Another atmospheric river set to move across California, bringing heavy rain and snow

Just three days after a powerful atmospheric river (AR) event brought heavy rain to parts of California, leaving at least 2 people dead and nearly 10 000 under evacuation orders, another AR will reach the region late Monday, March 13, 2023, bringing more risk of flash flooding and heavy mountain snow through Wednesday.

• Rain in low elevations and foothills, and snow at high elevations, from northern to central California, as well as northwest Nevada, and Oregon is expected into Monday at a slightly lower intensity.
• Rain and snow will intensify late Monday into Wednesday, with considerable flooding impacts below 1.5 km (5 000 feet) elevation across much of the California coast and Central Valley, and over the southern Sierra Nevada foothills into midweek.
• Heavier rain, snow, and snowmelt are likely midweek, resulting in more widespread flooding from Tuesday into Wednesday, particularly in low elevations and areas with shallow and warming snowpack. Creeks and streams will continue to be vulnerable to flooding from additional rain and snowmelt.
• Heavy and wet snow is expected mid-week at higher elevations in California, particularly the Sierra Nevada, which will further compound snow load impacts and issues.

Onshore flow will produce coastal rain and highest-elevation snow over parts of California and the Pacific Northwest through Wednesday, NWS forecaster Ziegenfelder noted.¹

The storm will produce rain in low elevations and foothills and snow at high elevations from Northern to Central California and northwest Nevada and Oregon.

The rain and snow will intensify late Monday into Wednesday, creating considerable flooding impacts below 1.5 km (5 000 feet) elevation across much of the California Coast and Central Valley and over the southern Sierra Nevada foothills into Wednesday.

The additional heavy rain and snowmelt will result in more widespread flooding from Tuesday into Wednesday, particularly in low elevations and areas with increasing temperatures impacting snowpack.

Creeks and streams will continue to be vulnerable to flooding from additional rain and snowmelt.

Another round of heavy snow, measuring in feet in the higher elevations in California, particularly the Sierra Nevada, will further compound snow load impacts and issues.

As a result of the heavy rain, the WPC has issued a Moderate Risk of excessive rainfall over portions of Northern California and southwestern Oregon through Tuesday morning. The associated heavy rain will create numerous areas of flash flooding. Furthermore, many streams may flood, potentially affecting larger rivers.

The heavy rain will continue on Tuesday, therefore, the WPC has issued a Moderate Risk of excessive rainfall over parts of Central/Southern California through Wednesday morning. The associated heavy rain will create numerous areas of flash flooding. Many streams may flood, potentially affecting larger rivers, NWS warns.

This is the second atmospheric river to impact California within just 4 days. The first impacted the state on Thursday, March 9, delivering heavy rainfall across the central and northern parts of the state, and prompting the Weather Prediction Center to issue a Level 4 of 4 warning of excessive rainfall in the area. The storm left at least 2 people dead and nearly 10 000 under evacuation orders.

Dangerous excessive rainfall event underway across much of Central California, widespread severe flooding expected

Meanwhile, residents in many of California’s mountain communities remain trapped by snow from back-to-back winter storms that affected California in February. As of March 13, the number of fatalities stands at 11 but it’s unclear at the moment how many of those were directly related to snowstorms.

At least 4 people were found dead in their homes in the Big Bear area of San Bernardino County.²

Residents and local leaders have said that they were unprepared for the powerful storms that first arrived on February 21 and ultimately surrounded homes in snow drifts as tall as 3 m (10 feet).³

Many began running low on food, fuel and medications. Some endured power outages, while a handful of fires are believed to have been sparked by broken gas lines.

‘HELP US!!’ message written in snow spotted in Crestline after winter storm strands thousands of people, California

References:

¹ Short Range Forecast Discussion – NWS Weather Prediction Center College Park MD – 342 AM EDT Mon March 13, 2023

² 2 dead, nearly 10,000 under evacuation orders as California floods intensify – CNN – March 10, 2023

³ Death Toll Rises in Southern California Mountains After Blizzards – The New York Times – March 8, 2023

Featured image credit: NOAA/GOES-West, RAMMB/CIRA, The Watchers. Acquired at 11:50 UTC on March 13, 2023