This week’s heatwave broke records, but there’s relief in sight

Rest easy, Southern California, there’s an end in sight to this week’s record-breaking heatwave.

Downtown Los Angeles broke its daily record Monday at 98 degrees, and tied it two other times in the last week.

Woodland Hills hit 111 degrees on Wednesday, breaking its daily record of 109 degrees. Lancaster hit 107 degrees, breaking its record of 106.

Humidity was also unprecedented. The dewpoint, essentially a baseline of how much moisture can be held in the air, reached nearly 73 degrees in downtown L.A. on Thursday. Dewpoints over 70 degrees typically feel uncomfortably humid.

Parts of Southern California farther inland, near the Salton Sea, had some of the highest dewpoints in the country.

Extreme heat warnings from the National Weather Service were scheduled to remain in place for most of the region through Friday evening.

Officials say the conditions pose a high risk of heat-related illness for most people. Sensitive groups are especially susceptible, including people over 65, young children, people without access to air conditioning or those who work outdoors.

Fire danger is also elevated. Red flag warnings are in effect until Friday at 3 p.m. for the inland mountains and foothills of L.A., Ventura and Santa Barbara counties, although there is fire risk across the region.

The good news is forecasters predict a cooldown Saturday.

“We'll drop our high temperatures fairly noticeably each day through the weekend and early next week,” said NWS meteorologist  Rose Schoenfeld. “Early next week we'll end up closer to normal, maybe even a little bit below normal.”

Humidity vs. fire danger

Abnormally high humidity in the region continues to make this week’s heatwave feel even more uncomfortable.

The moisture also brought cloud cover, and in places, even a chance of light showers and thunderstorms.

But there isn’t enough moisture in the air to put a damper on fire conditions. Without significant rain, thunderstorms can create dry lighting, which can spark wildfires.

“Fire and thunderstorms can be linked together, but mostly it's because it's very hot and the atmosphere is primed for plume-dominated fire development,” Schoenfeld said.

More concerning to forecasters is the combination of high temperatures and gusty winds, especially inland and at higher elevations. If a fire does start under those conditions, it can spread quickly.

A 'confluence' of factors

The temperature of the ocean has a lot to do with the heat and humidity.

Normally, the Pacific Ocean acts as air conditioning for Southern California by cooling the air that moves inland.

But waters off the coast of California and Mexico have been experiencing a long-term marine heatwave for more than a year, and warm surface temperatures have reduced the natural cooling effect.

Ocean temperatures are also driving up the humidity. Seawater evaporates faster when it’s warmer, adding moisture to the air.

At the same time, farther away in the Pacific, warming waters closer to the equator are leading to tropical storms and cyclones. As the storms dissipate, they send moisture all the way here.

Scientists say warming in the equatorial Pacific is one of the early impacts of this year’s El Niño.

"It's the confluence of this somewhat unusual weather pattern with these very unusual temperatures off the coast of Baja and Southern California, layered onto a warmer world,” said Alex Hall, a professor of atmospheric and oceanic sciences at UCLA. “That's what's making this such an extreme event.”

Hall said climate change is making heat waves worse by elevating baseline temperatures, which drives longer stretches of uncomfortably or even dangerously hot days, and warmer nights that provide less relief from the heat.