A storm system swollen with moisture from an atmospheric river will bring rain to Southern California from Tuesday afternoon through Wednesday, prompting the National Weather Service to issue a flash flood watch for all burn areas in Los Angeles, Ventura and Santa Barbara counties.
Across Ventura and Los Angeles counties, the heaviest rainfall is expected late Tuesday evening and Wednesday morning, affecting the Thomas, Hill, Woolsey, Stone, South, Creek and La Tuna burn scars, according to the National Weather Service.
Peak rainfall rates during this period are expected to range between a half inch and .80 inches per hour. Additionally, there is the potential for isolated thunderstorms, which could produce higher hourly rates.
The flash flood watch will be in effect from 6 Tuesday evening until 11 a.m. Wednesday.
“Shallow mud and debris flows will be likely, especially in the first-year burn areas, with the potential for more significant and damaging debris flows. In addition, roadway flooding is likely, especially in low-lying areas, along with rock and mudslides on canyon roads and below steep terrain,” according to an NWS statement.
The rain will turn to showers by Wednesday evening, then showery conditions will persist through Friday, said the NWS. Dry weather is expected Saturday, and showers are possible Sunday through Monday.
Rainfall totals across eastern Ventura and L.A. counties should be generally .75 to 1.5 inches in coastal and valley areas, and 1.5 to 3 inches in the foothills and mountains. Through Friday, rainfall for Orange county is expected to range from one half to three quarters of an inch near the coast to 1.5 to 2.5 inches in the mountains, with local amounts to around 3.5 inches.
In the San Gabriel Mountains, a wind advisory denoting an expectation of 35-mile-per-hour winds will be in force from 8 Tuesday evening to noon Wednesday amid south winds of 20-30 mph gusting at as much as 60 mph.
“Gusty winds will make driving difficult, especially for drivers of high-profile vehicles,” warned the NWS. “When driving, use extra caution. Be prepared for sudden gusty cross-winds.”
Snow levels will be high through Wednesday — generally above 7,500 feet, then drop.
In coastal waters, there is the possibility of isolated thunderstorms from this evening through Wednesday morning. The usual thunderstorm risks will be possible, including gusty and erratic winds, rough seas and the possibility of waterspouts.
Another upper low will drop southeastward through the eastern Pacific Sunday through Monday.
The NWS forecast rain in L.A. County Tuesday and highs of 57 on Mount Wilson; 60 in Avalon; 64 at LAX; 65 in Saugus and Long Beach; 66 in Downtown L.A., Lancaster; 67 in Palmdale, Burbank and San Gabriel; 68 in Woodland Hills; and 69 in Pasadena. Rain is forecast for Wednesday, followed by showers Thursday and Friday, sunny skies Saturday, and more showers on Sunday and Monday.
Partly cloudy skies are forecast in Orange County Tuesday, along with highs of 59 on Santiago Peak; 60 in Laguna Beach and San Clemente; ; 65 on Ortega Highway at 2,600 feet; 62 in Newport Beach; 66 in Fremont Canyon; 68 in Yorba Linda; 69 in Trabuco Canyon, Fullerton and Irvine; 70 in Anaheim; and 71 in Mission Viejo. Rain is expected in Orange County Wednesday, followed by showers Thursday, partly cloudy skies Friday, sunny skies Saturday, partly cloudy skies Sunday and more showers Monday.