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Another atmospheric river is slamming California

Earth seen from space, there are white clouds over California.
This image from the GOES-18 satellite shows the latest atmospheric river on March 13, 2023, about to make landfall on the West Coast of the U.S. The storm is poised to produce more soaking rainfall in parts of the already-soaked state. Authorities expect widespread flooding. Image via CIRA/ CSU & NOAA.

Meteorologists: Storm to ‘hammer’ soaked state

Another warm atmospheric river is poised to dump several inches of rain – more than 6 inches (15 cm) in some areas – onto California’s already sodden landscape. The peak of the event is expected today, Tuesday, March 14, 2023, and will continue into Wednesday, March 15. This storm comes on the heels of an earlier storm, which produced prolonged, excessive rainfall over the weekend.

The National Weather Service (NWS) offered more dire predictions yesterday evening:

The environment will be very favorable for prolonged, terrain-enhanced rainfall along the central and southern coastline and the Sierra foothills. The global guidance and a majority of the hi-res guidance hammer this part of the state with 3 to 6+ inches of rain, some occurring over areas still dealing with the high stream flows of the previous, not-so-distant atmospheric river event.

Worse still, the NWS said the storm will melt some of the record amount of snow blanketing the Sierra:

Higher dew points are expected to infiltrate the region which will help prime the snowpack for melting and possibly expedited by the heavy rain, thus increasing the threat for rapid runoff and the areal coverage of flooding.

The NWS expects the latest atmospheric river event to stretch into tomorrow, Wednesday, March 15. Excessive rain will also move eastward across the U.S. and could also become a problem for parts of Arizona.

Meanwhile, meteorologists are discussing a system of intensity rankings for atmospheric rivers, similar to that for hurricanes. They are saying they hope the rankings will help keep people aware, and safe.

Foothills, interior flooding expected

As of late in the day on March 13, some parts of California were under mandatory evacuation orders, in anticipation of the coming storm, with FEMA urging residents to pay attention. Meanwhile, 40 of California’s 58 counties had already declared a state of emergency.

Extensive damage was caused by the weekend’s atmospheric-river-driven storm. Damage included a washed-out levee, a minor tornado and extensive, widespread flooding, the Sacramento Bee reported. The paper described the expected impact of the coming storm around the capital city and across the northern half of the state:

But virtually all of interior Northern California is again under a flood watch by the weather service due to this week’s incoming atmospheric river. Parts of the Sacramento Valley could receive up to 3 inches of rain from Monday night through Tuesday night, with as much as 7 inches possible in parts of the foothills.

The California Nevada River Forecast Center shows 16 rivers and creeks will rise above flood level, as of 12 a.m. PT (07:00 UTC) today, March 14. Most are located in the Sacramento and San Joaquin valleys. Thirty-four more waterways – stretching from the Oregon border to Mexico – are expected to rise above monitor stage.

Growing snowpack could mean weeks of flooding

Climate scientist Daniel Swain said the storm that hit California during the weekend acted to increase the Sierra snowpack.

The added depth means the state has more snow piled in its mountain ranges than ever previously recorded:

Swain warned that the weekend storm, despite its warmth, will likely add to those totals:

And that could lead to severe flooding for weeks to come, starting perhaps as soon as the end of March.

Atmospheric river: Orbital view of clouds streaming over Pacific Ocean onto U.S. West Coast.
An atmospheric river struck California on Friday, March 10, 2023. The system brought dangerous amounts of rain to the state, which continued into early this week. Plus, a 2nd atmospheric river struck the state, beginning yesterday, Monday 13. Image via CIRA/ CSU/ NOAA/ NESDIS.

Storms already turned deadly

An earlier atmospheric river had slammed California and the West Coast on Friday (March 10, 2023), with nearly the entire state experiencing “a dangerous rainfall event.” Already inundated from weeks of rainfall and snowfall, California underwent flooding over the weekend, as rivers overflowed their banks and poured into low-lying areas. At least two deaths occurred due to the flooding. And several communities were isolated.

Forecast updates and damage reports from all corners of the state filled social media.

What we’ve seen so far

Urban areas and highways also impacted by atmospheric river

Foothills of Central Sierra Nevada hit hard

In Sequoia National Park

Rain-soaked coastal regions inundated

In Santa Cruz County, San Lorenzo River topped its banks

Bottom line: Another atmospheric river will slam California today, March 14, 2023, bringing dangerous rainfall amounts and additional flooding. Look here for social media posts documenting the event.

March 14, 2023

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