Slight cooling through Sunday, though warm, above average temperatures persist, with a return of marine layer low clouds and fog at the coast during the mornings. Slight warming next week as weaker high pressure builds back into the region, with temperatures 10-25 degrees above average through at least Friday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Intense, early season high pressure that brought unseasonal, multiple-record breaking heat has finally weakened and shifted eastward as a low pressure system in the Gulf of Alaska finally flattens the persistent ridge that covered the western half of the U.S. For the last week. Compared to temperatures at noon yesterday, today's noon temperatures are anywhere from a degree to twelve degrees cooler. Sunday's high temperatures will be another 2-6 degrees cooler as a small, transient low moves through the region. Despite this, we're not close to being out of the woods in terms of unusually warm temperatures, with even Sunday's high temperatures remaining 5-20 degrees above average.
As heights aloft drop and pressure gradients turn onshore, our long-absent marine layer will make a return to coastal regions mornings over the weekend into early next week, though a somewhat patchy one at points. Persistent high pressure will keep clouds to within 10-15 miles of the coast or so, and low enough that patchy mist and fog are likely over coastal highlands. Onshore flow will also lead to breezier afternoon and evening winds today through Monday for the mountains and deserts, with areas locally gusting 20-35 mph this evening.
Ridging moves back over the region Monday-Tuesday, then amplifies through mid-week as it moves eastwards into the desert southwest. As a result, temperatures will increase again Monday-Wednesday by a degree or two each day, but not to the extent of this previous week. Temperatures Wednesday will be 10-25 degrees above average for this time of year. Coastal areas will remain in the mid to high 70s, with 80s to low 90s in the valleys, low to mid 90s in the IE and high desert, 70s in the mountains, and mid 90s to about 101 in the low deserts. Several daily temperature records are likely to be tied or broken over the next week for inland sites, but monthly records at least are very unlikely to be challenged.
Little change day to day from mid-week to late week as high pressure remains over the area and temperatures remain well above average. A pattern shift does appear to be in our future, however, with the majority of long range models showing some form of low pressure trough near the end of the month. High uncertainty remains as there are some significant model differences, but at least some cooling is very likely.
211800z, Currently a patch of low clouds around 300 ft MSL are hanging out just off the southern San Diego coast. Higher chances for fog and low clouds for coastal sites this evening beginning after 02Z Sunday. Cloud bases are expected to be around 300-800 ft MSL, increasing in coverage 6Z-9Z. Vis restrictions around 2-5SM with fog along elevated coastal terrain are expected to develop 7Z- 10Z. Low clouds and fog will begin to clear 16-18Z Sunday. Otherwise, VFR conditions expected through the period.
Patchy, but not dense, fog out over the local waters currently. Fog is expected to increase in coverage this evening with locally reduced visibility under 1 nautical mile possible. Visibility will improve by late morning Sunday. Otherwise, no hazardous marine conditions expected through Thursday.
Ca, Extreme Heat Warning until 8 PM PDT this evening for Coachella Valley-San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
