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

Quincy Vagell
Published: January 2,2016
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 in the week ahead.
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: Sunday - Monday

An initial area of low pressure will swing a frontal boundary toward the California coast late in the day on Sunday, spreading showers and perhaps a clap of thunder down the coast through Sunday night, continuing into Monday morning.

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, New Mexico and southern Utah.
(FORECAST: L.A. | Las Vegas | Phoenix)

Round 2: Tuesday

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

Tuesday's Forecast

Rain reaches the California coast by morning and rapidly spreads rain inland. 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 perhaps parts of the San Gabriels with the potential for a foot or more of accumulation in some spots by Tuesday night. A bit of the rain and snow may make it as far east as northern Arizona, Nevada, Idaho and Utah.

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 locally heavy snow as far south as the Tehachapis, San Gabriels and Santa Ana Mountains of Southern California and some of the interior valleys of central to Northern 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 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, 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.
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