Monsoonal moisture will decrease this weekend, with a slight chance of showers and thunderstorms for the mountains and lower deserts returning for Monday afternoon. Above average high and low temperatures will continue through next week. Widespread moderate to locally major HeatRisk for the coast, valleys, and mountains except near the beaches and for the higher elevations in the mountains, with major to extreme HeatRisk for the lower deserts.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED AVIATION DISCUSSION,
A couple of record high minimum temperatures were set yesterday as moisture aloft and high clouds inhibit radiation cooling at night. A few high clouds continue this morning as patchy marine layer low clouds form over the coastal areas.
Numerical models remain in good agreement with respect to the synoptic pattern. The dominant high pressure will remain in place over the southwest US with some variations in the location of the center and orientation of the ridge axis, with the ridge becoming less amplified at times as a couple of major shortwave troughs move inland over the Pacific Northwest. As a result, the marine layer will remain shallow with low clouds restricted to the coastal areas and little day-to-day change.
Daytime high temperatures will likely remain generally 5 to 10 degrees above normal. Guidance also indicates that overnight low temperatures will remain above normal. These temperature trends make it more likely that the inland valleys, mountains and high desert will experience moderate HeatRisk through next week with some areas of Major HeatRisk. The lower deserts will likely experience persistent Major HeatRisk through next week. The one caveat is that the changes in position and orientation of the high could result in a reduction of deep-layer moisture aloft. This will certainly reduce the chances for pm showers/tstms in the mtns and deserts but could also allow for improved radiation cooling at night leading to lower overnight temperatures. At this time lower overnight temperatures seems to be a low probability of occurrence.
220930z, Coast, Patchy low clouds based 700-1000 ft MSL will become more widespread, mostly in San Diego Co, through about 12Z this morning, with more intermittent clouds in coastal Orange Co. Clouds scatter out 15-16Z. Low clouds expected to be more patchy and isolated when they form Sat evening, with a 20-30% chance for cigs in coastal San Diego Co after 09Z Sun and lower chances elsewhere.
Otherwise, FEW to SCT clouds above 20 kft MSL through the TAF period.
No hazardous marine conditions are expected through Wednesday.
Ca, Heat Advisory from 10 AM this morning to 8 PM PDT Monday for Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains- San Diego County Valleys-Santa Ana Mountains and Foothills.
Extreme Heat Warning until 8 PM PDT Friday for Coachella Valley- San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
