The arrival of a strong atmospheric river next week will raise the risk, possibly leading to debris flow and rain that could cause landslides in burned areas in Los Angeles County.
There is currently a 30% chance of rain falling from February 12th to 15th in Los Angeles, Ventura, Santa Barbara and San Luis Obispo counties. .
The current chances of moderate or low rain are 30%, and the chances of not raining are 10%.
“The scope of the results is still very uncertain, but the possibilities for a powerful, very wet system are still there,” said meteorologist Ryan Kittel at the National Weather Service office in Oxnard. .
One reason these predictions are concerned is that the likelihood of heavy rainfall is usually low. “This risk is definitely higher than most of our storms,” Kittel said.
(National Weather Service)
A high-speed scenario can mean a heavy rainfall rate of 0.5 inches to 1 inch or more per hour. Speeds of more than 0.5 inches per hour can cause debris flow and landslides in recently burned areas.
Under this scenario, rain can arrive in slow moving storms that last within 12-24 hours, potentially being dumped over 2-4 inches on the coast and valleys and over 4-8 inches in mountains and hills.
As a result, there is a high risk of flooding and debris flowing,” Kittel said. “Again, that’s not the most likely outcome, but it’s a much higher risk compared to a normal storm.”
Recently burned areas are at risk of landslides in heavy rain, and the soil is no longer anchored by healthy vegetation. The worsening of the problem is that heat from the fire makes it difficult for the soil to absorb water, and the ash tends to clog the soil.
As a result, water can start to flow downhill soil surfaces. It can cause mud flow. There, water runs over just the flow of mud and more serious debris, while water picks up rocks, branches and sometimes huge rocks, moving at speeds above 35 mph. Both mudflows and debris flows are considered types of landslides.
Animated infographics show that shard flow works
Heavy rain could be “a bad, serious debris flow that causes deep currents that affect roads and even structures.”
One of the worst debris streams in modern California history came in January 2018 when a river of mud and rock flowed through Montecito, killing 23 people and destroying at least 130 homes. The area was burned a month ago by the Thomas fire. One of California’s most destructive records, its flames burned 282,000 acres in Ventura and Santa Barbara counties, destroying more than 1,000 structures.
A contribution to the severity of the Montecito debris flow was that government officials were unable to build a larger basin that could not be devastating or devastating. The report also found that Santa Barbara County failed to completely empty existing basins prior to disasters, significantly reducing its ability to trap debris.
The Times investigation shows that county flood management personnel and the Army Corps of Engineers have been getting too few catchments for half a century, and what they had too small, making it a huge remnant that makes it easy for Santa Inez mountains to live in. I knew it was too small to stop. To produce.
The Times also discovered that Santa Barbara County issued conflicting evacuation orders leaving the most intense neighborhoods from the forced evacuation zone. We didn’t send Amber Alert Style breaking news to our mobile phones until the landslide began. By then it was too late for residents to escape.
Possible storms before or around Valentine’s Day is raining in Southern California, resulting in weak atmospheric river storms. The storm was expected to peak in Los Angeles County between Thursday evening and noon Friday.
Additional rainfall is expected on Thursday and Friday.
(National Weather Service)
From the current storm, Long Beach and Redondo Beach were able to get a third of the rain. Thousand Oaks and Oxnard, two-fifths of an inch. Santa Clarita and Canoga Park, about 0.5 inches. San Luis Obispo, 2/3 inch. Downtown Los Angeles, Covina, Fillmore, 1/7 of 16 inches. Santa Barbara, about 1 inch. Ojai, about 1½ inch.
The storm is likely to be “generally beneficial,” with only slight road flooding expected, and perhaps mud and rock could fall onto the canyon road, Kittel said. There is only a 5% to 10% chance of a thunderstorm.
Rain in the Pallisard and Etonburn areas could fall by half the rate from a quarter per hour. This is below the threshold where rainfall is expected to spur serious debris flow and landslides.
“What we’re trying to see is probably a little mud and dirty water that flows through some roads, but… there’s a very small impact,” Kittel said. “There will be something that will flow down the burn scars that could affect some local roads.”
The risk of a significant debris flow on Friday was low, below 10%, Kittel said. This can occur when cells from enhanced storms, such as thunderstorms, happen to go directly above the burns. “It’s kind of like throwing a coin into a big pond and trying to hit a fish,” Kittel said. “It’s not zero, but it can happen.”
The current storm is expected to bring gusts of wind from 20 mph from the south to downtown Los Angeles and Long Beach, rising to 30 mph at Thousand Oaks, Santa Clarita and Santa Barbara, and rise more than 40 miles per hour in the high deserts of LA County I did. In San Luis Obispo County.
Starting Friday night, dry winds are expected to arrive from the northwest and northeast, and continue until Monday. Downtown LA and Long Beach were able to see gusts of winds of about 14 mph. Thousand Oaks and Canoga Park, 21 mph. Santa Clarita, 26 mph. Lancaster, 37 mph; Pyramid Lake, 45 mph. Fire weather conditions are expected to be minimal due to recent rain.
However, LA was not expected to rain enough this week to clearly declare the end of the fire season. A few weeks of dry weather return may be enough to bring the area back to the risk of dangerous fire weather conditions, especially if the winds return in Santa Ana. Severe Santa Ana winds are most common from October to March and can occur by May.
Downtown LA has received just 1.02 inches of rain since the year of water began on October 1st. The average for this period – just over four months from the year of water – is 7.8 inches. The average annual average is 14.25 inches.
Downtown’s driest water year on record ended September 30, 2007. A bad fire season continued. The biggest flames burned 240,000 acres in Santa Barbara County, nearly 198,000 acres, destroyed 1,650 acres and killed two people in San Diego County.
Despite the rain, Southern California’s drought conditions have worsened for another week, and are now considered to be in a “extreme drought” state, with only the second worst category tracked by the US Drought Mitigation Center. there was.
The latest map of the Center, released Thursday, shows almost everything in Southern California, including most of Los Angeles and Ventura counties, as well as all of Orange and San Diego counties, in “extreme droughts.” Much of the rest of the area is believed to be in severe drought.
The rain doesn’t provide enough water to stop the drought situation, said Lindsay Johnson, the center’s climatologist who wrote the latest map. She said the Center’s analysis not only takes into account rainfall, but also soil moisture, snowmen, fire hazards and other hydrological metrics.
“The longer the dry times, the more generally speaking it will rain to return to normal,” Johnson said. “There’s a lot of deficits to make up for it.”
Heavy rains in the northern part of the state have led authorities to begin releasing water from Shasta Dam into the Sacramento River. Two other reservoirs are also releasing water, the Reclamation Bureau announced Thursday.
Lake Shasta, California’s largest reservoir, has risen over 22 feet since January 31st.
“At the same time, Sacramento’s federal pump at Joaquin Bay Delta is currently operating at its maximum capacity, storing water in the San Luis Reservoir, and south to farms, communities and wildlife shelters if needed later this year. “We support delivery.” The agency wrote in a news release.
Lake Shasta is 134% of the historic average of this period.
Lake Oroville – The keystone of the National Water Project, which supplies water to the state’s second largest reservoir and the San Joaquin Valley and the San Francisco Gulf region, is 137% of the historic average.
San Luis Reservoir, California’s fifth largest reservoir, is 121% of its historic average. Mercedo County reservoirs store water from the Joaquin River Delta in Sacramento and San, and are later delivered to Southern California, the San Joaquin Valley, the Central Coast and Silicon Valley.
North Sierra has accumulated 37.4 inches of precipitation since the Wednesday fiscal year began on October 1st. This is 128% of the average at this point in the season. A few months.
Times staff writer Ian James contributed to this report.
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