Two More Atmospheric Rivers are on Their Way to California

ON 01/23/2023 AT 08:48 AM

After previous waves delivered record-setting torrential rains to the west coast this past week, two more high-altitude rain chutes are scheduled to drench much of Northern California and parts of the southern region this weekend.

Croplands damaged by floods

The heavy rains which hit California over the last two weeks did substantial damage to agricultural lands which may take many months to recover from. Photo: Pfenning's Farm, via Twitter

Since the end of December, six “atmospheric rivers” have rocketed out from high above the central Pacific Ocean to blast across the California coast and created life-threatening floods from the north of San Francisco all the way to the state’s southern border. Together those storms have let loose trillions of gallons of rain on a state which just before they came was suffering the worst drought of this century and the last.

Such atmospheric rivers are formed by hot ocean waters, themselves a byproduct of global heating and the climate crisis, which throw up mist and vapor into the atmosphere, where they are caught by unusual wind and pressure patterns which draw them to high altitudes. That waterlogged air cools as it rises there, with thermals underneath keeping it suspended high above the ocean surface rather than allowing it to fall in the form of rain. That high density moisture is pushed forward by powerful global air currents such as the jet stream and other circulatory waves, which themselves are propelled in part because of the rotation of the earth and steered by different atmospheric pressure. The aerial rivers can travel thousands of miles before eventually falling, often catastrophically fast, as the wind and air pressure zones collide with others, often at the borders of large land masses.

This onslaught broke records for this kind of weather in almost every category imaginable. Since the storm pattern began:

Total California Rainfall Dec 24, 2022 to Jan 9, 2023

A map of the total rainfall accumulated in California since this wave of atmospheric rivers began last month. Photo: NWS Weather Prediction Center, via Twitter

Many areas have experienced up to 20 inches of rain, far higher than just about anything experienced in recent years, and certainly not on a statewide basis.

Multiple cities, particularly in the north central and San Francisco Bay area of the state, experienced over half their total annual rainfall in just a little over two weeks. Among those were Oakland with 69% of their yearly total; Santa Barbara, with 64% of its annual precipitation, where drain lines were so backed up that sewage flooded onto the city streets and walkways; Stockton with 60%; and downtown San Francisco, at 59% of annual average rainfall.

Oakland’s 16.10 inches of rain received since December 26 is 11 inches over the normal amount for this time of year. In the state capital of Sacramento, the 14.25 inches of rain it received is roughly 10 inches above normal levels.

There were 955 reports of flooding, “debris flow” events in which streaming surface water was moving so fast and deep that it was more of a slurry of vegetation and trash mixed with water than normal flooding, and flash floods.

The flooding is so severe that local officials along the northern California coast are not reporting the Monterey Bay peninsula could temporarily become an island, with no land-based means of leaving or coming to that area for at least days.

Flashfloods have also caused mud to spread across many roadways, forcing rerouting in many areas. As just one of many examples, mudflows resulting from the floods just shut down the connector from Interstate 5 to the 110 freeway at Elysian Park.

Wind, torrential rain, and flooding associated with the atmospheric river dumping caused power outages for almost 38,000 homes across the state.

Snowpack surged by over 10 feet in the highest – and previously bone-dry – parts of the Sierra Nevada Mountain range. Overall snowpack in the state as of now is 227% of normal for this early date in the year. While that is good, since that snowpack when it melts continues to refill reservoirs, lakes, and rivers much later, the current snowpack is still just 104% of the long-term typical snow accumulation by April 1. So even after all the rains to date, far more snow must still fall in the mountains to keep reserves high.

As of January 12, at least 19 people had died because of the storms. One of the most recent was a woman found inside a car forced fully underwater because of the floods in the city of Forestville, in the northern California country of Sonoma. As more cars are brought in from where they had been pushed away and down into the raging waters, more bodies are expected to be found.

Agricultural land damage and losses of already-planted crops are expected to be massive, when finally tallied. The impact will ripple across the country within months, as food shortages from this important vegetable and fruit growing region begin to grow.

Many homes, buildings, and other structures which were flooded out have also been badly harmed. Totals for this damage can only be completed once the current storms have eased and the true impacts can be properly determined.

One positive result of the statewide rainfall is that it has saved California for a short time from the widespread drought which has grown rapidly worse in recent years.

Drought eases in California after Atmospheric Rains

Drought is currently down substantially in California as a result of the current wave of severe rainstorms. Photo: U.S. Drought Monitor Service at the University of Nebraska-Lincoln

Thanks to the intense rains, for the first time since April 4, 2020, there were no parts of the state suffering from what is categorized as an “exceptional” drought. Official records also showed that only 0.32% of the state was in the next lower level of drought called “extreme” drought. That “dry patch” is present only in the northernmost part of the state, where the rains mostly missed the area.

Just one month ago, those numbers were vastly different, with 7% of California showing up in the exceptional drought category and 36% of the state in extreme drought.

Lake Shasta and Lake Oroville have also filled considerably in the last two weeks, to now 44% and 49% of total capapacity.

While the rainfall has helped fill rivers, lakes, and reservoirs again in the state, and drought levels are far less serious now, weather forecasters caution that the severe drought conditions could return as early as this summer. That is because even in normal years the rainy season for California typically ends in April. They also are reminding us now that a very rainy December 2021, which many thought would break the drought pattern for longer, ended up leading to the driest January-March period in the state’s history. That in turn led to last year eventually going down in the books as leading to the worst drought in the recent history of the state.

Scientists also note that the current rainfall has had almost no effect on the dangerously-low levels of water at Lake Mead and Lake Powell, the nation’s two largest reservoirs and which are fed by the Colorado River. So although California might be in better shape than just a few weeks ago, the heavy recent rainfall in the state will have little impact on the overall water problems of the other western states and Mexico which depend on the Colorado River for water.

The return of the drought will be postponed for a while further yet, despite all that, as at least two — and maybe three — atmospheric river rainfall events are scheduled to hit California between now and next week.

The first, which will begin to bring rainfall this weekend across the central and southern parts of the state, will, according to the National Weather Service, “still be [an] above-average winter storm but “considerably weaker” than the past ones. Wind speeds of up to 40 mph are expected in the counties of Santa Barbara and San Luis Obispo. It will move through quickly.

A second is expected to come immediately on the heels of this last one. It will travel more slowly so that although it is also expected to be less intense, more rain and flooding may come from this one. That second storm will also bring new snow to the state, with accumulations starting at the 6,000-foot level.

In addition to coping with severe drought, California and many other parts of the world must also adapt to extreme rainfall and be able to divert the floodwaters away from cities and farm fields and then capture the water for later use.