Increased HeatRisk expected through Saturday with moderate HeatRisk for the mountains and Inland Empire with major to extreme HeatRisk in the deserts. There is a chance 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 marine layer low clouds slowly clearing from the coast. The inversion on the 12Z KNKX sounding was about 10 degrees so clearing at the beaches this afternoon may be patchy. Low clouds will remain constant at the coast each night and morning through the forecast period, reaching into portions of the western valleys at times.
Thursday through Saturday highs will be above average near the coast to 5 to locally 10 degrees above average for some 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 and mountains, widespread 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 to locally extreme 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).
The flow aloft will turn southeasterly Thursday and remain southeasterly into early next week. This would allow for some monsoonal moisture into the area and bring a 15 to 20 percent chance of showers and isolated thunderstorms to the mountains each afternoon. Through Friday, there is only a 15 percent chance of rainfall rates exceeding 0.50" per hour in any showers that develop in the mountains. Current forecast follows the NBM which has chances each afternoon, with most widespread coverage Sunday and Monday.
051800z. Coasts/Valleys, Satellite shows low clouds are quickly eroding back towards the coast, with clearing expected for coastal TAF sites by 19z. Patchy stratus may linger at the beaches through the afternoon. Low clouds redevelop and move inland again this evening, likely after 03z Thur, with slightly lower bases around 1000-1500ft MSL. VIS down to 3-5SM for inland valleys and coastal terrain. Clearing on Thursday will occur a little earlier, likely by 16-18z.
.Mountains/Deserts, SCT-BKN clouds AOA 20,000ft MSL with unrestricted VIS through Thursday.
No hazardous marine conditions are expected through Saturday.
Ca, Heat Advisory until 8 PM PDT Saturday 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 Saturday for Apple and Lucerne Valleys-Coachella Valley-San Diego County Deserts- San Gorgonio Pass near Banning.
PZ, None.
