Through Sunday moderate HeatRisk expected in the mountains and Inland Empire with major to extreme HeatRisk in the deserts. There are chances of showers and isolated thunderstorms in the mountains each afternoon through Tuesday. Coastal areas will continue to see low clouds each night and morning through the forecast period.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Visible satellite at 11 AM was showing areas of high clouds across the area with low clouds off the coast. There remain chances of isolated showers and thunderstorms in the mountains this afternoon. Latest REFS guidance indicates a decrease in the 90th percentile maximum hourly rainfall rate this afternoon, down to 0.45 inches per hour. There is only a 10 percent chance of hourly rainfall rates exceeding that. Guidance continues to indicate 15-20 percent chance of isolated showers and thunderstorms over area mountains through Saturday, with guidance indicating hourly rainfall rates will be less than 0.50 inch per hour.
Through Sunday high temperatures are expected to run 5 to 10 degrees above average for inland areas. Low temperatures will also run above average, most noticeable in the mountains and deserts where lows will be 10 to 15 degrees above average. For the Inland Empire, mountains, and portions of inland Orange County and San Diego valleys moderate HeatRisk is expected which means that folks who are sensitive heat, especially those without consistent cooling/hydration will be most impacted. In the deserts, major HeatRisk indicates anyone may see negative impacts from the heat if precautions aren't taken. Make sure to stay hydrated and if possible avoid strenuous activity during the hottest parts of the day (10 AM to 4 PM). High temperatures are expected to gradually decrease next week, bringing temperatures back down to near or slightly below average by the middle of next week.
For Sunday and Monday, precipitable water values are expected to peak which will result in more widespread shower and thunderstorm chances across the mountains. Shower chances will become more isolated again Tuesday and Wednesday.
061800z. Coasts/Valleys, Satellite shows low clouds have cleared the coast with FEW-SCT high clouds AOA 20,000ft MSL moving in from the south. VFR through the remainder of the afternoon. Patchy low clouds based 800-1200ft MSL tonight develop and move inland likely after 03z Fri, spreading north into Orange County after 07z. 50% chance of a brief CIG at KCRQ. VIS potentially down to 3-5SM for valleys and coastal terrain. Clearing out on Friday should occur at a similar pace to this morning, around 16-18z.
.Mountains/Deserts, ISO SHRA/TSRA (15% chance) may develop along mtn ridges 20-23z. Otherwise, FEW-SCT cu AOA 20,000ft MSL with unrestricted VIS into Friday.
No hazardous marine conditions are expected through Monday.
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.
