Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

922 am PST Fri Jan 18 2019

Synopsis

A few remaining showers this morning will dissipate as drier air moves into the region. Dry and much warmer this weekend under a ridge of high pressure with weak offshore flow. Cooler on Monday with some low clouds west of the mountains as onshore flow returns. Dry and warmer again for Tuesday through Friday with offshore flow producing gusty northeast to east winds in the mountains and the coastal foothills. The offshore winds will be strongest on Tuesday.

Discussion

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

A few light showers linger this morning west of the mtns, mainly in San Diego County. Any additional accumulations will be less than one tenth of an inch. The showers will dissipate later this morning as a high pressure ridge builds in from the west and the airmass becomes drier and more stable.

Saturday and Sunday will be sunny, dry and much warmer under a ridge of high pressure with weak offshore flow as a sfc high moves into the Great Basin. Saturday will be the warmer of the 2 days with daytime temperatures in the 70s to low 80s west of the mtns. The offshore flow could produce local wind gusts to 45 mph in the mtn passes and coastal foothills.

A little cooler on Monday with increasing clouds as the flow turns onshore in response to a low pressure trough moving inland to the north. Medium-range deterministic models are also indicating small chances for light precipitation, but the probabilities of occurrence are low at this time.

For Tue through Fri, The low pressure trough moves east into the Great Basin and deepens over the southern Rockies as a ridge of high pressure builds over the East Pac/West coast. This will bring a warming trend with dry offshore flow. The offshore flow will likely bring strong and gusty northeast to east winds in the mtns and areas west of the mtns. Current indications are that the winds will be strongest and most widespread on Tuesday with wind gusts of 50-60 mph possible in wind-prone areas. Daytime temps will be in the upper 60s to low 70s west of the mtns on Tue but by Thu/Fri, temps could be in the upper 70s to low 80s. This warm and dry pattern could extend into next weekend.

Aviation

181620z, Coast/Valleys, Isolated -SHRA will end by late morning. Multiple low cloud bases, ranging from 1500-4000 ft MSL will continue this morning, with clouds scattering by the early afternoon. VIS of 3-5 SM this morning for portions of the valleys will become P6SM by late morning. Low confidence in low clouds affecting aerodromes tonight.

Mountains, Low clouds obscuring ridge tops will clear out by late morning. Breezy east to northeast winds will develop along coastal slopes, through passes and into adjacent foothills tonight. LLWS is possible through the period.

Deserts, Areas of BR, with VIS of 1-3 SM near KTRM, will improve by late morning. Otherwise, unrestricted vis with cloud bases AOA 20K FT MSL.

Marine

A large west-northwest swell from 280 degrees will peak this morning, then gradually subside this afternoon and overnight. The outer coastal waters (30-60 NM from the coast) will have combined seas 12-15 feet at the peak, with 8-10 feet in the inner coastal waters (less than 30 NM from the coast). Periods will be 16-18 seconds. Due to large breaking waves, entrances to harbors and bays will be difficult for small craft. A Small Craft Advisory is effect until 4 AM Saturday.

Beaches

Surf will be highest at the southern San Diego County beaches. During the peak period, surf could locally reach 10-12 feet on west facing beaches south of Encinitas, especially around Sunset Cliffs. Elsewhere for the San Diego County beaches values of generally 6 to 9 feet are expected at the peak, with 5 to 8 feet for the Orange County beaches. A High Surf Advisory is in effect until 4 AM Saturday.

Watches, Warnings, Advisories

Ca, High Surf Advisory until 4 AM PST Saturday for Orange County Coastal Areas-San Diego County Coastal Areas.

PZ, Small Craft Advisory for hazardous seas until 4 AM PST Saturday for Coastal Waters from San Mateo Point to the Mexican Border and out to 30 nm-Waters from San Mateo point to the Mexican Border Extending 30 to 60 nm out including San Clemente Island.

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