Dry and warmer conditions this weekend with weak Santa Ana winds. A pattern change is expected next week, bringing cooler conditions, periods of gusty southwest to west winds, and a 15-35% chance of precipitation at times Tuesday through Thursday and again late next Saturday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Areas of low clouds have developed in the inland valleys with scattered high clouds continuing to move north over the region. Low cloud coverage will remain patchy through the morning. An upper level low currently centered around 250 mi southwest of San Diego will move south along the Baja coast today and Sunday and an east-west oriented upper level ridge axis moves overhead. Surface pressure gradients trend offshore into Sunday, producing weak north to northeast winds near the passes and foothills tonight into Sunday morning. This will bring warmer, dry, and mostly sunny weather through the weekend. By Sunday highs will be in the low 80s in many of the valleys once again, and in general 10-15 degrees above normal across the region.
The upper level ridge weakens on Monday with weak onshore flow returning during the day, allowing for a few degrees of cooling. A more significant pattern change is expected the remainder of the week. Global ensembles are in generally good agreement with bringing a short wave trough across CA Tuesday into Wednesday. However, there is still uncertainty with how much moisture will make it into So Cal with this system and the timing of any precipitation. A second short wave is forecast to dig south off the coast with the energy splitting into a wave that moves inland across Central CA on Thursday with the base of the trough digging well south and inland across Baja around Friday, taking most of the moisture with it. What is more certain is that it will be much cooler with high temperatures returning to around normal, and onshore flow will strengthen with gusty southwest to west winds in the mountains and deserts at times.
For the 48 hrs from 4 AM Tue through 4 AM Thu, the NBM has around a 70% chance of measurable precipitation (at least 0.01") for the mountains westward, though the probability for any 6 hour period is only 15-35%. Chances of 0.25" or more during this time frame range from around 20% in southern San Diego County to around 40% for northern Orange County, and around 35-60% along the coastal mountain slopes. For the second wave 4 AM Thu through 4 AM Fri, the NBM has around a 45% chance of measurable precipitation for the mountains westward, and a 15-20% chance of at least 0.25". There is also significant spread in snow levels with the 25th-75th percentiles ranging anywhere from 5000-5000 ft on the low end to 6500-7000 ft on the high end.
Transitory ridging moves overhead on Friday for minor warming and dry weather. Another upper level trough approaches on Saturday for cooler weather and a 30-40% chance of precipitation by the evening.
071000z. Coast/Valleys, Low clouds have filled into the San Diego valley and the Inland Empire with bases around 1,200- 3,500ft MSL. Coverage will be patchy, especially along the coast, with intermittent MVFR/VFR conditions. Low clouds are expected to scatter out of most land areas around 13-16Z, but may linger over coastal Orange County through 18Z. Low clouds will return in the late afternoon/early evening for coastal San Diego County with lower bases around 1000-1500 ft MSL. Light offshore flow will help keep coverage of low clouds patchy and confined to coastal areas Saturday night.
Mountains/Deserts, VFR conditions expected through the period with FEW-SCT high clouds above 20,000ft.
Westerly swell (280 degrees) at 15-16 seconds will bring seas of 6-9 feet in the outer waters near/around San Clemente Island today. This may also lead to localized steep, rough conditions near the bay entrances, including the entrance to the San Diego Bay/Zuniga Shoal area and Oceanside Harbor. Otherwise, no hazardous marine conditions are expected through Thursday.
Increasing long-period (15-16 second) swell from the west-northwest (280 degrees) will bring elevated to high surf of 5-8 feet with locally higher sets to 10 feet through early Sunday morning. Impacts will be greatest at west facing beaches, especially across southern San Diego County with a high risk for rip currents. This may also lead to minor tidal overflow for low-lying beach areas during high overnight into the early morning hours. Further information can be found in the High Surf Advisory.
Ca, High Surf Advisory until 6 AM PST Sunday for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, None.
