California’s first significant summer heat wave is poised to arrive next week.
After a cooler than normal June and a moderately warm Fourth of July, forecast models are now locking onto a familiar summer pattern: a sprawling ridge of high pressure poised to drive widespread heat across the West by midweek.
This style of ridge, sometimes referred to as a heat dome, compresses the atmosphere and trap heat at the surface, setting the stage for broad, multiday heat waves.
The most intense stretch looks to unfold between Tuesday and Friday. So how hot could it get in California, and where could the temperature be most intense?
As always, the ridge’s orientation will play a big role. This one is expected to peak in intensity over New Mexico and Arizona, then gradually shift toward Southern California by late next week. Clockwise winds around the ridge will keep much of coastal California under a southwest flow, just enough to preserve the marine layer and moderate temperatures near the ocean. It’s not a setup for a major heat wave in San Francisco.
The initial surge of heat will arrive Tuesday, hitting the Southwest and interior West first. Places like Phoenix, Las Vegas and Palm Springs will see temperatures pushing 110 degrees, while the heat stretches north through the Great Basin and into parts of Oregon, Washington and Idaho. Cities like Boise, Idaho; Spokane, Wash.; and Medford, Ore., could run 10 to 15 degrees above average, with widespread 90s expected.
Bay Area coastal zones including San Francisco, the Peninsula, the South Bay and the Santa Cruz Mountains look relatively spared, with highs topping out in the 80s to low 90s, especially on Wednesday and Thursday when the heat is expected to peak across much of the state.
But just a few miles inland, the intensity ramps up. Interior parts of the East Bay and North Bay are on track for widespread 90s and likely a few triple-digit days during the midweek surge.
The Central Valley and inland Southern California will bear the brunt starting Wednesday and continuing into Friday. From Redding to Fresno and Bakersfield to Riverside, highs will exceed 100 degrees for several consecutive days, with some spots pushing 105 to 110. The Mojave and high desert zones could run even hotter, particularly Thursday and Friday when the ridge reaches peak influence over Southern California.
Thankfully, this doesn’t look like a prolonged event. Most models show the ridge weakening and sliding eastward by next weekend, opening the door for some temperature moderation, especially along the coast and into Northern California. The heat is likely to hang around a bit longer over the Central Valley and interior Southern California.
That said, any multiday stretch of hot temperatures at this time of the year raises the risk of problematic fire weather conditions. Fine fuels in the Central Valley foothills and western Sierra slopes are already dry. And while this event won’t result in widespread offshore wind, very hot temperatures and low humidity levels could turn conditions to a critical level in inland zones.
Thursday breakdown
San Francisco: Clouds will be tough to shake across much of the city, keeping temperatures on the cooler side. Some afternoon sunshine will break through east of Twin Peaks, but the west side — especially the Sunset and Richmond districts — will likely stay socked in. Highs will reach the low 60s downtown and hover in the upper 50s closer to the coast. West winds will pick up in the afternoon, gusting between 20 and 30 mph. Clouds will return overnight, along with breezy conditions and lows in the 50s.
North Bay: Morning clouds will stretch from the Marin coast through the 101 corridor, clearing by afternoon. Highs will reach the mid- to upper 70s in Novato, Napa and San Rafael, with 80s likely in Santa Rosa and Vacaville. Southwest winds will gust between 20 and 25 mph, stronger in gaps and at elevation. Skies will stay mostly clear inland overnight, with low clouds returning near the water and breezy conditions continuing. Lows will be in the 50s.
East Bay: Clouds will linger along the bayshore in the morning, with clear skies inland. Sunshine will eventually develop across the entire East Bay. High temperatures will be in the upper 60s to low 70s in Richmond, Berkeley and Oakland. Highs will top out in the low 80s in the Tri-Valley. West winds will be gusty at 20 to 30 mph, especially in the afternoon, with higher gusts through some of the interior passes. Mostly clear skies overnight with continued breezy conditions and lows in the 50s.
Pacific Coast and Peninsula: It will be a cool, cloudy and breezy day along the Pacific coast. Highs won’t break out of the upper 50s in Half Moon Bay and Pacifica and winds will be gusty from the southwest at 15 to 25 mph. Across the Peninsula, morning clouds will giveaway to partial sunshine in the afternoon. Temperatures will be cool, with highs in the mid- to upper 60s in South San Francisco and San Mateo. Winds will be quite gusty through the San Bruno gap at 40 mph. Mostly clear on the east side of the Peninsula overnight with clouds at the coast and lows in the 50s.
South Bay and Santa Cruz: Morning clouds will clear quickly across the Santa Clara Valley and Santa Cruz, leading to a mostly sunny afternoon. Highs will reach the mid- to upper 70s in San Jose, Cupertino and Milpitas, with low 70s along the Santa Cruz coast. West to northwest winds will be breezy at 10 to 20 mph, easing overnight. Lows will be in the 50s.