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L.A. had hotter-than-normal August and September

October 1, 2012 |  2:07 pm

Weather Story (click the image for a higher resolution image).

In two days, Southern Californians will get to celebrate “Good Wednesday.” No, it's not a religious event, but a day when the scorching, humid temperatures that have afflicted the region for the better part of two months give us a merciful break.

After near triple-digit temperatures in downtown Los Angeles, the middle of the city will see temperatures in the more tolerable mid-80s, with a deeper migration of sea breezes, said Ryan Kittell, a meteorologist for the National Weather Service in Oxnard. It’ll be a break from an August and September that largely flipped the script on a year that had actually been cooler than normal through July.

Bill Patzert, a climatologist for the Jet Propulsion Laboratory in La Canada-Flintridge, said that in the last three years summers, falls and springs had on the whole been cooler—and that applied to August and September, two traditionally very warm months.

“Then all of a sudden this August, we had a complete flip-flop,” he said. “It’s been hot and steamy.”

Until August, every month in 2012 except for January had been cooler than normal. Then August was more than 2 degrees hotter than average, and September more than 3 degrees.

On Monday, temperatures in L.A. danced around 100 degrees.  

Patzert said the last three years were dominated by cool ocean temperatures that blanketed much of the Southland in a marine layer.

But in the last two months, L.A. has been under the thrall of a high-pressure system parked just above us to the northeast. That has conspired with a low-pressure system just offshore to bring hot and muggy weather.

“You have the high-pressure system, where the air is circulating clockwise, and the low-pressure system, where it’s turning counterclockwise,” Patzert said. “So not only is it bringing us the warm air from the high desert, but the moist air from the Gulf of California and the Pacific.”

Though there should be a cool down beginning Wednesday, October, like September, is generally also a heat-wave month. It also marks the beginning of the Santa Ana wind season.

That could bode ill for the risk of wildfires, particularly with the lack of precipitation. While L.A. has experienced a few sizable brush fires this summer, they’ve been largely controllable because of the lack of strong winds.

That could change, Patzert said.

“It’s very crispy out there, and we’ve had some fires, but the one missing ingredient was we haven’t had any wind,” he said. “When you look down into the tunnel here, we’re definitely looking at the Santa Ana season coming up. So the situation could be incendiary.”

The National Weather Service is forecasting a “weak to moderate” El Nino, which could mean a “little better chance than normal” of rain, Kittell said.

He said there are already signs of warming ocean temperatures in the central Pacific, a sign of an impending El Nino, though Kittell noted that’s not “necessarily a slam dunk” for  a wet winter.

But Patzert said that he doesn’t think the El Nino will materialize. Rather, he thinks Southern California is headed for what he called “La Nada.”

And that means unpredictability, he said.

“It’s pretty hard to forecast when you don’t have an El Nino or La Nina. You’re kind of adrift,” Patzert said. “We’ve had the driest winter and the wettest winter in conditions similar to what we have now.”

Given the face-peeling heat, it’s probably a safe bet most people are rooting for the relief of the latter.

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--Hector Becerra

Image: National Weather Service

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