Winter Storm Kori to Produce Feet of Sierra Snow and Flooding Rain in California

Linda Lam
Published: January 20,2017
Winter Storm Kori began its pounding of the West Tuesday with an ice storm and will spread heavy mountain snow and rain into storm-weary California into Saturday, thanks to another atmospheric river that has set up over the region.
(MORE: Winter Storm Central | How Winter Storms Are Named)
Winter storm warnings have been posted for snow in the Sierra and in parts of the inter-mountain West, including Arizona's Mogollon Rim.

Winter Alerts: West

More than 3 inches of rain in the Sherpa Fire burn area west of Santa Barbara, California led to mudslides. Cabins and cars were washed away after heavy rainfall there on Friday.

Current Radar, Temperatures, Conditions

The Setup

On the heels of a period of flooding and prolific snow last week, another deep plume of moisture known as an atmospheric river has pushed ashore along the West Coast.

Pacific Atmospheric River Watcher

Kori will then push into the Rockies, raising the threat of flooding rain, more heavy mountain snow and, in some areas, more freezing rain and sleet.
Let's get into the particulars of this forecast, starting with timing, then with potential flooding, snow and ice impacts.

Saturday

• Pockets of snow will persist in the Four Corners, Central Rockies, mountains of southern California, Sierra, Siskiyous and Cascades.
• Some light snow, associated with Kori's first phase, may blanket parts of the northern Plains.

(FORECAST: Flagstaff, Arizona | Salt Lake City | Albuquerque)

Saturday's Forecast

If that wasn't enough, yet another powerful Pacific storm lurks behind Kori for Sunday with more rain and mountain snow, including in southern California. For more on that story, click the link below.
(MORE: New Storm to Close the Weekend)
Kori will also bring mainly rain to the Northeast early next week, but interior parts of the region could see snow, sleet and freezing rain. For more on the impacts Kori may have in the Northeast, click the link below.
(MORE: Winter Storm Kori Will Bring Mostly Rain, Wind to the Northeast)

How Much More Snow and Rain?

Fortunately, snow levels in the Sierra won't nearly be as high with Winter Storm Kori, and the atmospheric river won't nearly be as potent to trigger the kind of flooding we saw last week.
Despite that, a swath from western Oregon to California, including the Sierra foothills below snow level, will likely see at least an inch of rain through Saturday. Much higher amounts are likely in the coastal ranges. Additional flooding is possible, especially in burn areas.

Rain and Snow Forecast

Water levels in most of northern California have dropped, and given the recent storm track and cold weather, water levels in rivers and streams in western Washington and northwest Oregon are below normal for mid-January.
However, that steady, at times heavy, rain is likely to trigger at least some river flooding the next several days on the most flood-prone rivers.
Fortunately, Kori won't dump another 10-plus feet of snow in the Sierra, but another 1 to 3 feet are likely through Saturday.
Other parts of the West, including the Cascades, mountains of Idaho and northeast Oregon, southern California mountains and the high country of the Four Corners may pick up a foot of snow through Saturday. This includes parts of Arizona's Mogollon Rim and the Grand Canyon.
If all that wasn't enough, high, possibly locally damaging, surf is expected along parts of the California coast into early next week.

Ice, Sleet and Snow Reports

Mammoth Mountain in California's southern Sierra Nevada had picked up 20 to 30 inches of snow from Kori, as of early Thursday. The ski resort said this winter storm has vaulted them to their snowiest January on record.
As expected, the heaviest ice accumulation has been in the Columbia River Gorge and upper Hood River Valley.
A report of 2 inches of ice accumulation came in Wednesday morning from North Bonneville, Washington, between Hood River and Portland, Oregon. The ice has reportedly broken lots of tree limbs in the area. A 2-inch ice measurement has also been reported near Snowden, Washington.
(NEWS: Winter Storm Kori Becomes Icy Mess for Northwest Travel)
Hood River, Oregon, measured 1.5 inches of ice accretion, while Stevenson and Underwood, Washington, both reported 1 inch of ice accumulation.
Precipitation changed over to rain in the Portland, Oregon, metro area by late Tuesday evening, but not before 0.64 inches of ice accumulated at the airport.
(MORE: America's Most Winter-Weary City)
Elsewhere, one-quarter of an inch of ice accumulation was observed near Wenatchee, Washington, followed by 3 inches of a snow/sleet mix.
Up to one-quarter of an inch of ice was also measured near Spokane, Washington, with up to 3 inches of snow/sleet on top of it. Precipitation changed to rain early Wednesday morning in Spokane.
Ahead of the first Pacific front of Winter Storm Kori, winds have gusted as high as 87 mph on the Yaquina Bay Bridge in Newport, Oregon.

A "Mixed Blessing" of Drought Relief

Last week's heavy rain and feet of Sierra snow effectively wiped out the California drought north of Interstate 80, which had been in place, there, since Dec. 20, 2011.
A big player in California's water supply is spring snowmelt of the Sierra's snowpack. Fortunately, thanks to the recent barrage of storms, the water content of the Sierra snowpack is now almost double the average for mid-January.
Furthermore, reservoir levels in most of the state's major reservoirs are near or above average for this time of year.
However, parts of southern California remain in an extreme to exceptional multi-year drought.

Current Drought Status

Drought relief in southern California is more tricky, often posing a Catch 22.
While some rain is good to moisten soil and vegetation to reduce any fire risk, a wet winter season can fuel the growth of brush that can serve as fuel for wildfires during the summer/early fall dry season.
Furthermore, heavy rain in southern California has two additional impacts:

• Flash flooding triggered from rapid runoff over impervious surfaces in the L.A. Basin's "concrete jungle."
• Debris flows over recently-burned wildfire scars. 

The rain rates needed to trigger debris flows in southern California, according to the U.S. Geological Survey, are as low as 0.2 inches per hour.
So, the reality of the situation is, unless the storm's water ends up in a reservoir, one could argue that despite the drought this upcoming barrage of storms may be more headache than helpful for southern California.
Parts of southern California including San Diego, Santa Barbara, and the valleys surrounding Los Angeles had flooding on Friday, Jan. 20. Widespread totals of 2-5 inch