Heavy Rain, Feet of Snow Target California as ‘Miracle March’ Atmospheric River Weather Pattern Arrives

Weather

A “miracle March” parade of Pacific storms that may last well into the week ahead has begun soaking California and other parts of the West Coast.

This much wetter weather pattern will be accompanied by a so-called atmospheric river, or “Pineapple Express”, at times, unleashing bouts of heavy rain, feet of Sierra snow, and strong winds, high surf and coastal flooding at times through the new week ahead. Winds have gusted to as high as 88 mph as of Saturday evening at Mount Diablo, with reports of scattered wind damage across Northern California.  

Saturday night into early Sunday morning, roads were flooded around San Jose and Oakland. Mudslides also created traffic issues, including in Santa Cruz where a mudslide and basketball sized boulders blocked a south bound lane on highway 17.

Several locations in northern California picked up over an inch of rain from a weaker frontal system Friday into Saturday morning. By Saturday night, few higher elevations of Marin, Monterey, Santa Clara and Santa Cruz counties picked up over 4 inches of rain. As much as 5.47 inches was reported at Mount Umunhum. Lower elevations of the Bay Area picked up generally 1 to 2 inches of rain.

With the typical dry season quickly approaching as spring nears, this could be the last hurrah for the rainy season after a very dry February in the Golden State. However, this will also be too much of a good thing in some areas, resulting in flooding, mudslides and rockslides.

Below we look at what we can expect.

Forecast: Stormy Weather Continues This Weekend

The wettest, strongest Pacific front will slide down the coast through Sunday morning. A second storm system will then arrive Sunday afternoon in northern California, then linger into Monday in southern California.

As the graphic below shows, the ribbon of moisture, known as an atmospheric river, associated with this first storm will stretch from California to near and west of Hawaii. This will be ushered in by a strong jet stream with winds topping 200 mph in the high altitudes over the Pacific Ocean late this week.

Here’s what to expect through Monday:

• Most lower elevations will pick up an inch or more of rain in northern and central California. Foothill and coastal range locations will see several inches of rain.
• The heavy rain could result in some flooding, mudslides and rockslides even after seeing dry conditions the last month or so, particularly over areas burned by wildfires over the past year or two. Melting snowpack will also add to flooding of streams and rivers. Flood watches are in effect in parts of northern and central California.
• Up to 3 feet of total snowfall is expected in California’s Sierra Nevada above 7,000 feet. Snow levels may start at 7,500-8,000 feet before falling to valley floors Sunday morning, which would then affect travel through passes.
• A rather large area of strong winds is expected through Sunday morning from northeast Oregon into the Sacramento Valley, Sierra Nevada, and the adjacent foothills. Gusts may top out at 100+ mph over the Sierra ridgetops. The foothills could see gusts to 80 mph while valley wind gusts may hit 60 mph. Power outages and downed trees are possible.
• Rain and mountain snow will also impact Washington, Oregon, and much of the Intermountain West this weekend as the frontal system slides inland.
• Southern California will also see some rain in two rounds over the next several days. First from the storm into Sunday and then from a separate low-pressure system that is expected to impact the area Monday.
• Large, possibly damaging surf is expected this weekend into Tuesday. The National Weather Service in Oxnard, California, is mentioning the potential of moderate coastal flooding and damage to coastal structures. The threat of rip currents will be high, as well.

The National Weather Service is expecting significant impacts from this storm, which could be worsened by the fact that a drought is ongoing. “Considering the stress on trees due to the drought, we could see a fair number of trees downed with this storm,” the Sacramento, California office warned in a Friday evening forecast discussion.

Beyond Monday, various computer forecast models are depicting that several more storm systems will affect the West Coast through next week and beyond. However, it’s too early to provide specifics.

That said, we can provide a broad overview of the impacts we can expect in California during the extended forecast:

• It’s safe to say we’ll be measuring snowfall totals in feet in California’s Sierra Nevada from this weekend onward.
• Depending on how wet the storms are and how quickly they follow after each other, flooding could become widespread. Significant rises on rivers and streams are also likely.
• Mudslides and rockslides are probable, and may become numerous, particularly near burn areas.
• The lion’s share of the rain and mountain snow may impact the northern half of California rather than the south.

Our forecast rain and snow map through next Friday (March 11) illustrates the expectation of several inches of rain in the lower elevations and feet of snow in the mountains. The heaviest amounts are focused from northern and central California into the Northwest.

When looking at the Sierra Nevada in detail, there is the potential for 6 feet or more of snow at the highest elevations during the next 14 days. Keep in mind, however, that this is a very long range outlook so there is uncertainty, but it does provide an idea of the amount of snow we could see over the course of time.

https://weather.com/forecast/regional/news/california-atmospheric-river-snow-heavy-rain-flooding-march