A storm system arriving during the second half of next week has the potential to bring widespread moderate to heavy rainfall to Southern California, the National Weather Service said.
Rainfall figures can sometimes be high, increasing the possibility of litter flow in recent fire areas, as well as mud and rock slides on mountain roads. Significant snow accumulations are possible with the storm, mainly more than 5,000 feet.
The biggest storm, the third in a series, is predicted to include an atmospheric river. Atmospheric rivers are a concentrated stream of water vapor in the middle and lower levels of the atmosphere. Because they are less in the atmosphere, they tend to be warmer, even if they do not lead directly to the tropics.
This atmospheric river will come more from the west, said Eric Boldt, a meteorologist for warning coordination at the National Weather Service in Oxnard. ‘It’s not a direct tropical connection, but [has] above-normal water content that can bring moderate hours of rain. ”
It is predicted that an atmospheric river will accompany the most powerful in a series of three storms hitting the South by the end of the week.
(Paul Duginski / Los Angeles Times)
The pattern change comes after a summer with record heat, the worst fire season in California history and a dry fall and early winter raked by Santa Ana winds.
After a hot summer, the entire state was extremely dry during the fall and early winter.
(Paul Duginski / Los Angeles Times)
Although the northwestern and northern Intermountain West in the Pacific Ocean has suffered heavy rainfall due to a series of storms in the North Pacific, the central and southern parts of the West are in drought that is as severe as it can get. As areas already classified in the extreme and extreme drought, “not much deterioration can occur,” the U.S. drought monitor reported Thursday.
A wetter pattern will provide welcome relief in the South West, which has been dried up by prolonged drought. The latest data from the US drought monitor was released on Thursday.
(Paul Duginski / Los Angeles Times)
About the only way such a dehydrated, scorched landscape can get worse is to release heavy rain from an atmospheric river – rain that is like a fire hose – washing mud and debris into rugged slopes. Rain is needed, but not all at once. If heavy rains occur, there is a risk of debris flowing in recent burns such as those left by the Lake, Bobcat and Ranch2 fires, and other fires in Orange County and the Inland Empire.
Forecasters do not expect an epic rain scenario, but warn that the public should pay attention to updates and follow the directions of the authorities if they are told to evacuate.
Large amounts of rain are not necessary to create a dangerous situation. The mudslide from Montecito in Santa Barbara County on January 9, 2018, following the Thomas fire, for example, occurred just after half an inch of rain. But the rain fell in about five minutes, yielding the waste that was 15 feet high.
One decent storm in December marked an otherwise dry fall and early winter in downtown Los Angeles.
(Paul Duginski / Los Angeles Times)
How did we get to this point?
A La Niña is in the equatorial Pacific Ocean and is expected to continue through the rest of the winter. La Niña usually leads to a dry winter in Southern California and the Southwest, although this is not always the case. El Niño, the wetter cousin of La Niña, usually means a wet winter in Southern California, based on history, but again, there are no guarantees.
The South has experienced one storm over the past nine months, and the dry pattern so far has been in line with a typical La Niña winter – which is also usually wetter than normal in the Northwest Pacific and across the Northern Tier United State.
Although the Los Angeles region had near-normal rainfall last winter, the excessive summer heat and dry winds of Santa Ana caused the fuel to burn in the fall and early winter. Numerous major fires burned more than 4 million acres in California by 2020, sometimes enveloping almost the entire state in smoke.
In a Mediterranean climate like California, rain usually falls during the winter. Even without the influence of El Niño and La Niña, Southern California is dependent on five to seven significant storms for its rainfall each year.
“In LA, it does not rain or drip every day during the winter like in Seattle,” said climatologist Bill Patzert. ‘Rain occurs on five, six or seven occasions. There is usually less than 20 days of rain and less than ten days of rain throughout the season. ”
The Los Angeles Basin is a floodplain. After a season that began to dry up in 1937-38, two storms in late February and early March 1938 suddenly dropped as much rain in the region in five days as usually falls in an entire season. Catastrophic floods from the foothills to Long Beach followed, causing an amount of billions of dollars in damage in today’s dollars. Angelenos was fed up with such recurring, damaging floods. These events eventually prompted authorities to tame the Los Angeles River and other waterways by covering them with concrete for flood control.
As Patzert noted, these concrete channels do not flow on a large scale about 99% of the time.
A reminder of what may have happened before these waterways were made in concrete canals took place on New Year’s Day in 1934.
In November 1933, a fire denied an area of 7.5 square kilometers to the foothills above Montrose and La Crescenta. On December 31, 1933 and January 1, 1934, an atmospheric river storm dropped 10 to 15 centimeters of rain on congregations at the foothills and as much as 20 to 30 centimeters on the foothills and mountains. Downtown Los Angeles received 8.27 inches of rain, according to The Times.
The deadly New Year’s flood was front-page news in the Los Angeles Times.
(Los Angeles Times)
“The flood in Montrose, as the disaster is soon called, took at least 45 lives, destroyed about 100 homes and transformed the small community into a muddy, arid landscape,” said local historian Art Cobery. the catastrophe and its aftermath, ”The Times reported in 2009.
After the 1934 New Year’s Flood in Los Angeles, cars were created in mud outside the Bohemian Gardens on Mission Road. One man lost his life there.
(Los Angeles Times)
Singer-songwriter Woody Guthrie commemorated the tragedy in a song about the Los Angeles New Year’s Flood.
Atmospheric rivers are extremely wet plumes of moisture. They can drop rain in the countryside when they come ashore, but when they lift up and over the steep and rugged coastal hills and mountains, their load of moisture is drawn out. This means that they are dropping heavy rain, possibly at an intense pace, on the areas deprived by veld fires this past summer and autumn.
‘This all serves as a warning to those living under fire areas, such as the Bobcat fire in the San Gabriel Mountains. “Mud spills can not be predicted, but they can be predicted,” said Patzert. “The best protection against mudslides is to stay informed and evacuate when authorities issue warnings.
“Great droughts, fires, floods and mudslides after heavy rains, decade after decade. It is a story that has been told for thousands of years, ”Patzert added. “It’s a classic in California.”