The first rains of the fall season are forecast throughout the Inland Empire beginning Wednesday and continuing off and on to Saturday morning, according to the National Weather Service.
“We’re monitoring an incoming low pressure system that is currently developing north off the coast of the Pacific Northwest,” according to an NWS statement. “This low will slowly move south and east over much of this week, eventually bringing cooler and wetter conditions to Southern California.”
The storm system is not anticipated to turn intense until Friday afternoon or evening, with only scattered light rain in the region Wednesday and Thursday, forecasters said.
“Count on at least some measurable rainfall Wednesday night and Thursday,” the NWS stated. “Think sprinkles to one quarter of an inch. The mountains are expected to see accumulations on the upper end of that range.”
Surface prognostication charts published by the agency indicated back-to-back troughs crossing the region over the three-day period, but meteorologists said the bulk of the moisture will stay off the coast and to the south until Friday.
“The highest (probability) for heavier rainfall rates is late Friday for most locations,” the Weather Service said. “So that period holds the greatest potential for any significant runoff or flood threat.”
After the storm system exits to the east Saturday, it will be replaced by a ridge of high pressure, which will influence weather patterns going into next week, with generally warmer, drier conditions for the Thanksgiving holiday period, according to the NWS.
Temperatures in the Riverside metropolitan area Monday and Tuesday will reach 80 degrees during the day and the low 50s overnight, but Wednesday to Saturday will see a slight cooling trend, with daytime highs peaking in the low 70s and lows holding in the 50s.