Tuesday, May 20, 2025

Heat Wave to Bake Southern California, Relief Expected by Weekend

Temperatures to soar up to 18 degrees above normal before cooling trend begins Friday

A ridge of high pressure will bring dangerous heat to Southern California this week with temperatures peaking Wednesday and Thursday before a significant cooldown arrives for the weekend, National Weather Service forecasters said Tuesday.

Temperatures will climb 12 to 18 degrees above normal midweek, potentially reaching 100 degrees in the warmest valley locations, according to the weather service’s Los Angeles/Oxnard office.

“People working or playing outside in the valleys today should take heat-related precautions,” forecasters warned in their morning bulletin.

The heat wave intensifies Wednesday with highs reaching the 70s at beaches, 80s in inland coastal areas and 90s across the valleys. Weather service meteorologists said there’s a 40% chance that the warmest valley locations will hit 100 or 101 degrees.

Unusually warm overnight temperatures will compound the heat danger, with valley locations experiencing above-normal lows that will “exacerbate the heat danger,” the weather service said.

Heat advisories have been issued for much of the region away from the immediate coast. Details about heat precautions can be found in the National Weather Service’s hazardous weather outlook.

Some relief will begin Thursday as a trough moves through the Pacific Northwest, flattening the high pressure ridge. Morning fog and low clouds are expected along Los Angeles and Ventura County beaches Thursday, with a stronger afternoon sea breeze bringing “some late afternoon cooling relief,” forecasters said.

More significant cooling arrives Friday as a small trough pushes through the state, lowering temperatures 4 to 8 degrees along the coast and valleys. The marine layer will deepen enough to push cooler air into some valley locations.

The cooldown accelerates Saturday with valleys experiencing an additional 5 to 10 degrees of cooling, bringing temperatures down to near-normal levels in the 70s and low 80s.

“All of this cooling will bring maximum temperatures across the coasts and valleys down into the 70s with just a few 80 or 81 degree readings in the warmest valley locations,” the weather service said. “These maximum temperatures are within a degree or two of normal.”

Temperatures will increase slightly Sunday as a ridge builds briefly over the region, followed by little change Monday as a large eastern Pacific trough approaches the West Coast.

Here is the latest forecast for Pasadena from the National Weather Service as of 3:38 a.m. on Tuesday, May 20:

Today: Sunny, with a high near 85. Light and variable wind becoming southwest 5 to 10 mph in the morning.

Tonight: Mostly clear, with a low around 63. Southwest wind 5 to 10 mph becoming light and variable in the evening.

Wednesday: Sunny, with a high near 93. Light and variable wind becoming southwest 5 to 10 mph in the afternoon.

Wednesday Night: Mostly clear, with a low around 64. Southwest wind 5 to 10 mph becoming light and variable after midnight.

Thursday: Sunny, with a high near 89. Light and variable wind becoming southwest 5 to 10 mph in the afternoon. Winds could gust as high as 15 mph.

Thursday Night: Mostly clear, with a low around 63.

Friday: Sunny, with a high near 84.

Friday Night: Mostly clear, with a low around 56.

Saturday: Sunny, with a high near 78.

Saturday Night: Mostly clear, with a low around 57.

Sunday: Sunny, with a high near 79.

Sunday Night: Mostly clear, with a low around 58.

Memorial Day: Sunny, with a high near 79.