Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

522 am PST Mon Jan 18 2021


Today will begin to cool with Tuesday much cooler. Locally gusty north winds will develop today. North to northeast winds will be strongest for late tonight into Tuesday. The winds will become more easterly and spread southward into San Diego County late Tuesday and continue into Tuesday night and Wednesday. Precipitation is also possible for late Tuesday into Wednesday night, mostly across the southeastern half of southern California. The greater precipitation amounts are most likely across the mountains and lower deserts for late Tuesday night and Wednesday. There will be warming for Wednesday and Thursday with drying on Thursday. Low pressure systems from the northwest could bring additional precipitation with cooling for late Friday into Saturday and again for late Monday into Tuesday of next week.


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

Short Term

(today through Wednesday), A low pressure system moving southward off the California coast will bring cooling today with gusty north winds developing. The center of a second closed low pressure system over southern Nevada early Tuesday will move to near Point Conception around midday on Tuesday and to a position south of Point Conception and west of central Baja on Tuesday night. The center of this upper low will begin to move across northern Baja Wednesday night and into northwest Mexico and Arizona Thursday.

This low pressure system will bring cooling, stronger and gusty winds, and chances for precipitation. Tuesday will be the coolest day from most areas with high temperatures, except near the coast, 15 to locally 20 degrees cooler than today.

North to northeast winds will strengthen tonight and be strongest for late tonight into Tuesday along and below the coastal slopes of the mountains of San Bernardino and Riverside Counties, and the Santa Ana Mountains. The winds will become more easterly on Tuesday and spread southward into San Diego County on Tuesday with the gusty east winds continuing through Tuesday night into Wednesday. Ensemble members of the ECMWF show moderate to strong winds for the north to northeast flow areas peaking on Tuesday with mostly moderate strength winds for the east flow areas for Tuesday into Wednesday. However, the ECMWF Extreme Forecast Index shows the winds relative to climo exceeding the 90th percentile for the north to northeast flow locations on Tuesday. For the east flow locations, winds are in the 80th to 90th percentile on Tuesday and exceeding the 90th percentile on Wednesday. A High Wind Watch/Warning may need to expanded southward into San Diego County for Tuesday night into Wednesday with the potential for damaging winds in the windier locations.

As for the precipitation possibilities for Tuesday night into Wednesday, a band of more widespread and heavier rainfall is expected to be drawn northward just off the Baja coast and be wrapped toward the northwest and west on the north side of the upper low center. This precipiation is expected to remain to the southwest and south of southern California.

Some precipitation may move westward across northern Arizona and into portions of southern California for Tuesday afternoon and night. Any precipitation for southwest California would most likely be fairly night with the greatest potential for rainfall over the mountains and lower deserts.

For late Tuesday night into Wednesday night, additional moisture and precipitation could be drawn northward ahead of the upper low. Much of this precipitation would move into northwest Mexico and into southern Arizona, put some of this precipitation may extend into the eastern deserts of southern California. There is some potential for this precipitation to extend as far west as the mountains and lower deserts of southwestern California. These areas could receive one quarter to one half inch of rainfall with the potential for one inch or more of rainfall across portions of the lower deserts in southern California.

After the significant cooling on Tuesday, significant warming is expected on Wednesday with not much change in high temperatures for Thursday.

Long Term

(Thursday through Sunday), Thursday is expected to be dry and warmer. Low pressure systems from the northwest could bring more widespread precipitation for late Friday into Saturday and again for late Monday into Tuesday of next week. There will also be cooling with well below average high temperatures for the weekend through early next week.


181030z, Mostly clear with unrestricted vis today and tonight. Fog is possible near KSAN through 16Z with vis 2SM or less. More widespread low clouds with bases 500-800 feet MSL and areas of vis 3- 5SM developing after 03Z spreading into coastal areas early Tuesday. Strong northeast winds 20-30 kts developing in foothills after 06Z tonight and strengthening Tuesday. LLWS possible in areas in lee of mountains such as KSBD and KONT.


Patchy fog with low visibility will occur this morning in the southern portions of coastal waters. Gusty northeast to east winds will be likely across portions of the waters Tuesday into Wednesday with some gusts possibly reaching 25 knots. Otherwise, no additional marine weather hazards are expected through Friday.


Long-period west-northwest swells will produce elevated to high surf and dangerous swimming conditions through Tuesday. Check the High Surf Advisory and Beach Hazards Statement, along with the Surf Zone Forecast for details.

Watches, Warnings, Advisories

Ca, Fire Weather Watch from Tuesday morning through Tuesday evening for Orange County Inland Areas-San Bernardino and Riverside County Valleys -The Inland Empire-Santa Ana Mountains- Including The Trabuco Ranger District of the Cleveland National Forest.

High Wind Watch from this evening through late Tuesday night for Orange County Inland Areas-San Bernardino County Mountains- San Bernardino and Riverside County Valleys-The Inland Empire-Santa Ana Mountains and Foothills.

High Surf Advisory until 5 PM PST Tuesday for San Diego County Coastal Areas.

Beach Hazards Statement through Tuesday afternoon for Orange County Coastal Areas.


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