A brief but substantial storm is expected to bring heavy rain, thunderstorms and possible flooding to Southern California beginning as early as Monday evening, prompting evacuation warnings for residents near recent burn areas.

The rain could begin as early as late Monday night and is expected to produce between three-quarters of an inch to 1.5 inches of precipitation across most areas, with 2 to 4 inches possible on south-facing mountain slopes, according to the National Weather Service. Forecasters said as much as 5 inches could potentially fall in the San Gabriel Mountains.

"All areas will see rain. Some areas will see short bursts of heavy rain, although it remains difficult to predict exactly where," according to the NWS. "South-facing slopes and foothills have the highest chance of seeing those heavy bursts, but they can happen anywhere."

Hail and gusty winds are threats, with waterspouts or a weak tornado possible, the agency added.

"The peak of the storm remains focused on (Monday night) through Tuesday afternoon," according to the NWS. "... Rain rate forecasts will likely be increased, especially for any south- and southwest-facing slopes. Nearly every high-resolution model is showing streaks of heavy rain moving through the region, and while not every area will see them, these narrow bands could happen anywhere. Several of the projections are now showing the rain the organizing and intensifying as it swings into LA County, which is concerning for the recent burn scars -- especially the Eaton and Bridge scars."

In advance of the rain, evacuation warnings were posted for most recent burn scar areas, including the Palisades and Eaton fires, along with the Hurst Fire in Sylmar and the Sunset Fire in the Hollywood Hills. Residents were urged to prepare to evacuate due to the possibility of flooding and debris flows.

"While this may be a short-duration storm, even a burst of intense rain can quickly create dangerous conditions in burn areas," Los Angeles County Public Works Director Mark Pestrella said in a statement. "Our crews are ready, and we urge residents to make personal safety their top priority. Avoid driving on mountain roads or in burn areas, if at all possible, and keep trash cans and vehicles off streets to allow storm runoff to travel freely."

Los Angeles Mayor Karen Bass said city crews were gearing up for the storm and possibility of mud and debris flows.

"The city has bolstered the hillsides and vulnerable areas from potential debris flows in recent burn scar areas -- these resources remain in place," Bass said in a statement. "Today, we have strategically deployed resources for the Palisades and across the city, including strike teams, rescue teams and helicopters. Be cautious on the roads, pick up free sandbags if needed and sign up for emergency alerts at NotifyLA.org. To all Angelenos: stay safe, stay informed and follow official evacuation guidance."

The NWS advised residents to take precautions, remain indoors as much as possible and avoid parking vehicles near tall trees that could be uprooted.

"Avoid the roads as much as possible, and if you have to drive, allow extra time as traffic will be increased due to slippery roads, low visibility, and localized flooding," forecasters said. "If you are near a burn scar, there is a risk of significant debris flows. Heed the advice of local officials, and expect at the very least mud and debris on some roads."

A flood watch will be in effect Monday night through Tuesday evening in recent burn areas in Los Angeles, Ventura, Santa Barbara and San Luis Obispo counties, with forecasters saying the storm has the potential to trigger "hazardous and damaging flooding and debris flows."

As of Monday morning, peak rainfall rates of one-quarter to one-half inch of rain per hour were being anticipated, with a slight chance of some areas seeing rates of 1 inch per hour if thunderstorms or heavy showers develop.

The storm system is also expected to bring gusty south to southwest winds Monday night and Tuesday across the Los Angeles County mountains and the Antelope Valley foothills.

Temperatures will drop dramatically Tuesday, with highs staying in the low 60s in most parts of Los Angeles and Orange County. By Wednesday night, the rain will have moved on. Cooler temperatures were expected to continue into Thursday, followed by a "warming trend" for the end of the week.

Several Southland Areas Issue Evacuation Warnings Ahead of Possible Storms, Flooding - MyNewsLA.com