Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

923 pm PDT Tue Jun 15 2021


Hot, dry days will be followed by warm nights this week as strong high pressure aloft dominates our weather. A coastal eddy and a deepening marine layer will keep the most intense heat from reaching the coastal areas. Cooler weather returns next week when the ridge breaks down and a trough deepens along the West Coast.


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


It was a hot day today, probably the biggest understatement for those in the desert! Palm Springs hit 120F degrees, breaking the record high for the date, previously 116 in 1961. More record highs were broken. Here is the listing:


ANAHEIM 96 95 IN 2018 1989 CHULA VISTA 89 76 IN 1993 1918 SAN JACINTO 107 103 IN 2007 1948 BIG BEAR 89 87 IN 2000 1960 IDYLLWILD 99 98 IN 1961 1943 CAMPO 106 104 IN 1961 1948 PALM SPRINGS 120 116 IN 1961 1893 BORREGO 117 115 IN 1989 1965

A coastal eddy is spinning up with some low cloudiness already having developed along the southern San Diego coast. Some low clouds will spread north along the coast. It'll be a warm night, even near the coast with slightly higher dewpoints into the lower 60s making it feel slightly muggy after several months of much lower dewpoints. The deserts will continue hot tonight and some parts of the lower deserts may struggle to fall below 90 overnight!

No changes were made to the forecast this evening. See previous discussion below for more forecast details.

Previous Discussion (Issued at 125 PM PDT Tue Jun 15 2021):

Temperatures at 1 PM were approaching record levels at Palm Springs where it was 115 (record is 116). Farther south in the Coachella Valley the temperature at Thermal was "only" 107 due to a low level moisture surge from the Salton Sea that raised the dewpoint to 50F. The dewpoint at Palm Springs was 36F.

Elsewhere, the record high of 87 at Big Bear Lake was tied at 1 PM, and may very well be broken before the day is through.

There weren't any low clouds at the beaches this morning, and the nearest low cloud/fog deck at 1 PM was south of Ensenada. There should be some increase in low clouds near the coast tonight as a Catalina Eddy spins up. This eddy will persist through Wednesday night, and the deeper marine layer will keep the coastal areas in cooler marine air. There may be a few areas of dense fog too. As a result of this deepening marine layer, today may be the hottest day of the week in the coastal zones.

Unrelenting heat will continue in the valley, mountain and desert areas all week, dominated by the strong Four Corners high. Max temps will exceed 100 in the Inland Empire, be from 90-100 in the mountains, from 105-115 in the high deserts, and from 114-122 in the lower deserts. Both highest max and and highest min temperature records will be broken this week.

High resolution models are advertising a stronger and deeper low level moisture surge into the Anza Borrego Desert and the Coachella Valley tonight into Wednesday on breezy southeast winds. This should prevent the temperatures from reaching 120, but the added moisture with make it feel more humid, so there really won't be any relief. The added moisture will keep overnight night lows in the 80s and perhaps the low 90s.

The heat starts to abate in the valleys and mountains on Sunday, and then in the deserts on Monday as the ridge slowly relents as a trough digs down the West Coast. Gradual cooling will continue in all areas Tuesday and Wednesday as the trough slowly deepens and moves south.


160415z, Coast, 700-1000 ft CIGS will spread from south to north along the coast Tuesday night, with coverage increasing after 08-10Z. CIGS possible at KSNA, particularly after 10Z, but confidence is lower. South winds with gusts 10-15 kts will persist most the night as a coastal eddy prevails. Vis 3-6 SM possible for coastal terminals, with local vis to 1 SM for elevated coastal terrain. Clearing likely by 15-16Z. Low clouds will redevelop along the San Diego County coast near 03Z Thu, and a few hours later for Orange County, with similar bases.

Otherwise, SCT locally BKN clouds at or above 20000 feet MSL and unrestricted vis through Wednesday evening.


No hazardous marine conditions are expected through Sunday.

Watches, Warnings, Advisories

Ca, Excessive Heat Warning until 9 PM PDT Sunday for Coachella Valley-San Diego County Deserts.

Excessive Heat Warning until 9 PM PDT Saturday for Apple and Lucerne Valleys-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains-San Gorgonio Pass Near Banning.

Excessive Heat Warning until 9 PM PDT Friday for San Diego County Valleys-Santa Ana Mountains and Foothills.

Heat Advisory until 9 PM PDT Friday for Orange County Inland Areas.


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