Below average temperatures with marine layer low clouds and fog reaching into portions of the valleys through Sunday. Gusty westerly winds expected in the mountains and deserts this afternoon and evening and again Friday afternoon and evening. Warming trend expected Monday through at least the middle of next week. Areas of major HeatRisk possible for the deserts and moderate HeatRisk for inland Orange County, valleys, and mountains mid next week. The marine layer will become shallower next week, staying confined to coastal locations.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Visible satellite this morning showed marine layer low clouds and fog had completely filled in the coastal basin, even filling in the Cajon Pass. The 12Z KNKX sounding showed a hefty inversion of 11 degrees Celsius, which will make for slow clearing today especially for the coast. The marine layer is expected to be a similar depth tonight into Friday morning. Patchy drizzle may develop along the coast, but confidence is not high enough in widespread drizzle to add to the official forecast. The marine layer will stay fairly deep through the weekend, reaching into the valleys each night and morning.
High temperatures through the weekend will be below average for most locations due to a passing trough. In addition to cooler conditions (and the deeper marine layer), elevated southwest to west winds can be expected. Winds during the afternoon and evening for the mountains and deserts will be strongest on Friday with gusts 30 to 40 mph and with gusts to 55 mph in the northern Coachella Valley below the San Gorgonio Pass.
By Tuesday, an upper level area of high pressure will have built into the desert southwest. This will shrink the marine layer and result result in 3 to 5 degrees of warming between Monday and Tuesday. Through the week, the high will drift west. This will bring above average conditions to inland areas. Current forecast follows the NBM for Tuesday through next Thursday which will bring high temperatures 5 to 10 degrees above average with areas of moderate HeatRisk away from the coast and areas of major HeatRisk in the low desert. Hottest conditions based on current forecast are expected to be Wednesday and Thursday. Ensemble guidance is also indicating an increase in precipitable water for the middle to end of next week. That would result in warmer than normal overnight low temperatures and a disrupted marine layer limiting low cloud development.
The spread in potential forecast solutions starts to increase for the middle to end of next week. Ensembles are indicating the possibility of a shortwave trough moving through California, which would result in a few degrees of cooling if it verifies. Right now the solutions are split fairly equally for Thursday with 51 percent of solutions bringing in the shortwave trough and 49 percent keeping the ridge aloft. If the ridging were maintained, that would prolong the above average conditions into the end of next week. Any increase in high or low temperatures above current forecast will likely result in more widespread moderate or major HeatRisk, especially for the end of next week. We'll continue to monitor forecast trends in the coming days.
181758z, Coast/Valleys, Low clouds 1800-2800 ft MSL with Tops to near 3500 feet clearing back to the coastal areas. There will likely be some localized low clouds lingering along parts of the coast through most of the afternoon, highest chances in southern San Diego County vcnty La Jolla. There is a 60% chance KSAN could only partially/intermittently clear. Clouds with similar bases will become more widespread and move back into coastal regions after 00Z Friday, then back to cover most of the coastal basin again by 12Z Friday.
Mountains/Deserts, VFR conditions. Breezy westerly winds gusting 25-30 kts through mountain passes and into deserts 18Z through 09Z Friday. There could be temporary VIS restrictions due to FU (wildfire smoke) in an around the Coachella Valley area through Thursday evening.
No hazardous marine conditions are expected through Monday.
Elevated surf and strong rip currents continue through Friday. Surf of 3-5 feet with local sets to 6 feet are expected at south-facing beaches. Surf for southern San Diego County will be slightly lower, but hazardous swimming conditions with high rip current and longshore current risk will still exist. See the Beach Hazards Statement for more details.
Ca, Beach Hazards Statement through Friday evening for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, None.
