The first of three storms predicted to sweep through the Inland Empire in quick succession will hit the region Thursday, producing showers and thunderstorms, according to the National Weather Service.
The anticipated rain had prompted county officials to issue a voluntary evacuation order late Wednesday for select areas near the recent Holy Fire burn area.
That order was upgraded after daybreak Thursday to a mandatory evacuation order in the following zones: Amorose, Alberhill (Pacific Clay), Glen Eden, Glen Ivy-A, Glen Ivy-B, Grace, Horsethief-A, Laguna-A, Maitri (Quarry), McVicker-A, Rice and Withrow-A.
County officials urged residents to check maps at www.RivCoReady.org/StormReady to determine if they are in an evacuation area.
Forecasters said a low pressure system rotating south from the Gulf of Alaska will make landfall Thursday morning, though significant precipitation isn’t likely until the afternoon.
Temperatures will peak in the low 60s in the Riverside metropolitan area, with rain amounts generally less than an inch, according to the Weather Service.
The “fast-moving” system will exit to the east Thursday evening, with showers lingering into Friday morning, the NWS stated.
Meteorologists said a second Pacific trough will dominate Southern California late Friday night to Saturday night.
“This will be a larger and slower-moving system, and more widespread and heavier precipitation is expected, along with periods of strong gusty southwest to west winds,” according to the NWS. “Snow levels will lower to around 5,500 feet for Saturday afternoon and evening, with snowfall totals exceeding one foot possible above 7,000 feet.”
Highs in the Riverside metropolitan area will hover in the upper 50s, while daytime temperatures in Coachella Valley communities will be in the low 60s, according to forecasters.
Rainfall in western Riverside County Saturday could range from 1 to 3 inches, while the deserts may receive 1 to 1.5 inches. Isolated locally heavy downpours are possible, and flash flood warnings may be issued, according to the Weather Service.
The final storm in the series is anticipated Sunday night into Monday, but “it is not expected to be as strong as the storm on Saturday,” the NWS said.
Multiple neighborhoods fell under mandatory evacuation orders at intervals between Jan. 14 and Jan. 17, when a storm series triggered locally intense downpours, resulting in a number of street closures. Mud and debris flows, however, did not cause any serious damage to residential properties.
A wide area skirting the eastern side of the national forest, bordering Lake Elsinore and the Temescal Valley, was left exposed to potential flood damage because of the 23,000-acre Holy Fire in August. The blaze, allegedly the work of an arsonist, denuded steep terrain below Santiago Peak, permitting water to flow unchecked onto lower slopes where subdivisions are situated.