Strengthening high pressure aloft combined with weak offshore flow on Thursday is expected to bring widespread record heat for Thursday and Friday. Weak onshore flow will bring some cooling for the coast into the valleys for the weekend with little change in the heat for the deserts. Even stronger high pressure aloft is expected to bring widespread record heat for inland areas for next week with some locations exceeding all-time records for March. With widespread moderate or greater heat risk for the valleys, inland coastal areas, and the lower deserts for Thursday and Friday of this week and for much of next week beginning on Monday, heat-related illnesses are likely for sensitive populations.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, New Aviation Discussion for 12z TAF Package,
(today through Friday), High pressure to the southwest will strengthen across southern California through Thursday, then begin to weaken on Friday. Weak offshore lower-level developing late today and peaking on Thursday with strongest north to northeast winds along and below the coastal slopes of the mountains gusting to 25 to 35 mph.
For today, high temperatures will warm from as little as 5 degrees near the coast to as much as 15 to 20 degrees for the inland valleys onto the lower coastal slopes of the mountains. High temperatures today will range from around 70 near the coast to the 80s for the Inland Empire with the lower deserts in the upper 80s to around 90.
For Thursday, additional warming is expected with high temperatures warming as little as a few to around 5 degrees for the mountains and high desert to as much as 10 to 15 degrees for coastal areas into the western valleys. High temperatures for the coast and valleys will be mostly 20 to 25 degrees above average. High temperatures on Thursday for the coast and valleys will range from the lower to mid 80s near the coast to the 90s for the western valleys and inland Orange County with the lower deserts in the 90s.
For Friday, high temperatures for the coast and western valleys will cool slightly while the mountains and deserts warm another few degrees. High temperatures on Friday will range from the lower 80s near the coast to the lower to mid 90s for the western valleys and inland Orange County with the lower deserts in the upper 90s.
Many high temperatures records across much of area are likely to be tied or broken on Thursday and Friday. There will also be some record warm overnight temperatures on Thursday, mainly for the mountains and inland valleys, with many more on Friday.
(Saturday through Tuesday), A weak low pressure system moving inland across the Pacific Northwest on Friday night will weaken high pressure aloft over southern California through Saturday with mid and high clouds spreading across the area for late Friday through late Saturday.
On Saturday, not much change in high temperatures is expected for the deserts while the coast and valleys cool 4 to 8 degrees with high temperatures ranging from the mid to upper 70s near the coast to 80s to around 90 for the valleys and inland Orange County with the lower deserts in the upper 90s.
High pressure aloft will strengthen off the West Coast on Sunday and Monday, then move slowly inland for Tuesday and Wednesday with the strongest high pressure aloft over the southwest states and northwestern Mexico. Warming will begin for the mountains and inland valleys on Sunday with continued warming for most areas on Tuesday and Wednesday.
With the warming, high temperatures on Tuesday will be as much as 25 to 30 degrees above average for the mountains, inland valleys, and high desert with high temperatures ranging from around 80 near the coast to the mid 90s to 102 for the inland valleys with the lower deserts reaching 102 to 106. Some locations in the lower deserts could exceed their all-time record high temperatures for March.
111130z, Very weak offshore flow has prevented much inland low cloud development, with the marine layer hanging around 20 mies out over the water. Bases around 1000-2000ft MSL but are looking less and less likely to impact any TAF sites. Around a 20% chance of a brief CIG at KSAN before 17z, with lower chances for KSNA and KCRQ. Any clouds that make it inland will also be accompanied by low VIS down to 3-6SM. Clearing should occur by 18z, with VFR prevailing thereafter. Low clouds look unlikely again tonight with persistent weak offshore flow.
No hazardous marine conditions are expected through Sunday.
Ca, Heat Advisory from 10 AM Thursday to 8 PM PDT Friday for Orange County Coastal Areas-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire- San Diego County Coastal Areas-San Diego County Valleys.
PZ, None.
