A warming trend will continue through through Monday, with a shallower marine layer. Night and morning low clouds will be restricted to the coast areas and adjacent valleys through this period. Temperatures will peak on Monday around 10 to 20 degrees above normal for inland areas as the center of a ridge of high pressure moves over the region. A cooling trend with a deepening marine layer will return by the middle of next week as an area of low pressure approaches the West Coast.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This morning, The marine layer is about as deep as it was yesterday morning but the low clouds don't extend quite as far inland. The Inland Empire remains clear with little evidence of a coastal eddy to push low clouds into it from the south. High- resolution models still show some low clouds getting into the IE by sunrise, although not as much as yesterday morning.
The ridge of high pressure is well established over the west coast and temperatures today will likely be a little higher than yesterday, especially inland away from the marine layer influence. The upper level high will be at its strongest on Monday which will likely be the warmest day. The marine layer will be at its shallowest with low clouds and fog restricted to the coastal areas and maybe a few miles inland. This will result in high temperatures 10 to 20 degrees above average for the inland valleys, mountains and deserts. High temperatures in the low deserts could reach 110 degrees with overnight low temperatures in the mid 70s. This will result in high HeatRisk for the low deserts on Sunday and Monday. High temperatures could reach 100 degrees in portions of the IE with overnight lows in the low 60s resulting in low to moderate HeatRisk for those areas.
Numerical models are in good agreement through Tuesday with respect to the general large-scale pattern but diverge significantly for Wed into next weekend. The spread in model solutions makes the forecast details uncertain for this period. The models do show the upper ridge beginning to weaken and shift eastward on Tuesday as a low pressure system approaches from the northwest. In spite of the uncertainty, we can say with reasonable confidence that a cooling trend will begin on Tuesday - most noticeable west of the mountains as onshore flow strengthens and the marine layer deepens. Although temperatures will trend lower, they will remain near or several degrees above average, and even with the low pressure trough moving inland over CA late next week, conditions will remain dry for SoCal.
090900z, Coast/Valleys, Low clouds 800-1200 ft MSL are covering the lowlands of Orange County and up to the foothills of SD County, beginning to reach into the Inland Empire. Vis reduced 0-5SM through eastern elevated inland valleys and increasingly through the Inland Empire (from BR/HZ). By 14z, IFR cig chances around 60% for KONT and 50% for KSBD. Scatter out this morning 16-19Z. Slightly lower clouds 600-1100 ft MSL will develop offshore Sat afternoon and move back into coastal areas after 02Z Sun, developing inland 04-08z Sun. With cigs, VIS 4-6SM at times for elevated coastal sites and inland valleys through the I-15 corridor (e.g. KCRQ, KSEE, ). VIS down to 0-3SM and patchy fog through eastern valleys and in parts of the Inland Empire near gaps in elevated coastal terrain.
Mountains/Deserts, Clear and VFR conditions through early Sunday. Breezy westerly winds with gusts 25-40 kts through mountain gaps and desert slopes 22-06Z. Northwest gusts generally 20-30 kts Sat evening over eastern parts of the Coachella Valley.
No hazardous marine conditions are expected through Wednesday.
Ca, Extreme Heat Warning from 10 AM Sunday to 8 PM PDT Monday for Coachella Valley-San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
