Series of Storms to Bring Plenty of Rain, Snow to California

Quincy Vagell
Published: January 3,2016
The next series of storms to impact the West Coast will be a bit different than what the region has experienced in recent months. This go around, even Southern California can expect a decent helping of much-needed rain.
For parts of the Cascades, Siskiyous and Sierra, as well as parts of the Four Corners and Desert Southwest, expect hefty amounts of snow to pile up into the coming week.
This will add to a Sierra snowpack that is much more substantial than at the same point last year.
According to winter weather expert Tom Niziol, through Dec. 30, 2015, the Sierra snowpack was at 105 percent of normal for the season, compared to just 50 percent through the same date in 2014.

Stormy Pattern Ahead

A powerful Pacific jet stream will direct a series of Pacific frontal systems into the West Coast through this week.
While none of them appear to be particularly strong or wet, the aggregate sum of rain and snow from all these systems may become impressive by next weekend.
Here's a look at what you can expect.

Round 1: Through Monday

An initial area of low pressure will swing a frontal boundary toward the California coast late Sunday, spreading showers and perhaps a clap of thunder down the coast through Sunday night, continuing into Monday morning.
Moisture from this system will also continue to impact parts of western Oregon and southwest Washington into Sunday night, where a mixture of snow, sleet and freezing rain is affecting parts of the I-5 corridor. The Portland, Oregon area experienced snow and freezing rain through much of Sunday. Light snow fell in Seattle as well, beginning around midday Sunday.
A winter weather advisory has been issued by the National Weather Service into Monday morning for parts of northwest Oregon and southwest Washington. Although accumulations should be light, the snow and/or ice could contribute to slick travel conditions.

Monday's Forecast

Through the day on Monday, as the weak front and upper-level disturbance push inland, areas of valley rain and mountain snow will spread into parts of Arizona, southern Nevada, western New Mexico and southern Utah.
(FORECAST: L.A. | Las Vegas | Phoenix)

Round 2: Late Monday - Tuesday

As quickly as the first system fades away, a wetter system will sweep into California late Monday through Tuesday.

Tuesday's Forecast

Rain reaches the northern California coast by late Monday and rapidly spreads southward into Tuesday. Some of the rain may be locally heavy, particularly in locations that need it the most, across central California. Here, exceptional drought conditions continue, but modest dents in the long-term rainfall deficits are likely.
Unfortunately, the rain could become excessive in Southern California, leading to flooding of urban/poor drainage areas as well as potential debris flows of burn scars left by recent wildfires.
(Forecast: San Diego | San Francisco)
A period of heavy snow appears likely over parts of the Sierra, Siskiyous and the Southern California mountains with the potential for a foot or more of accumulation in some spots by Tuesday night. Snow levels in Southern California will be roughly 5,500 to 6,000 feet. In the Sierra, snow levels will be lower, ranging from 4,000 to 6,000 feet. Gusty winds are also possible, especially on exposed ridgetops and near the crest.
Winter storm watches have been issued for the Sierra Nevada, portions of central and southern Nevada, as well as the Southern California mountains.
The rain and snow will push east into Arizona, Nevada, Idaho, Utah, southwestern Colorado and western New Mexico by later Tuesday and Tuesday night.

Wednesday - Friday

Computer model forecasts differ in the details into the middle of the week, as can be expected, but another round of rain and mountain snow should impact the West in the Wednesday through Friday timeframe.

Wednesday's Forecast

As colder air is projected this system, snow levels are expected to lower. This could result in snow at elevations as low as 4,000 feet in the Tehachapis, San Gabriels and Santa Ana Mountains of Southern California.
Additional snowfall is also likely across much of the Intermountain West through Thursday or Friday with some of that moisture likely reaching the Rockies as well.
Behind this system, another rather quick-moving frontal system may target mainly northern California and the Pacific Northwest next weekend.
Through Friday, 1 to 2 feet of snow seems a good bet in much of the Sierra. Heavy snow in excess of 6 inches is possible across some of the higher elevations of northern Arizona Mogollon Rim, the canyonlands of southern Utah, higher elevations of southern Nevada, southwest Colorado and western New Mexico.
(Forecast: Lake Tahoe | Flagstaff)

Forecast Rain and Snow Through Thursday

For rainfall, widespread 1- to 2- inch amounts should be common across much of the California coast (higher totals in the foothills), from north of the Bay Area to Southern California, including L.A. and San Diego. Some one-inch-plus amounts should also spill over into the parts of California's central valley, as well as the low deserts of southern Arizona, including the Phoenix metro.
One fact mitigating the flood threat is that rain will be spread out over the course of the week from multiple modest systems, rather than one deep, slow-moving system with a tropical tap of moisture.
However, it seems likely that at least some local flash flooding will occur in urban/poor-drainage areas. Debris flows on burn-scarred hillsides from recent wildfires are also possible. Keep in mind it does not take heavy rainfall to trigger these mud and debris flows.
Since this is a complex setup with multiple storm systems expected to impact the region, continue to check back with weather.com for the latest information.
MORE: Seven Wonders of California