Through Sunday, moderate HeatRisk is expected in the mountains and Inland Empire with major HeatRisk in the deserts. There are chances of showers and isolated thunderstorms in the mountains each afternoon through Tuesday. Gradually cooler and drier for the latter half of next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
(today through Sunday), Thunderstorms developed late Thursday evening on the leading edge of a Mesoscale Convective Vortex that has been move westward along border between southern California and northern Baja into an atmosphere that the late Thursday afternoon NKX sounding showed had a most unstable CAPE of 1649 J/kg and an LI of -6. The 06Z RRFS shows the center of the MCV turning toward the northwest and tracking along the vicinity of the southern California coast from northwestern San Diego County into southern Los Angeles County this morning. So far, there's no indication that there is sufficient instability in that area for new thunderstorm development to occur this morning.
The thunderstorms that have been moving toward the west across southern San Diego County overnight should cross the coast around 4 AM and continue to weaken. Gages across southern San Diego County have shown rainfall of 0.25 to 0.50 inch. Through 3 AM, there had been 86 cloud-to-ground lightning strikes across San Diego County since late Thursday evening with 499 lightning flashes of all types (cloud-to-ground, in-cloud, cloud-to-cloud, etc.). Chances for afternoon showers and thunderstorms for the mountains and deserts will decrease for today and Saturday, versus the coverage on Thursday afternoon. Chances for afternoon showers and thunderstorms for the mountains and deserts will increase again to 15 to 20 percent on Sunday.
The HeatRisk is expected to peak on Saturday with widespread major HeatRisk for the deserts and moderate HeatRisk for the mountains and Inland Empire with only a slight decrease for Sunday.
(Monday through Thursday), The slight chance for afternoon showers and thunderstorms for the mountains and deserts will continue through Wednesday followed by slow cooling and drying through the following weekend. A greater decrease in HeatRisk is still expected for Monday and Tuesday. It is unlikely the Extreme Heat Warning for the deserts and Heat Advisory for the mountains and Inland Empire will be extended beyond Sunday.
071030z. Coasts, Very patchy low clouds based 1000-1400 ft MSL will struggle to increase in coverage this morning. Greatest chance (30-40%) for cigs at coastal TAF sites will be 12-15z Fri. Any low clouds should clear to the coastline by 16z. VFR conditions expected Friday afternoon and evening. Low clouds return late Friday night with similar bases and patchy coverage.
Valleys/Mountains/Deserts, SCT to locally BKN clouds AOA 10000 feet MSL through Friday afternoon.
Otherwise, a cluster of showers and storms has a history of producing lightning over the far southern San Diego County. As this activity continues to move toward the west, there is a slight chance for lightning to affect other nearby airports (20% at KNRS, 10% at KSAN). Any storm activity should diminish by 6 AM PDT.
No hazardous marine conditions are expected through Tuesday.
Ca, Heat Advisory until 8 PM PDT Sunday for Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains.
Extreme Heat Warning until 8 PM PDT Sunday for Apple and Lucerne Valleys-Coachella Valley-San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
