L.A.’s ‘off the charts’ dryness keeps risk of new fires high. Rain is desperately needed

Winds are expected to continue dissipating this week, but it’s shaping up to be a short reprieve for fire-scarred Southern California.

There’s a growing risk that significant fire weather could return in Los Angeles and Ventura counties starting early next week.

But even more than winds, the region faces danger from extreme dry conditions and lack of rain.

Southern California is seeing one of its driest starts to a winter on record. Much of the region has received just 5% or less of its average rainfall for this point in the water year, which began Oct. 1, said Alex Tardy, a meteorologist with the National Weather Service office in San Diego, which also issues forecasts for Orange County and the Inland Empire.

Downtown L.A. has received just 0.16 of an inch of rain since Oct. 1 — 3% of the average at this point in the season, which is 5.56 inches.

The record low for this 3½-month time period in downtown L.A. was for the water year that began on Oct. 1, 1903 — when only a trace of rain was detected through Jan. 13, 1904, according to data shared by Tardy.

The early part of the 1962-63 water year was also very dry, with downtown L.A. receiving only 0.16 of an inch of rain by Jan. 13, 1963.

Downtown L.A.’s annual average rainfall is 14.25 inches.

For many other areas of Southern California, “this is the driest start to any water year,” Tardy said, “and you can see extreme fire behavior with the ignitions.”

In San Diego, just 0.14 of an inch of rain has fallen between Oct. 1 and Jan. 14. That’s the driest start to the water year in 174 years of record keeping. The previous record for that time period was 0.35 inches of rain that accumulated between Oct. 1, 1962 until Jan. 14, 1963, according to Miguel Miller, forecaster for the National Weather Service office in San Diego.

Exacerbating the fire weather situation is that January is the peak month for Santa Ana winds — powerful winds that develop when high pressure over Nevada and Utah sends cold air screaming toward lower pressure areas along the California coast.

The air dries out and compresses and heats up as it flows downslope from the high deserts — from the northeast — over California’s mountains and through canyons, drying out vegetation as the wind gusts through.

The magnitude of Santa Ana winds is typically strongest in January, said Tardy, citing research by the U.S. Forest Service and the Scripps Institution of Oceanography.

“Santa Anas are very common in December, January, and that’s usually when we see our strongest and biggest and most damaging ones. But we don’t have conditions this dry normally,” Tardy said.

“During my career, I’ve never seen punishing Santa Ana events so overwhelm the normal winter rain season,” said retired climatologist Bill Patzert.

In the coming days, Monday and Tuesday are of the most concern at this point, with a 70% chance of red flag warnings for Los Angeles and Ventura counties, which indicates a high likelihood of critical fire behavior should one ignite, according to the National Weather Service.

“The big story is that it just looks very dry all week next week, with a growing risk of red flag warnings,” said Ryan Kittell, a meteorologist with the weather service’s office in Oxnard.

Relative humidity could fall under 10% next week, meaning vegetation will be especially bone dry and vulnerable.

“It just almost looks off the charts,” Kittell said.

As for wind, there is increasing confidence that moderate Santa Anas will develop. As of Wednesday, forecasters estimated the likelihood of a moderate Santa Ana wind event at 70% for Monday and Tuesday. The day before, the probability was pegged at 40%.

There is also still a small chance of a strong Santa Ana wind event.

The winds next week are expected to be influenced by an “inside slider” — a type of low-pressure system that is expected to move down from Canada into interior California and Nevada and bring wind from high pressure over the Great Basin, but not the rain that is desperately needed.

The system is called an “inside slider” because “it just slides inside, never goes over water, never give us that chance for rain,” Kittell said.

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

It’ll mean “we just go back into the same, same pattern,” he said.

“It’s really been a broken record. Even though Santa Ana winds are common and normal this time of year, it’s not normal to be this dry,” Tardy said. “Normally, in between Santa Anas you’ll at least get a rain and a Pacific storm in an average year, and we’re not even seeing that.”

Before next week’s winds pick up, there will be a few days of a welcome break from severe fire weather after devastating fires that flattened large areas in and around Altadena and Pacific Palisades.

“So the moral of the story is we are, thankfully, going to get a break from all this for the end of this week, but unfortunately, it’s going to be short-lived,” Kittell said of dangerous fire weather.

For now, forecasters don’t expect to issue an alert indicating an extreme red flag warning next week, known as a “particularly dangerous situation.”

“But it’s still something we’ll keep an eye on,” Kittell said.

As for this week, a “particularly dangerous situation” of extreme red flag fire weather peaked around midday Wednesday for the San Fernando Valley, swaths of Ventura County and the Grapevine section of Interstate 5, and it expired at 3 p.m.

Gusts of more than 30 mph were seen early Wednesday afternoon along a traditional Santa Ana wind corridor, stretching southwest through places including Palmdale, Santa Clarita, Ventura, Oxnard, Simi Valley and Thousand Oaks.

Winds on Wednesday were about as expected, but Tuesday’s winds were less severe than had been anticipated for that day. One potential reason is that the difference in pressure between the ocean and deserts wasn’t as strong as the computers projected, Kittell said.

Another possible reason is that the low-pressure system spinning off the coast — where the westward Santa Ana winds are traveling — wobbled a little bit farther to the north than expected, Kittell said.

Cut off from the prevailing jet stream, that low-pressure system is something called a “cutoff low,” which wobbles around and can be less predictable than if the system were connected to the jet stream.

Cutoff lows are so notorious to forecasters that they’re referred to as “weatherman’s woe,” Kittell said.

Red flag warnings for swaths of Southern California mostly expired at 6 p.m. Wednesday, which had affected areas in Los Angeles, San Diego, Orange, Riverside, San Bernardino and Ventura counties, as well as the mountains of Santa Barbara and San Luis Obispo counties.

A red flag warning will remain in effect for a smaller portion of L.A. and Ventura counties through 3 p.m. Thursday, including the Grapevine section of Interstate 5, the western San Gabriel Mountains and the Santa Susana Mountains.

There will be lingering dry air through Thursday, with relative humidity between 8% and 20% fairly common in and around Los Angeles and Ventura counties. Temperatures will remain much cooler than normal, with highs on Friday — the coldest of the next few days — reaching only 58 degrees in Redondo Beach, Thousand Oaks and Oxnard; 59 in downtown L.A., Long Beach and Covina; 60 in Canoga Park; and 61 in Santa Clarita.

“On the good side for our weather concerns, humidities will continue to climb, especially after [Thursday], with lowering fire weather concerns,” Kittell said. With increasing humidity on Friday and Saturday, there should be fairly minimal fire weather concerns, although there could be localized gusts of between 25 mph and 40 mph from the northwest.

The low-pressure system sitting off the Southern California coast will move, but there is only a scant chance of rain Saturday night into Sunday, Kittell said.

“It will eventually move ashore, and all the projections keep it fairly south of Los Angeles County,” Kittell said, “so the chance of rain is very minimal.”

Southern California won’t be much safer from wildfire until plenty of rain falls. There are still no significant chances of rain through Jan. 25, forecasters say.