Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

1031 am PST Fri Dec 15 2017

Synopsis

The strong high pressure ridge over the eastern Pacific will remain in place through next week. A disturbance will drop south along the eastern side of the ridge on Saturday, briefly drawing moist, marine air back over the region and setting up a cooler weekend. As it passes to the southeast, the dry offshore winds will return on Sunday. Not quite as warm next week, but continued fair and dry with above average temperatures.

Discussion

For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,

At 9 AM PST, water vapor satellite imagery displayed an upper-level ridge off the West Coast nudging into central California, and an upper-level trough off the Pacific Northwest. A 1031 mb surface high over east central Arizona and a 1019 mb surface low near San Clemente was creating easterly wind gusts 30-40 mph mostly along the coastal mountain slopes and foothills in San Diego County. The highest wind gust this morning was 69 mph at Sill Hill. Check out our highest wind gust summary headlined on our webpage. Winds will diminish through the afternoon as offshore pressure gradients weaken. Highs 5-15 degrees above normal will continue today with ridging aloft.

The aforementioned trough will quickly swing across southern California Saturday, which will help lower high temperatures to near seasonal normals, return onshore, westerly flow across most of the area and somewhat increase humidity. Instability and moisture may be sufficient enough to generate a shower or two over the coastal waters. Once the trough moves to our south, northerly flow will set up across the region. This, along with building high pressure over the Great Basin, will create yet another round of gusty Santa Ana winds across portions of San Bernardino, Riverside and Orange Counties Saturday night through Sunday. Due to the direction of the winds, San Diego County should avoid the higher gusts. North to northeast winds of 20-30 mph, with gusts to 50 mph are possible along coastal mountain slopes, canyons and through the Cajon Pass. Isolated gusts could reach near 70 mph in the usual windiest locations. Mountain waves are possible, and could help gusty winds surface over portions of the Inland Empire and coastal Orange County. Winds will diminish overnight Sunday night, but remain weak and offshore through Tuesday. A cold airmass will help low temperatures dip into the 20s for a good portion of the High Desert Sunday and Monday mornings.

The upper-level ridge will remain strong and anchored to our west through next week, which will allow for another trough to swing across the Great Basin. This will help switch our flow back to onshore and westerly on Wednesday, but then could generate another round of Santa Ana winds late Thursday through Friday once it exits the region. Highs will remain above seasonal normals next week, but not be as high as they have been this week. Unfortunately, no sign of precipitation is on our horizon for the next week.

Aviation

151617z, NE winds 15-25 kt with local surface gusts 30-40 kt will create MOD-STG UDDFS/LLWS over and SW or W of the mountains through about 1800 UTC, then weaken through the afternoon. Otherwise, mostly SKC with P6SM vis through 16/0900 UTC. 16/0900- 1800 UTC, patchy stratus with bases 1000-2000 ft msl and tops to 2500 ft msl developing at the coast and possibly spreading into the valleys.

Marine

No hazardous marine weather is expected through Tuesday.

Watches, Warnings, Advisories

Ca, Fire Weather Watch from late Saturday night through Sunday evening for 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-San Gorgonio Pass Near Banning- Santa Ana Mountains-Including The Trabuco Ranger District of the Cleveland National Forest.

PZ, NONE.

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