The first wave of a powerful atmospheric river storm moved into Southern California Wednesday morning with pelting rain and beginning multiple days of sometimes-heavy rain that has forecasters warning of possible flooding across Riverside County and other areas.
“Widespread moderate to heavy rainfall Christmas Eve with the potential for roadway flooding and localized flash flooding from the coast to deserts,” said the National Weather Service. “Rapid rises in small streams and increased flow in main stem rivers expected.”
NWS forecasted that heavy rainfall from a strengthening atmospheric river spreading southward across the area for Wednesday morning with the heavy rain continuing into Wednesday evening. “Showers will continue on Thursday with another round of more widespread showers for Thursday night into Friday,” according to the NWS.
The NWS issued a flood watch that will be in effect through Wednesday evening for Riverside County valleys and mountains, the Coachella Valley and San Gorgonio Pass near Banning.
Forecasters warned that the heaviest rain is anticipated Wednesday morning through Wednesday evening, with rain falling at rates between a half-inch to an inch per hour, with some locally heavier downpours possible.
Rain falling at such high rates could lead to excessive runoff, resulting in “flooding of rivers, creeks, streams and other low-lying and flood-prone locations,” forecasters said. “Flooding may occur in poor drainage and urban areas.”
The pouring rain will likely be accompanied by gusty conditions, with wind gusts of up to 40 mph possible in Riverside County valleys. A wind advisory will be in effect from 3 a.m. to 10 p.m. Wednesday.
Snow levels are expected to remain above 8,000 feet Wednesday morning, “increasing the potential for rock and mudslides along mountain highways, and debris flows in and below burn scars, especially in the San Bernardino County mountains.”
The snow level could fall to about 7,000 feet by Thursday night, then down to 6,000 feet by late Friday.
Conditions should dry out by the weekend.