swain tells Curbed.
Think of it this way instead, he says: Climate change is the reason LA got a dusting instead of inches.
“Up until 20 years ago, this would have happened every five or 10 years,” says Swain. “If it had been 50 years ago, more of the city might actually have seen more accumulated snowfall because it would have been a degree or two colder.”
In recent years, scientists who study climate change’s influence on extreme weather (a field known as “attribution”) have been able to directly tie warming temperatures to more powerful hurricanes and heavier rainfall events. For California’s climate, one phenomenon that scientists say warming temperatures have exacerbated is “precipitation whiplash”—very dry periods followed by very wet periods, with rapid transitions between them.
Although a warming climate does result in more snow in some places, LA is not one of those places, says Swain.
This week’s storm was also not one of the Pacific-based, moisture-charged winter storms fueled by higher ocean temperatures—those atmospheric river events which have a new scale to categorize their strength. Instead, it was a frigid, dry airmass with very little moisture that came from the north. The snow—or hail, or graupel—was created by the presence of very cold water very high in the atmosphere.
That’s not unheard of in LA, Swain noted. Widespread reports that LA had not seen snow for 70 years were not quite correct. In 1989, much of the western San Fernando Valley was blanketed in up to five inches of snow, and the mountains above Malibu saw snow just over a decade ago.
While outlying areas may continue to see flurries, true snow days are numbered in the LA Basin, says Swain. Downtown LA received a dusting for two days in 1962, and some measurable snowfall in 1949, but the last time the LA Basin saw actual accumulation—about two inches, what Swain considers “plowable snow”—happened all the way back in 1932.
“It’s vanishingly unlikely that we’ll ever see that situation again in LA,” says Swain.
Brian Kahn, a meteorologist at NASA’s Jet Propulsion Laboratory, agrees that Angelenos should not expect to see snow fall on City Hall again.
“I’d say the probabilities are going way down with climate change,” he tells Curbed.
Not only are snowfall events in the LA area becoming less common due to warming temperatures, the average snow line for the region is retreating to higher elevations, says Kahn. “Even at 2,000 to 4,000 feet, these events are also becoming less frequent.”
But something meteorologically interesting did happen during this storm, which Kahn thinks resulted in snow falling at elevations as low as 700 feet—and even at sea level at some Malibu beaches.
“Little thunderstorms in the cold air can bring down the snow level a little more,” he says.
This week’s temperatures, while chilly, used to be more frequent, says Swain. He thinks the reason the cold snap felt so jarring is because Angelenos have become accustomed to living in a place where temperatures have been significantly above average.
For the LA region, the last five years have been the five warmest on record. Swain says that changes our baseline for what feels normal.
“It’s starting to feel like the cold temperatures are weirder and more unusual,” he says. “And it’s feeling like the warm temperatures are not that rare at all.”