Strong Storm Looms Late Week as California's Wet Season Begins to Come to a Close

Linda Lam
Published: April 4,2017
Big changes are ahead for California.
Much of the region will enjoy dry and warmer conditions until Thursday, but the next storm will then move in with heavy precipitation, gusty winds and mountain snow.
This next system comes toward the end of the state's wet season, which has delivered near-record precipitation.
(MORE: Where Winter 2016-17 Ranked)
An upper-level trough and a strong area of low pressure, especially for April, will approach the West Coast late week, spreading rain, higher-elevation snow and gusty winds across the region.

Current Satellite, Pressure and Moisture

This storm may be able to tap deeper sub-tropical moisture, resulting in moderate to heavy precipitation, especially in northern California, the Sierra and western Nevada on Friday. A few thunderstorms are possible.
(MAPS: Weekly Planner)
There is still some uncertainty regarding the exact track of this system and how much moisture will accompany it. Be sure to check back to weather.com for forecast updates as we get closer to this event.

Forecast Details

Showers will begin to spread into far northern California late Wednesday into Thursday, ahead of the potent low-pressure system that is expected to move onshore by Friday.
Thursday Night

• Rain will spread across northern and central California, and precipitation will become more widespread across the Pacific Northwest.
• Snow will fall in the higher elevations of the Sierra and Cascades.
• Winds will increase, with strong gusts likely in portions of northern California.
• FORECAST: San Francisco | Reno, Nevada | Medford, Oregon

Thursday Night's Forecast

Friday

• Moderate to heavy rain is expected for parts of central and northern California, as well as in the Pacific Northwest. A few thunderstorms may also develop.
• Snow will be heavy at times in the Sierra, including at pass level which will make travel difficult.
• Gusty winds are anticipated, especially in parts of Nevada, southern Oregon and western Utah.
• Showers may reach as far south as Southern California Friday night.
• FORECAST: Sacramento | South Lake Tahoe, California | Fresno, California

Friday's Forecast

Saturday

• Rain and snow may persist into Saturday for much of the West, before ending in most areas by Saturday night.
• Winds will decrease through the day, as well.
• FORECAST: Los Angeles | Redding, California | Seattle

Saturday's Forecast

Northern California will experience the chance for rain and snow showers into early next week, and another low-pressure system may bring another round of rain and snow to the region late Sunday into Monday.

How Much Rain and Snow Is Expected?

Snowfall will likely be measured in feet in the higher elevations of the Sierra, with some areas likely adding more than 2 feet of snow to the already hefty snowpack. Colder temperatures may allow snow to fall at elevations as low as 4,000 feet in parts of the Sierra by Saturday, although in the southern Sierra snow will generally fall above 7,500 feet.
This combination of heavy snow and gusty winds will make for hazardous travel, especially Friday into Saturday.

Rain and Snow Forecast

Much of northern California, as well as parts of central California, will receive 1 to 3 inches of rain through Saturday. Some areas along the coasts of northwestern California, Oregon and Washington, as well as the foothills of the Sierra, could see up to 8 inches of rainfall.
(MORE: Where March and April Are the Snowiest Months)
In some areas, precipitation from this system may exceed the average monthly precipitation for April. Sacramento usually receives about 1.15 inches of rain in April, and from Thursday through Saturday the current forecast is for around 1.25 inches.
According to the National Weather Service office in Reno, Nevada, the last time Tahoe City saw a two-day total of at least 2 inches of liquid precipitation in April was in 2003, and more than 2 inches in currently anticipated.

Flooding Concerns?

The ground in many areas is already saturated from the above-average precipitation that occurred this winter, and many rivers are already running high.
Oct. 1 to March 31 was the wettest on record in Sacramento, Reno and South Lake Tahoe, according to the Southeast Regional Climate Center. In the Pacific Northwest, this six-month period was also the wettest in Spokane, Washington; Pocatello, Idaho; Lewiston, Idaho; Kalispell, Montana; and Sheridan, Wyoming.
Typically, when April rolls around, the chance of big storms bringing heavy rain and snow decreases in California. Given the wet water year, it is no surprise that another strong storm system is poised to bring another round of precipitation through early April.
The water content in the snowpack throughout much of the West remains well-above average. As of April 4, areas of the Sierra and western Nevada are more than 200 percent of average for the date, according to the Natural Resources Conservation Service SNOTEL network.
When examining the snow-water content for the northern, central and southern Sierra, all areas are at least 145 percent to average for April 4, according to the California Cooperative Snow Surveys.
This year's snowpack is quite a change from the past few years, when drought prevailed across California.
When the upcoming heavy rainfall is combined with any snowmelt that takes place, courtesy of the recent warmer temperatures, and the saturated ground, this early April storm could result in flooding in some areas, especially for lower-elevation creeks and streams.
The saturated ground will add to the risk for landslides and rockslides in some spots, as well.
In addition, many reservoirs continue to run above average, including Lake Oroville, Lake Shasta, Sun Luis Reservoir and Pyramid Lake. Lake Tahoe continues to run above full pool, with a water level of 6,227.26 feet as of April 4.
(MORE: Spring Flood Outlook)
As the snow melts this spring, any heavy rain events could pose additional flood risks. Flooding concerns may also increase if the weather turns warm for an extended period of time this spring.

MORE: Southern California Wildflowers in Bloom, March 2017 (PHOTOS)

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