Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

541 am PDT Mon Oct 15 2018

Synopsis

Upper level low pressure over Arizona and surface high pressure over the Great Basin will bring periods of strong gusty northeast winds today, with winds not as strong for tonight and Tuesday. The strongest winds are expected for Orange County and the mountains and valleys of San Bernardino and Riverside Counties with damaging wind gusts possible this morning. Periods of weaker and more localized northeast winds are expected for Wednesday through Friday. Coastal areas will warm and inland areas will cool for today. For Tuesday through Friday, coastal areas will cool while inland areas warm. For next weekend, upper level low pressure centered off the Southern California coast could draw some moisture into portions of Southern California with a chance of showers and thunderstorms for late Saturday into Sunday.

Discussion

For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties, Upper level low pressure moving southward through far southern Nevada and the eastern deserts of Southern California will move into western Arizona today. Northeast winds aloft behind this trough of low pressure and surface high pressure over the Great Basin will bring periods of strong and gusty northeast winds today. The strongest winds are expected from the coastal mountain slopes of the San Bernardino and Riverside Counties westward to the Orange County coast with winds of 30 to 40 mph with gusts to 60 mph. Isolated gusts to 80 mph are expected below passes and canyons and near the coastal slopes of the Santa Ana Mountains. The winds are not expected to be as strong in San Diego County with strongest and most widespread winds of 20 to 30 mph with gusts to 45 mph in the mountains and inland valleys.

Periods of northeast winds will continue tonight and Tuesday but are not expected to be as strong and not quite as widespread. Lowest inland humidity will fall to 5 to 10 percent today and around 10 percent on Tuesday.

Cold advection behind the trough of low pressure will bring cooling for the mountains, deserts, and inland valleys today with downslope warming from the western valleys to the coast with high temperatures near the coast around 10 degrees warmer than on Sunday. Inland areas will warm for Tuesday through Friday as the offshore flow weakens.

For next weekend, the GFS and ECMWF are in better agreement in placing the center of closed upper level low pressure off the Southern California coast. In this position, the low could draw some moisture from the east into portions of Southern California. Current model runs have the greatest precipitation coverage in Southern California across San Bernardino, Riverside, and Imperial Counties for late Saturday through early Sunday with the local extended run of the WRF having some additional diurnal convection for the mountains and inland valleys on Sunday afternoon. Slight chance PoPs for showers and thunderstorms have been introduced for some areas for late Saturday into Sunday for now.

Aviation

150900z. Scattered coastal low clouds will disappear by 14Z. Scattered to broken clouds at about 6000-8000 feet msl will gradually clear by 19-20Z. Northeast winds will continue to strengthen this morning and peak between 15-20Z at 20-40 KT with gusts 40-60 KT, particularly in foothills, adjacent valleys and Orange County. LLWS anywhere west of the mountains until these winds surface. Strongest winds between Cajon Summit and Orange County. STG- SVR Up/downdrafts likely over and S/SW of the mountains. Winds will decrease some this afternoon and evening, but continue rather strong through Tuesday morning.

Marine

Gusty northeast winds mainly near Camp Pendleton this morning, but also intermittently anywhere within the stretch between Camp Pendleton and San Clemente Island. These intermittent gusts to 25 KT or higher would be briefly hazardous to small craft through about midday. Lighter winds south of a line from Oceanside to south San Clemente Island. No hazardous marine weather is expected this afternoon through Friday.

Watches, Warnings, Advisories

Ca, Red Flag Warning until 8 PM PDT Tuesday for Orange County Coastal Areas-Orange County Inland Areas-Riverside County Mountains-Including The San Jacinto Ranger District Of The San Bernardino National Forest-San Bernardino County Mountains-Including The Mountain Top And Front Country Ranger Districts Of The San Bernardino National Forest-San Bernardino and Riverside County Valleys -The Inland Empire- San Diego County Inland Valleys-San Diego County Mountains- Including The Palomar And Descanso Ranger Districts of the Cleveland National Forest-Santa Ana Mountains-Including The Trabuco Ranger District of the Cleveland National Forest.

Wind Advisory until 8 PM PDT this evening for Coachella Valley- San Diego County Deserts-San Gorgonio Pass Near Banning.

High Wind Warning until 3 PM PDT this afternoon for Orange County Inland Areas-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire- Santa Ana Mountains and Foothills.

Wind Advisory from 6 AM this morning to 6 PM PDT this evening for San Diego County Coastal Areas.

PZ, NONE.

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