Showers were expected to consolidate along the coastal slopes early Monday and a strong cold front was predicted to follow from the second of three winter storms this week, the National Weather Service said.
A solid band of showers will accompany the front, with rain rates as high as two- to three-tenths of an inch per hour, forecasters said. They will be moving at a good clip, so excessive rainfall is unlikely.
The snow level is predicted to plummet behind the front from around 4,000-4,500 feet, to 2,500-3,500 feet, the NWS said. Heavy snow will likely accumulate above 3,500 feet in the mountains, while scattered showers continue at times west of the mountains through Monday night.
"A few of these could be briefly heavy with small hail and thunder as the atmosphere will be quite unstable," forecasters said. "Local ponding of water and urban flooding is possible near these heavier showers, and if they repeat over the same area, but the threat of flooding overall is low and any runoff will be limited."
Over the coastal waters, gale force winds and dangerous seas will develop Monday with strong winds along the coast as well.
The bulk of the precipitation is expected to fall through Monday morning.
Travel impacts are predicted to be severe Monday, with several inches of snow affecting all mountain areas and major passes such as Interstate 15, the Cajon Pass, and particularly Interstate 8, where snow may be heaviest. More minor accumulations were expected for lower elevation areas including the far inland valleys and the foothills of San Diego County, the NWS said.
The cold air mass aloft will contribute to an unstable environment and a chance of thunderstorms.
"In addition to the rain and snow, this system will pack a punch when it comes to winds," forecasters said. "This is especially the case for our coastal communities, particularly San Diego County coast, where sustained winds of 25 to 35 mph, and gusts to 50 mph, and locally even higher, can be expected on Monday, strongest in the afternoon."
This will be a significant wind event for the coast, the NWS said, as coastal zones are rarely impacted by winds this strong, so there is a high likelihood of downed trees and tree limbs, and damage to weak fencing.
The midweek period will feature quiet weather with gradual warming ahead of another large and slower-moving storm bringing heavy rain and mountain snow to northern and central portions of the state. That one could arrive in San Diego on Thursday night or Friday with more widespread rain and higher snow levels.
The following warnings and advisories from the weather service will be in effect Monday and Tuesday.
— A winter storm watch will be in effect Monday morning through Monday evening for San Diego County mountains.
— A high surf advisory will be in effect from 6 a.m. Monday to 6 p.m. Tuesday for San Diego County coastal areas.
— A gale warning from 2 a.m. Monday to 10 p.m. Tuesday for coastal waters from San Mateo Point to the Mexican border and out to 30 nautical miles from San Mateo point to the Mexican border.
