Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

259 am PST Fri Jan 24 2020


High pressure aloft near the West Coast will continue warm and dry weather through Saturday with a coastal eddy bringing an increase in coastal low clouds and fog into Sunday. A trough of low pressure moving inland along the West Coast will bring cooling on Sunday with gusty winds in the mountains and deserts. Subtropical high pressure will expand into California early next week with high temperatures warming to near average. High pressure will strengthen late in the week bringing greater warming on Thursday and Friday.


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

Short Term

(today through Sunday), A weak trough of low pressure moving inland along the West Coast early today won't have much impact across southwest California other than to bring some high clouds. High pressure aloft near the West Coast will follow for Saturday with another weak trough of low pressure moving inland along the West Coast late Saturday night and Sunday. Weak offshore drainage flow should keep fog near the coast mostly just off the coast early this morning, but with patchy dense fog where it does reach the coast.

A weak coastal eddy is developing which will persist through tonight and Saturday, and bring deepening of the marine layer and a greater increase in coverage of coastal low clouds and fog for Saturday night and Sunday. Low clouds may persist near the coast much of the day on Sunday.

High temperatures for today and Saturday are not expected to change much being near average at the coast, a few degrees above average for inland coastal and western valley areas, and 5 to locally 10 degrees above average farther inland with the largest departures from average in the inland valleys and some mountain areas.

The trough of low pressure on Sunday will bring stronger onshore flow which will spread cooling inland with high temperatures for coastal areas near to a few degrees below average and near to a few degrees above average in the deserts. There will also be stronger and gusty winds in the mountains and deserts.

Long Term

(Monday through Thursday), Subtropical high pressure over the Eastern Pacific will extend into California for Monday through Wednesday, then strengthen for Thursday and Friday. This will bring warming for Monday through Wednesday with high temperatures around average. Greater warming for Thursday and Friday will push Friday high temperatures to 5 to locally 10 degrees above average.


241000z, Coast, Patchy low clouds will be possible through sunrise, mostly in San Diego County, and up to 5 mi inland. Bases will generally range between 200 and 700 FT, with VIS restrictions to 2-4 SM. Brief periods of VIS 1/4-1/2 SM in FG are not out of the question for KSAN. CIG forecast is of low confidence for KSAN, though prolonged periods of CIGS appear unlikely at this time. The low clouds should gradually decrease in coverage over the next few hours, with high confidence in any rogue CIGS clearing by 16Z. VFR conditions will prevail during the day Friday. Low clouds will return tonight after around 02Z, with slightly higher confidence in CIGS affecting the terminals, particularly in San Diego County. Once again, CIGS could be quite low, between 300 and 800 FT MSL, with VIS restrictions possible for the TAF sites.

Valleys/Mountains/Deserts, VFR conditions will prevail into Saturday, albeit with periods of SCT-BKN high clouds AOA 20,000 FT MSL.


A long-period WNW swell will generate locally high seas on Saturday over extreme southern portions of the outer waters, south of San Clemente Island. Here, seas will peak between 7 and 10 feet, with peaks of 5 to 7 feet over the remainder of the coastal waters.

Tranquil conditions Sunday and Monday. Slight increase in NW winds late Tuesday, though at this time peak gusts appear to stay at or below 20 kts.


Medium (13 second) period WNW swell today will be replaced by a longer (16-18 second) swell from the same direction (~285 degrees) on Saturday. This will result in a transition from elevated surf Friday to high surf conditions on Saturday, most widespread in San Diego County. Surf of 5-7 ft is likely in Orange County, with 5-8 ft in San Diego County. A High Surf Advisory is in effect for all area beaches tonight through Sunday afternoon, when high surf conditions should recede.

Watches, Warnings, Advisories

Ca, High Surf Advisory from 10 PM this evening to 6 PM PST Sunday for Orange County Coastal Areas-San Diego County Coastal Areas.


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