Thunderstorms And Snow Forecast For California In Dramatic Swing From Heatwave

SOUTHERN CALIFORNIA — A week after record-breaking heat scorched the region, the weather in Southern California is taking a dramatic swing to the other extreme as unseasonably chilly temperatures coincide with rain — and even snow in the Sierra Nevada mountains — the rest of the week.

Temperatures well below average will continue through Thursday across the region, with highs 10 to 20 degrees below normal for this time of year. In the inland Los Angeles Basin — which saw temps exceed 110 degrees during the recent heatwave — highs will hit only the mid 70s as light rain is expected across Southern California, according to the National Weather Service.

The weather shift is happening because one low-pressure system is departing as another makes its way across California. The change largely wiped out the marine layer on Monday. The next low-pressure system should begin making its way down the West Coast early Wednesday, the weather service said.

On Wednesday "the marine inversion should reform and this — along with stronger onshore (flow) — should allow for a little more coastal stratus to form, especially for the Central Coast and LA coast," the NWS said.

North of LA, rain could begin during the day Wednesday as the system makes its way south into LA County. Drizzle or light showers are "possible just about anywhere (in LA County) late Wednesday night into Thursday," the NWS said.

A chance of showers is forecast Thursday on the coast and in the valleys and mountains of San Diego and Orange counties, as well as in the Inland Empire, the San Bernardino County mountains and the Apple and Lucerne valleys.

Less than 0.05 inches of rain is expected in areas south of LA.

The most significant rainfall is expected north of LA, where thunderstorms could also develop given a unseasonably large amount of fuel for such storms. Still, there's a chance the weather system could shift and bring more significant showers farther south than Ventura County, the NWS said.

Farther north, more snow is expected in the Sierra Nevada, where some 3 inches of snow were forecast Monday night. That marked the earliest snow advisory for the area in the past 20 years, the Los Angeles Times reported.

Here's a look at the highs through Thursday:

• high 60s to low 70s in coastal Orange and San Diego counties, slightly warmer inland
• mid 60s to low 70s at the LA County beaches, slightly warmer inland
• mid 70s to around 80 in the San Fernando and San Gabriel valleys
• low to mid 70s in the San Diego County valleys
• low 70s to around 80 in the Inland Empire
• low 80s in the Pass Area
• mid 80s in the Coachella Valley

The drop in temperatures has already led to records being broken in parts of Southern California. Records for the lowest maximum daily temperature were broken on Monday in Big Bear (52 degrees), Idyllwild (58), Indio (91, a tie for 1996) and Borrego (82), according to the NWS.

Things will shift starting on Friday, when a "robust warming trend" takes hold. Six to 12 degrees of warming is on tap for Friday. Highs will rise an additional 5 to 10 degrees on Saturday and a further 1 to 2 degrees on Sunday, the NWS said.

The result is highs 4 to 8 degrees above normal: 70s at the beaches, 80s inland and 90s in the valleys, lower-elevation mountains and far inland areas.