Another round of widespread rain forecast to hit Southern California will likely jam traffic during the Wednesday morning commute and could cause flooding across Orange County and the Inland Empire, officials say.
Light rain began falling in the Los Angeles area around 8 p.m. Tuesday as an atmospheric river carried tropical moisture in from the southwest. But the bulk of the storm will arrive Wednesday morning and afternoon, with a fast-moving cold front crossing the region from west to east, according to the National Weather Service.
A second, weaker storm could bring more precipitation this weekend, forecasters said.
Motorists should be prepared for delays Wednesday morning, with brief but heavy downpours possible and several areas at risk of flooding.
Last week, an atmospheric river moving across the state dropped record rain- and snowfall during the Thanksgiving holiday. That moisture had been lingering over Central California for much of the past two days.
This week's storm is expected to deliver 0.75-1.5 inches of rain to most the L.A. area, with the potential for up to 3 inches in the eastern San Gabriel Mountains and on other south-facing slopes.
Orange, San Bernardino and Riverside counties are forecast to get 0.75-1.3 inches at lower elevations, but as much as 2-3.5 inches in the San Bernardino County mountains.
Rainfall totals in the High Desert will range from a third to two-thirds of an inch, and around one-third of an inch in the lower deserts, NWS said.
A flash flood watch will be in effect from 6 a.m. to 6 p.m. Wednesday for all of Orange County, the Inland Empire, mountain areas in Riverside and San Bernardino counties and coastal, valley and mountain areas in San Diego County.
NWS expects the danger to be most prevalent in coastal and valley areas between 6 a.m. and noon, with mountains impacted through 6 p.m. as the band of moderate-to-heavy rain moves east.
Morning rainfall rates could briefly reach 0.4 inches an hour in urban areas, making street flooding likely, according to NWS.
Over the mountains, 1-3 inches of rain is forecast through early Wednesday evening. With soils still saturated from last week's storm, mud slides and debris flows are possible on southwest-facing slopes and in recent burn areas, officials said.
There may also be more runoff in the mountains as the wet weather melts recently fallen snow.
Across the Southland, snow will mainly be limited to elevations above 7,000 feet, with 3-6 inches possible.
The precipitation will taper off by Wednesday evening before ending Wednesday night, forecasters say.
Thursday and Friday are expected to be dry and a little warmer before another low-pressure trough moves into the region this weekend, bringing a chance of light precipitation. Less than half an inch is expected to fall Saturday, but rain could become more widespread Sunday.
Drier and warmer weather should return Monday, NWS said.