The flow aloft will become gradually southwesterly with drying of monsoonal moisture the next few days. There remains a slight chance of showers and thunderstorms for the mountains and deserts from late this morning through this afternoon. In addition to drying aloft, there will also be gradual drying of lower level moisture through early next week. High temperatures will cool through Thursday, then slowly warm into the middle of next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This afternoon through Thursday,
The latest high res models are alluding to more of a drying trend vs previous model runs, and given the mid-level flow becoming more southwesterly, there will likely only be some isolated thunderstorms developing later this afternoon along the mountain/desert interface, and then these will move off towards the northeast and skirt across the deserts by later in the afternoon/evening. With much more troughing upstream influencing the region, temperatures will begin a notable cooling trend from this afternoon into tomorrow. Mucape through a consensus of guidance appears to be roughly around 1000 J/kg over the San Diego mountains by later this afternoon, but the majority of the instability (most unstable CAPE) lies just to the east of our CWA. Given the parameters, and flow in the mid level, it is going to be hard for storms to get going. Though, through orographic lifting, along with some shear, there could be a few storms, with the most likely location being over the San Bernardino mountains on the eastern slopes, and over the San Jacinto area. There may also be a storm popping off over southern San Diego County in the Jacumba area. Otherwise, a transition towards cooler and drier conditions are expected going into tomorrow. Winds will also increase more during the day, with gusts approaching 60 mph within Gorgonio Pass and also gusts of greater than 50 mph across the high deserts. The marine layer should fill in better for tonight in comparison to recent nights as onshore becomes more prevalent, and this will carry into tomorrow morning with increasing ceilings, extending further east into the inland areas. As the trough continues to deepen and propagate closer to the region, it will also allow for a "baroclinic leaf" to develop and provide and extensive mid to high level cloud deck tomorrow, which will also hinder daytime heating, with values becoming around 5 to 10 degrees below the seasonal average for this time of year. The drier air aloft will cut off chances of convection for tomorrow.
Friday through the middle of next week,
Persistent onshore flow will prevail into the early part of the upcoming weekend and then the ridge to the east will begin to expand back towards the west with increasing heights, and thus a gradual warmup back to around seasonal temperatures for this time of year, and even a little above average temperatures will return going into the early half of next week as heights creep back above 595 dm. Due to this, there may need to be heat products issued for the deserts again by Monday, as temperatures look to sore north of 110F for much of the lower deserts and within the Coachella Valley. As this occurs, there will be some recycled monsoonal moisture that may make its way back into southern California, and may give our mountains and deserts a slight chance of afternoon thunderstorms towards the middle of next week, otherwise remaining dry elsewhere through then.
121800z. Coast/Valleys, Increasing (FEW-SCT) cu AOA 20,000ft MSL today, becoming SCT-OVC by Thursday. Patchy low clouds develop tonight, likely right around 1800-2000ft MSL after 03z Thur near the coast, spreading to the Inland Empire after 09z with bases slowly rising to above 2000ft MSL. Bases may rise up to 3500ft MSL after sunrise and retreat back towards the coastline by 16-18z. Potential for lingering stratus through Thursday afternoon. Secondary layer closer to 20,000ft MSL will become more pronounced by then, with cloudy conditions through Thursday afternoon.
.Mountains/Deserts, ISO SHRA/TSRA in the mountains today, most likely from KL35 north into the high desert. CB bases near 15,000ft MSL with tops to 30,000ft MSL. Gusty outflow winds possible VCTY TSRA. Otherwise, increasing high clouds AOA 20,000ft MSL this through Thursday morning with VFR.
No hazardous marine conditions are expected through Sunday.
High tides will exceed 7 feet this evening around 930 PM, resulting in minor tidal overflow of low-lying areas along the beach. Surf will be small and is not expected to contribute to the flooding potential. Check the Coastal Flood Advisory for details.
Ca, Coastal Flood Advisory until 11 PM PDT this evening for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, None.
