Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

333 am PDT Thu may 24 2018


A slow moving low pressure system moving inland through California will maintain a deeper marine layer and stronger onshore flow into the weekend. Into Saturday, there be some drizzle for coastal and valley areas during nights and mornings with limited or no afternoon clearing towards the coast. There will be periods of stronger and gusty southwest to west winds for the mountains and deserts from Friday afternoon into Saturday evening. For Sunday through Tuesday, low pressure over the western states will weaken. There will be a warming trend away from the coast with high temperatures for the deserts warming to around 5 degrees above average for Monday and Tuesday. Night and morning coastal low clouds will extend into portions of the valleys with afternoon clearing getting closer to the coast.


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

Short Term

(today through Saturday), A low pressure system off the California coast will move slowly inland for tonight through Saturday. This will maintain onshore flow, strongest for Friday and Saturday with periods of stronger and gusty southwest to west winds in the mountains and deserts from Friday afternoon into Saturday evening.

The marine layer is near 4500 feet deep with aircraft soundings showing a saturated layer from around 1500 feet to around 4500 feet. There has been some drizzle overnight with the greatest coverage in coastal and valley areas of San Diego County into coastal Orange County with widespread reports of 0.01 inch of precipitation. This deeper marine layer will continue into Saturday with soundings from the local workstation WRF having a saturated layer of similar depth for each night through morning with that layer still moist but not saturated in the afternoons. Drizzle is expected each night through morning with patchy drizzle possibly continuing into the early afternoon in some locations. Limited or no clearing is expected for coastal areas.

There will be little change in high temperatures for coastal and valley areas with high temperatures near the coast a few degrees below average and 10 to locally 15 degrees below average for the inland valleys. Slow cooling is expected for the mountains and deserts.

Long Term

(Sunday through Wednesday), Low pressure will weaken over the western states for Sunday through Tuesday. The marine layer will become a little less deep each day, though low clouds will still extend into portions of the inland valleys for Sunday night into Monday morning and Monday night into Tuesday morning. There will be greater and faster clearing towards the coast though afternoon clearing at the coast could continue to be slow or limited.

There will be a warming trend for Sunday through Tuesday with high temperatures for inland areas on Monday and Tuesday around 5 degree above average. A weaker low pressure system moving inland along the West Coast will bring a cooling trend beginning Wednesday.


240945z, Coast/Valleys/Coastal Mountain Slopes, Low clouds with bases 1300 to 2500 ft MSL and tops to 4000 ft MSL continuing west of the mountains this morning. Higher terrain will be obscured through mid-morning. Clouds slowly clearing inland 16-20Z, with only partial clearing in the coastal areas. Clouds will quickly spread back inland after 25/02Z with similar bases and tops.

Mountain Crests/Desert Mountain Slopes/Deserts, SKC and unrestricted visibility through Friday morning. SW-W winds with sfc gusts 25-35 kt may produce localized LLWS with MOD UDDFS over the mountain crests and into the deserts.


West northwest winds with gusts near 20 knots are possible Friday and Saturday afternoon/evening. Winds will weaken Sunday into early next week.


A long-period south swell of 3-4 ft/15-16 sec will continue to produce elevated surf and hazardous swimming conditions through this afternoon mainly in Orange and northern San Diego Counties. Sets to 7 ft are possible. Surf will begin subsiding tonight.

Watches, Warnings, Advisories

Ca, Beach Hazards Statement through this afternoon for Orange County Coastal Areas-San Diego County Coastal Areas.


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