High temperatures for today will still be around 5 to 15 degrees below average for the mountains and Inland Empire. This will be followed by a slow warming trend through the middle of next week with high temperatures for the deserts warming to around average over weekend, but remaining a few to around 5 degrees below average for the coast and valleys for early next week. After today, the marine layer will become a little shallower with night and morning coastal low clouds spreading into portions of the inland valleys late each night.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Tonight through Wednesday,
Currently, there are lower clouds still present over a majority of the Inland Empire, and hugging portions of the coastline with the presence of a weak eddy just west of Oceanside, which will allow for some of these clouds to remain in place and periodically result in skies intermittently going broken to overcast throughout the afternoon.
A longwave trough remains over the northwest CONUS, which continues to influence the region with cooler temperatures and breezy conditions, especially across the higher terrain and within passes/along desert slopes. There is a open shortwave embedded within this trough which transitioning over southern Nevada, and this is helping to tighten the pressure gradient. Stronger wind gusts along the desert slopes and within the Coachella Valley just downwind, and within San Gorgonio Pass will generally be 30 to 40 mph, and locally approach 50 mph at times. These winds will decouple and weaken by later in the evening. Temperatures this afternoon will still be around 5 to 15 degrees below the seasonal average for this time of year. Low clouds will continue to fill back in and lower as heights slightly increase.
Higher pressure will further build in going into Tuesday, which will allow for the pressure gradient to continue to weaken, and therefore afternoon winds will not be quite as strong, but still be a little stronger and gusty for the wind-proned areas. Temperatures will generally be a few degrees warmer as well.
Thursday through Monday,
The pattern will begin to shift to the longwave trough over the western states eventually being replaced by a ridge going into upcoming weekend, which will translate into continued gradual warming. Simultaneously, there will be a lowering of the marine layer as well, with increasing impacts to visibilities during the overnight hours closer to the coastal regions. A little beyond the forecast, as the ridge further builds and expands over the Four Corners region by the middle of next week, it will allow for some monsoonal moisture to be advected in from the southeast and will increase the possibility over afternoon thunderstorms over the mountains and deserts, which is also reflected in ensembles displaying increase PWAT values over the southwest by this time.
301730z. Coast/Valleys/Foothills, Most of the coastal basin remains cloudy (though generally VFR) this late this morning with bases 3000-4500 ft MSL. Clouds eventually scatter out of most areas early this afternoon, though may linger through the day for parts of Orange County and along coastal foothills. Low clouds based 2000- 2500 ft MSL redevelop over San Diego County starting 00-02z Wed. Clouds move northward overnight, filling the coastal basin once again by 10-12z Wed. Low clouds scatter back toward the coastline 16- 20z.
.Mountains/Deserts, West to southwest winds return this afternoon with gusts 25-35 kts along desert slopes and locally into deserts. Gusts to 45 kts through wind-prone passes. MOD up/downdrafts and pockets of LLWS over and east of the mountains. Winds slowly weaken again 06-12z Wed.
No hazardous marine conditions are expected through Sunday morning.
Ca, None. PZ, None.
