Major Southern California Heatwave Expected This Week; 5–20% Chance Tropical Storm Remnants Could Reach State in September

Forecasters expect a major heatwave across Southern California this week, with downtown Los Angeles reaching the 90s and possibly 100s, and inland areas hotter still.

Original report
weatherwest.com

Industry impact

Elevated wildfire risk and potential extreme heat could disrupt regional flight operations and airport ground handling across Southern California's business aviation hubs.

A powerful ridge building over northern Mexico and southern Arizona is set to bring a major heatwave to Southern California this week, with the most intense heat in inland valleys and deserts. Downtown Los Angeles is forecast to reach well into the 90s and possibly the 100s on multiple days, while the San Fernando Valley and Inland Empire will be significantly hotter, with only a narrow coastal strip retaining some marine cooling.

Forecasters put roughly a 30% chance on the heat becoming considerably more extreme if offshore flow develops between Wednesday and Friday, potentially pushing inland valley temperatures near or above 110°F and beach readings near 100°F, alongside a higher risk of strong downslope "sundowner" winds and elevated wildfire danger. The ECMWF and its ensemble have flagged this offshore flow possibility, which would raise the potential for record-breaking heat.

Overnight minimum temperatures across California have been exceptionally far above normal over the past 30 days, attributed partly to record-warm sea surface temperatures along the California and Baja coast and partly to persistent mid-atmospheric ridging and severe-to-extreme drought across the Colorado Basin. Looking further ahead, a growing number of ensemble models show a 5 to 20% chance that a weakening tropical storm or depression could turn north toward California in early September, a risk considered above average this year due to unusually warm ocean water and reduced wind shear.