Heavy Rain En Route To Lake Elsinore: NWS

RIVERSIDE COUNTY, CA — As an atmospheric river approaches Southern California, National Weather Service officials say Riverside County residents can expect a heavy dose of rain this week. Though some light rains could begin to reach the region Tuesday night, it's Wednesday night and Thursday that will have you really reaching for that umbrella.

Forecasters say a flash flood watch is in effect for the Inland Empire from late Wednesday through late Thursday as up to an inch of rain may fall per hour "during periods of the most intense rainfall." The NWS expects areas near the coast to be hit with 1.5 to 2 inches of rain between now and Friday morning, while those along the coastal slopes of the San Bernardino County mountains may see between 4 to 6 inches of rain.

"The message today is rain arrives Wednesday night and Thursday for far southwest California including Riverside and San Diego County, some rain in the mountains of Orange and San Bernardino Counties on Wednesday #CAstorm #CAwx but rain starts today north of LA," the NWS said on Twitter on Tuesday morning.

The low-pressure storm system over the Pacific is expected to reach Riverside County sometime Tuesday evening, augmented by a subtropical plume of moisture, with a roughly 20 percent chance of rain overnight and a 50 percent chance early Wednesday morning, the NWS said. Any rain showers that do emerge Tuesday will be moving from west to east, with the Coachella Valley not expected to get any rain until Wednesday night, if at all.

"The main rain event is anticipated Wednesday night into Thursday, with flash flooding and debris flows near recent burn scars possible," the NWS said.

Here's the detailed National Weather Service forecast of Lake Elsinore for the coming days:

Tuesday
Mostly cloudy, with a high near 71. Calm wind becoming southwest around 5 mph in the afternoon.

Tuesday Night
A slight chance of rain after 11pm. Cloudy, with a low around 54. West wind 5 to 10 mph becoming light and variable in the evening. Chance of precipitation is 20%.

Wednesday
A slight chance of rain. Cloudy, with a high near 72. Light and variable wind becoming southwest 5 to 10 mph in the afternoon. Chance of precipitation is 20%.

Wednesday Night
A chance of rain. Cloudy, with a low around 57. Southwest wind around 5 mph becoming calm in the evening. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch possible.

Thursday
Rain. The rain could be heavy at times. High near 64. South wind 5 to 10 mph becoming west in the afternoon. Chance of precipitation is 100%. New precipitation amounts between three quarters and one inch possible.

Thursday Night
Rain likely before 11pm, then showers likely after 11pm. Mostly cloudy, with a low around 50. Chance of precipitation is 60%.

Friday
A slight chance of showers before 11am. Mostly sunny, with a high near 63. Chance of precipitation is 20%.

Friday Night
Mostly clear, with a low around 45.

The Coachella Valley is expected to see much less rain, with a 20 percent chance of precipitation Wednesday night and Thursday morning, and a slight chance of rain Thursday evening. The biggest result of the storm in the Coachella Valley will be mostly cloudy skies, though temperatures should continue to warm. High temperatures in the Coachella Valley were forecast to be 79 Tuesday, 84 on Wednesday and 76 to 81 on Thursday.

— Images via National Weather Service, San Diego / City News Service contributed to this report