A car on the northbound Harbor Freeway (I-110)
© John Antczak
A car on the northbound Harbor Freeway (I-110) in downtown Los Angeles plows through deep water during a torrential downpour on Monday, April 6, 2020. Snow and rain fell Monday on California as spring delivered the kind of stormy weather that was missing most of the winter. Numerous spinouts were reported on Los Angeles-area freeways, and there were scattered reports of roadway flooding and canyon road rockfalls.
A powerful storm moved into the Los Angeles region Sunday night, setting a new rainfall record in just hours. On Monday, the heavy-rainfall had officials onguard for the chance of flooding, mudslides over slopes denuded by wildfires as well and dangerous driving conditions in the mountains.

The "powerful late-season winter- like storm" was expected to drop as much as five inches of rain in the San Gabriel Mountains, snow along the Grapevine and up to two inches of rain along the coast. After the driest February on record, and a March characterized by small storms, this April storm is one of the biggest to hit the region in months. A record rainfall rate for an April 5 was recorded Sunday at Sandberg in the L.A. County portion of the San Gabriels. The 0.51 inch recorded bested the 0.5 set in 1969.

Hourly rain rates are expected to be between a quarter-inch and a half-inch per hour but could rise to three quarters of an inch on south-facing mountain slopes, where thunderstorms are also possible, forecasters said.

The NWS warned that this week's conditions may result in a wet commute in L.A. and Ventura counties, travel delays, rocks and boulders tumbling onto roadways, minor mud and debris flows in burn areas, and urban roadway flooding.

Accompanying the rain will be south winds gusting to between 45 and 55 miles per hour.

In the San Gabriel Mountains in L.A. and Ventura counties, a winter storm warning will be in effect until 5 p.m. Tuesday.

The snow level will drop to around 5,500 feet Monday and down to between 4,000 and 4,500 feet by Tuesday morning, and " significant snowfall accumulation is likely in the mountains of Ventura and Los Angeles counties," according to an NWS statement.

Between 15 and 30 inches of snow is expected above 6,000 feet and between 6 and 12 inches between 4,500 and 6,000 feet, according to the NWS. Lighter accumulations are expected down to 4,000 feet by late Monday evening or early Tuesday morning.

"In addition, light snow accumulations are likely on Interstate 5 over the Grapevine by late Monday night or early Tuesday, possibly resulting in travel delays," warned the NWS.

"Heavy snow, gusty winds, low visibilities in blowing snow and icy roads will make for dangerous driving conditions," warned the NWS statement. "These conditions could lead to road closures and travel delays. In addition, light snow accumulations are likely on Interstate 5 over the Grapevine by late Monday night or early Tuesday, possibly resulting in travel delays."

The NWS urged people who have to drive in the mountains to keep an extra flashlight, food, and water in their vehicles.

Thunderstorms are possible across Southern California's coastal waters because of the "cold, potent storm" said the NWS, adding that the storm system will move slowly southward from northern California through the middle of the week.

"Any thunderstorms that form will be capable of producing chaotic locally gusty winds and rough seas, dangerous lightning, heavy rainfall with reduced visibility, and isolated waterspouts, The NWS warned in a statement. "If a waterspout is spotted, head away at a 90 degree angle from the apparent direction."

The NWS forecast rain in L-A. County Monday and highs of 41 on Mount Wilson; 55 in Palmdale and Lancaster; 57 in Saugus; 60 in Woodland Hills, Burbank and San Gabriel; 61 in Avalon and Pasadena; 63 in Long Beach; and 64 in Downtown L.A. and at LAX. Showers are forecast Tuesday, Wednesday and Thursday, followed by cloudy days.

The NWS forecast showers in Orange County and highs of 41 on Santiago Peak; 49 on Ortega Highway at 2,600 feet; 54 at Fremont Canyon and Trabuco Canyon; 57 in Yorba Linda; 58 in Laguna Beach; 59 in San Clemente; 60 in Anaheim and Irvine and 61 in Fullerton. Showers were forecast for Tuesday, Wednesday and Thursday, followed by cloudy days.

City News Service and Patch Staffer Paige Austin contributed to this report.