Sunday will be sunny and mild in San Diego County after a cold start, but another Santa Ana wind condition will hit the area Monday and Tuesday with gusty northeast winds and very low humidity in the mountains, valleys and some coastal areas, the National Weather Service said.
Mid- and high-level moisture will increase Sunday night and Monday as an upper trough over Oregon digs south across California before stalling off the coast of northern Baja Monday night, forecasters said.
"This moisture will translate into mid- and high-level clouds, but relative humidity increases will be modest and not too significant,'' the NWS said.
High temperatures in coastal areas Sunday were expected to be 66-71 degrees with overnight lows of 41-48, the weather service said. Valley highs will be 73-78 with overnight lows of 44-51.
Mountain highs were expected to be 62-69 with overnight lows of 36-46. Highs in the deserts will be 73-78 with overnight lows of 45-55.
On Monday night and Tuesday, red-flag conditions will be most widespread when the strongest Santa Ana winds arrive and the relative humidity plummets into the single digits.
Monday will be cooler in the deserts, mountains and inland valleys as the surge of cold air moves in from the north, the NWS said. Tuesday and Wednesday will be warmer, especially west of the mountains with downslope warming raising temperatures into the 80s in some spots.
A weak trough will pass to the north on Thursday and Friday, bringing some weak onshore flow and a few degrees of cooling.