“Exceptionally” dry conditions in Los Angeles make the risk of new fires high. urgent need for rain

Winds are expected to continue to dissipate this week, but that will be a brief respite for fire-stricken Southern California.

There is an increasing risk of significant fire weather again in Los Angeles and Ventura counties starting early next week.

But in addition to wind, the region is also at risk of extreme dryness and lack of rain.

Southern California is experiencing one of its driest winters on record. Alex Tardy, a meteorologist with the National Weather Service’s San Diego office, said the water year, which began on Oct. 1, saw only 5% of the average rainfall in much of the region. % or less.

Since October 1, downtown Los Angeles has received just 0.16 inches of rain, just 3 percent of the 5.56 inches average for this time of the season.

According to data shared by Tardy, the lowest record for this 3.5-month period in downtown Los Angeles was the water year that began on October 1, 1903, with no trace of rainfall detected until January 13, 1904.

The early part of the 1962-63 water year was also very dry, with only 0.16 inches of rain falling in downtown Los Angeles by January 13, 1963.

The average annual rainfall in downtown Los Angeles is 14.25 inches.

For many other areas in Southern California, “it’s the driest start of any water year,” Tardy said, “and you can see extreme fire behavior when it comes to ignition.”

In San Diego, only 0.14 inches of rain fell between October 1 and January 14. The previous record for this period was 0.35 inches of rainfall accumulated between Oct. 1, 1962, and Jan. 14, 1963, according to National Weather Service forecaster Miguel Miller in San Diego.

Exacerbating fire weather conditions, January is peak Santa Ana wind month, which creates strong winds when high pressure over Nevada and Utah pushes cold air toward low-pressure areas along the California coast.

As air flows from the high desert (from the Northeast) down through California’s mountains and canyons, it becomes dry, compressed, and warmed, and as the wind blows, so does the vegetation.

Santa Ana winds are typically strongest in January, Tardy said, citing research from the U.S. Forest Service and Scripps Institution of Oceanography.

“Santa Ana is very common in December and January, and typically that’s when we see the strongest, largest and most destructive storms. But we don’t have those normal dry conditions,” Tardy said.

“In my career, I have never seen a Santa Ana event so severely overwhelm the normal winter rainy season,” said retired climatologist Bill Pazett.

The next few days, Monday and Tuesday, are the most concerning, with a 70 percent chance of a red flag warning in Los Angeles and Ventura counties, indicating a high likelihood of severe fires should they break out, according to the National Weather Service. .

“The bottom line is that all of next week looks very dry, with an increasing risk of a red flag warning being issued,” said Ryan Kittell, a meteorologist with the Oxnard weather service office.

Relative humidity may drop below 10% next week, meaning vegetation will be particularly dry and fragile.

“It seems almost beyond expectations,” Kittle said.

As for wind energy, there is growing confidence that mild wind energy will be developed in St. Anas. As of Wednesday, forecasters estimated a 70% chance of moderate Santa Ana winds on Monday and Tuesday. The day before, the chance was 40%.

The chance of strong Santa Ana winds remains low.

Winds next week are expected to be affected by the “Inner Slider,” a low-pressure system expected to move down from Canada into California and Nevada and bring winds from high pressure to the Great Basin, but There will be no urgent need for rain.

The system is called an “internal slider” because “it just slides inside and never goes over the water and doesn’t give us a chance of rain,” Kittle said.

High pressure that will deliver cold, dry air to Southern California next week is also being influenced by cold air expected to move from the Arctic into the northeastern United States, Tardy said. “We’re going to be on the windy, dry side of the cold air.”

That means “we’re just going back to the same pattern,” he said.

“This is truly a record that has been broken. Although Santa Ana winds are common and normal this time of year, it is not normal to be this dry,” Tardy said. “Typically, between Santa Ana, you get at least one rainfall and a Pacific storm every year on average, and we didn’t even see that.”

Before winds pick up next week, there will be a few days of relief from the severe fire weather that leveled devastating fires in and around Altadena and Pacific Palisades.

“So the moral of the story is, thankfully we’re going to get out of this this weekend, but unfortunately it’s going to be short-lived,” Kittel said of the dangerous fire weather.

For now, forecasters don’t expect to issue extreme hazard warnings, known as “particularly hazardous conditions,” next week.

“But it’s still something we’ll be watching closely,” Kittle said.

This week’s extreme red flag fire weather in the San Fernando Valley, large swathes of Ventura County and the Grapevine stretch of Interstate 5 peaked around noon Wednesday and ended at 3 p.m.

Wind gusts in excess of 30 mph were reported early Wednesday afternoon along the traditional Santa Ana wind corridor and extending southwest through Palmdale, Santa Clarita, Ventura, Oxnard, Simi Valley and Thousand Oaks, among other places.

Winds on Wednesday were about as expected, but winds on Tuesday were less severe than expected. One potential reason, Kittel said, is that the pressure difference between the ocean and the desert isn’t as great as the computers predicted.

Another possible reason, Kittle said, is that a low-pressure system spinning off the coast where Santa Ana winds travel westward is swinging farther north than expected.

This low-pressure system, isolated from the main jet stream and known as a “cutoff low,” can swing from side to side and be less predictable than when the system is connected to the jet stream.

Cutoff lows are so notorious for forecasters that they’ve been called the “weatherman’s scourge,” Kittel said.

Most of the red flag warnings for a large swath of Southern California expired at 6 p.m. Wednesday, including Los Angeles, San Diego, Orange, Riverside, San Bernardino and Ventura counties, as well as Santa Barbara. The mountainous areas of Barra and San Luis Obispo counties.

As of 3 p.m. Thursday, a red flag warning will remain in place for a small portion of Los Angeles and Ventura counties, including the Grapevine section of Interstate 5, the western San Gabriel Mountains and the Santa Susana Mountains.

Dry air will persist Thursday, with relative humidity between 8% and 20% fairly common in Los Angeles and Ventura counties and surrounding areas. Temperatures will still be much cooler than normal in Redondo Beach, Thousand Oaks and Oxnard, with Friday’s high (the coldest day of the next few days) reaching just 58 degrees; in downtown Los Angeles, Long Beach and Covey Na 59; Canoga Park Route 60; Santa Clarita 61.

“The upside to our weather concerns is that humidity will continue to climb, especially in [Thursday]reducing fire weather concerns,” Kittle said. As humidity increases Friday and Saturday, fire weather concerns should be fairly minimal, although localized wind gusts of 25 mph to 40 mph are possible from the northwest.

Kittle said a low-pressure system off the Southern California coast will move in, but there’s a slim chance of rain Saturday night into Sunday.

“It will eventually move ashore and all forecasts keep it south of Los Angeles County, so the chance of rain is very slim,” Kittle said.

Southern California won’t be much safer from wildfires until there’s lots of rain. Forecasters say the chance of rainfall remains low through January 25.