Temperatures soared into the triple digits again Sunday, as the Southland sweltered under a weekend heat wave that prompted a heat advisory from forecasters and warnings from health officials.

Sunday’s high reached 90 degrees in downtown Los Angeles, 99 in Pasadena, 101 in Van Nuys, 104 in Acton and 107 in Lancaster.

In neighboring Orange County, Fullerton reached 96 degrees, according to the National Weather Service.

The NWS attributed the hot weather to a strong upper level high centered over Arizona and New Mexico. A heat advisory was in effect until 8 p.m. Sunday in the San Fernando, San Gabriel and Santa Clarita valleys, both the San Gabriel and Santa Monica mountains, and inland Orange County and the Santa Ana mountains.

A cooling trend is expected to begin Monday, but temperatures in the 90s will last at least through Thursday in some valley areas, forecasters said. They added that dry conditions and increased winds will create critical fire weather conditions into Tuesday.

The weather service urged area residents to stay hydrated by drinking plenty of water, confining strenuous work or exercise to early morning or evening hours, and wearing lightweight clothing.

And, it stressed, “never, ever, leave children, elderly and pets in an enclosed car, even with the windows down during this heat.”

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