Major spring storm to bring heavy rain, mountain snow to Southern California: Timeline

Weather Forecast for Tuesday, April 7

The latest forecast and air quality conditions for the greater Los Angeles area, including beaches, valleys and desert regions.

LOS ANGELES - Southern California is beginning a transition from record-breaking spring heat to a much cooler, unsettled pattern that could bring widespread rain and mountain snow by Friday. according to the National Weather Service.

What we know:

A weak upper-level trough is moving into the region Tuesday, increasing onshore flow and deepening the marine layer.

This shift will drop temperatures by 3 to 6 degrees in most valleys and up to 10 degrees along the coast, according to the latest forecast.

While Wednesday will see a brief return to warmer conditions due to shifting winds, a more significant storm system is tracking toward the coast for the end of the week.

Current forecasts indicate an 80% likelihood of rain across the region, the NWS said.

Rainfall totals are currently estimated at around a half-inch for most areas, though convective "bursts" or thunderstorms could push those totals to an inch or more in specific locations.

In the mountains, snow levels are expected to drop to between 7,000 and 9,000 feet, potentially bringing light accumulations to high-elevation peaks.

Forecasters are also monitoring the potential for isolated flooding if the predicted thunderstorms develop over areas with high soil saturation.

What we don't know:

The exact timing and intensity of the rain is uncertain. 

Timeline:

• Tuesday: Noticeably cooler; highs drop 3–10 degrees with increased coastal clouds.
• Wednesday: A brief warm-up; expected to be the warmest day of the week.
• Thursday: Cooling resumes; cloud cover increases as the storm system approaches.
• Friday Night – Saturday: Peak storm activity; widespread rain, possible thunderstorms, and mountain snow.
• Sunday: Lingering showers possible with cool highs remaining in the 60s.

What's next:

Be prepared for a wet weekend by clearing gutters and securing outdoor items, as gusty winds may accompany the Friday night front. 

Drivers should anticipate slick roads and potential travel delays, particularly on mountain passes where snow or heavy downpours could impact visibility.