Valleywide : Autumnal Equinox Brings Heat Relief

Local weather has cooled off considerably, in part due to an offshore system pushing ocean air into the San Fernando Valley.

But there is a more obvious reason for the reprieve from the heat: the autumnal equinox. That’s when the sun crosses the Equator to make day and night of equal length and marks the beginning of fall, which starts at 5:13 a.m. Saturday, according to the National Weather Service.

“We’re into the waning portion of this year,” spokesman Bill Hoffer said. “And the sun’s rays aren’t as direct as they were in June and July.”

High temperatures across the Valley were in the 80s and 90s on Sunday, and were expected to continue in that range today. By Thursday, however, warmer temperatures may return, Hoffer said.

The cool temperatures have been caused by a high-pressure system off the coast and a low-pressure system inland working together to draw moist ocean air into the Valley, causing low clouds and fog in the morning.

But as that high-pressure system moves inland, it could bring hotter weather to the Valley. When a high-pressure system hovers over the Valley, it blocks out the cooling effect from the ocean and allows hotter desert air to move in.