A snowy, rainy storm is hitting California. Will it curb the coming fire risk?

A powerful late-season storm system is hitting California and the intermountain west, and over the next several days will dump several feet of high-elevation snow in the Sierra Nevada and deliver multiple inches of rain up and down the coast.

The storm arrived into a very warm air mass, with temperatures running 5 to 15 degrees above normal on Thursday and Friday before the system’s arrival. The earliest fragments of the system delivered heavy showers and thunderstorms to Northern California and southwest Oregon.

While the back half of the storm will feature plenty of cold air and mountain snow, it ran into a warmth emblematic of the recent season. Persistent and record warmth has fueled a rare snow drought in California and the Western United States more broadly – conditions that are setting up the region for a problematic summer of wildfire risk.

Storm may be biggest in months

Including some heavier rain that fell from the Bay Area northward through Friday, coastal regions in Northern California could end up with 2 to 4 inches of rain. About a half-inch to an inch is expected into Southern California. A soaking is also anticipated in the Central Valley, where a weak tornado threat was present with thunderstorms Friday.

The heaviest precipitation is expected to fall in higher elevations, with total liquid equivalent (melted snow plus rain) as high as 6 inches or more in the mountain peaks west of Lake Tahoe.

As much as 2 to 3 feet of snow will be common at elevations above 7,000 feet, where winter storm warnings are in place. Snow levels that were as high as 10,000 feet to start the storm are expected to drop to about 4,000 to 5,000 feet by the colder part Saturday night through Monday.

Travel in the mountains will become treacherous, with wind gusts as high as 60 to 80 mph causing whiteout conditions.

This follows a March that had basically no snow for most of the region. While there was a minor storm to open April, any snow has mostly melted. The last significant snow fell in mid-February, and it followed a dry spell lasting several weeks.

Will the storm help the snowpack?

Early April is when western mountains tend to reach peak snowpack for the winter. This year, fire weather is already a concern.

“Current Sierra snowpack is the lowest on record,” said Daniel Swain, a climate scientist with the California Institute for Water Resources. “The mountains have lost whatever accumulated in early April.”

According to April 10 data from the California Department of Water Resources, the whole Sierra chain was running 15 % normal of snow water equivalent, with the northern Sierra only at 5 % normal. Many typically snow-filled spots are bare or close, something that doesn’t usually happen until June or July.

Persistent warmth, including the record-breaking heat of March, led to a historically early melt.

“What should be gradual snowmelt happened suddenly weeks ago,” said Karla Nemeth, director of the California Department of Water Resources.

Swain pointed out that unlike some other poor snowfall years, it wasn’t a very dry winter in California. In fact, the cool season through December was running at record-wet levels across the southern half of the state in particular.

“It was so astonishingly warm, much of the precipitation fell as rain, even in places where it also eventually fell as snow,” Swain said. “Then the snowpack just melted away. It has been more like in the East Coast, where snow lasts just a few days. This winter was like that at 7,000 feet in the Sierra.”

California has been dry, but drought is not the main concern

After becoming fully drought free – the first time in 25 years – around the start of the year, California has seen abnormal dryness spread anew, with some low-level drought creeping into the northern Sierra, according to the U.S. Drought Monitor. The historically strong March high pressure, which blocked moisture and delivered widespread record-high temperatures, is largely to blame.

But despite the recent dry spell, reservoirs are at or above average across California.

“By some definitions, California is not really in a drought,” Swain said.

He pointed out that the real drought problems in the West are across the Great Basin and particularly the Rockies.

In the Colorado River Basin, he noted that it’s not just record dry, but current snow water equivalent is less than half the previous low point at this time of year.

Even with somewhat better conditions in California, there are growing concerns, ranging from fire potential to confused plant and animal life.

“Phenology is messed up. Animals are wondering what is going on. And it does not take a severe drought to create severe wildfire issues,” Swain said.

Is a bad fire season baked in?

This storm is the main precipitation expected in the foreseeable future. There is a chance the weather pattern will remain somewhat conducive for at least some occasional rain and very high elevation snow through the rest of the month, but that is uncertain. And any additional storms are unlikely to change the trajectory.

The current forecast from the National Oceanic and Atmospheric Administration calls for a warmer-than-normal summer in the Western U.S. With that, there is the likelihood of little precipitation – a recipe for trouble.

“Much of the West could have a very long peak fire season this summer,” noted the National Interagency Fire Center forecaster for the April podcast of Predictive Services.

Its outlook indicates there will be above-normal fire potential in the Sacramento Valley and Bay Area mountains starting in May. Above-normal fire risk is then expected to expand in June and July to cover most of Northern California. Wildfire forecasts beyond July are not yet available, but hot and dry conditions mean the threat is likely to persist.

A zone of atypically warm water to the west and southwest of California may be a wild card into the summer, noted Swain. Even before what could be a major El Niño event gets cranking, waters are running as much as 5-plus degrees warmer than typical.

Whether that means injections of needed moisture deliver rainfall that stymies peak summer fire season or it just sparks lightning storms in crispy forests is yet to be determined.

“It does raise the odds of unusual summer weather in the Southwest,” Swain said. “It may also lead to potential for an anomalous summer or autumn rain event from remnants of tropical storm, not unlike Hilary.”