Marine Weather and Tide Forecast for Costa Mesa, CA

DISCUSSION
FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

Foggy conditions are present along the coast and into valleys to about 10-15 miles inland this morning, and many weather stations are reporting visibility between a quarter mile and 3 miles under the stratus deck. This morning's sounding combined with local pilot reports reveals a saturated layer 1000-1200 feet deep.
Typically when the marine layer makes it inland like this, visiblity improves as you approach the coast, but the deeper cloud layer has prevented major improvements.

Between the deep cloud layer, the strong inversion present this morning, and the shallow saturated layer present at the bottom of the inversion that can be seen on the sounding, the cloud layer will be later than average in retreating to the coast and will likely stick around for parts of the beaches through the early afternoon. Inland areas in San Diego County have been clearing fairly well, but clouds appear more stubborn along SD coastal areas and for most of Orange County.

While the coastal cloud layer will result in cool temperatures this afternoon similar to yesterday's, areas just inland are starting a warming trend today, with afternoon high temperatures 2-6 degrees warmer today than yesterday. Otherwise, locally breezy offshore winds will continue today and tomorrow through parts if the mountains as well as areas south of the Cajon Pass and through and west of the Banning/San Gorgonio Pass. Peak gusts are generally 20-30 mph, with local gusts to around 40 mph.

PREVIOUS DISCUSSION
224 AM PST Mon Dec 15 2025...
With a slightly deeper marine layer this morning, the dense fog is not as widespread as it has been previously. Still, pockets of dense fog can be expected on higher coastal mesas and western valleys this morning, so be aware and plan accordingly, especially if you travel on the 91 or 241 in OC into Riverside County or the 15 in San Diego County. Otherwise, look for another sunny and warm day, especially away from the coast.

Offshore flow will increase a little today, producing localized northeast winds through Tuesday morning in the usual foothill areas through and below mountain passes. Isolated top gusts could reach 30-40 mph. This offshore flow will push back on the marine layer, reducing coverage of coastal clouds and fog for tonight and Tuesday morning.

Our large scale weather pattern features a strong, active zonal flow, which has brought and will bring heavy rain to WA, OR. The next shortwave through that region will help turn flow here in SoCal briefly onshore Tuesday night and Wednesday, bringing back more coastal fog and also briefly boosting winds in the mountains and deserts, particularly the high desert late Wednesday. The flow trends offshore again Wednesday night and Thursday before turning weakly onshore again Friday. This time the onshore flow appears to remain for the weekend and beyond, with coastal clouds probably reaching into some valleys nights and mornings. Temperatures will fluctuate, especially west of the mountains, as the surface flow oscillates from onshore to offshore and back again. Right now Tuesday and Thursday look like the warmest days in the coming week, with high temps inland reaching 15-20 degrees above average for this time of year, and 5-10 degrees above average at the coast. Even the cooler days this week will continue well above average regionwide.

That zonal jet stream to our north will slowly but steadily sag southward next week, tapping into some subtropical moisture along the way. Confidence is understandably low in any forecast that far out, but if the majority of current ensemble solutions are right, SoCal would get some rain by the time Santa Claus arrives.

AVIATION
151630Z
Coast/Valleys
Currently low clouds based 200-500 ft MSL over the coast stretching inland 15 SM with BR/FG visibilities 1/4-1 1/2 SM. Clouds and fog should start clearing out around 17-18Z for San Diego County and after 19-20Z for Orange County. Low clouds with bases around 100-500 ft MSL and BR/FG with visibilities 1/4-3 SM are expected to return this evening after 02-03Z for the San Diego coast and after 05-06Z for Orange county. Low clouds and fog will be much patchier in nature than this morning.

Mountains/Deserts...Clear skies and VFR conditions expected through the TAF period.

MARINE
Low clouds will bring areas of low visibility around 2-5 NM through the early afternoon. Seas will rise briefly to 5 to 7 feet in the outer waters Wednesday afternoon through late Thursday. Otherwise, no hazardous marine conditions are expected through Friday.

SGX WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...None.