445 FXUS66 KSGX 112037 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 137 PM PDT Sun Apr 11 2021 .SYNOPSIS... Cooling will intensify Monday and Tuesday in response to a low pressure system developing over the northern Great Basin. This will enhance onshore flow across the region, bringing gusty winds to desert slopes and passes Monday through Wednesday (strongest Tuesday), and a deeper marine layer. The latter should be sufficient to generate some sprinkles across the coastal basin Monday night into early Tuesday morning, and possibly again Tuesday night, with minimal accumulations expected. Thursday will see us return to a warming trend that will continue into the weekend, with shallower marine layer clouds each night/morning at the coast. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... High clouds are abundant today, shielding us from brighter skies and keeping temperatures a little more in check compared to previous days. It's relatively mild nonetheless, with inland areas (especially the mountains and deserts) still a few degrees above normal. Low clouds will again fill the coastal basin tonight, extending far into the valleys as a coastal eddy and tightening onshore pressure gradients force some deepening. With a low pressure system dropping southward toward the northern Great Basin Monday into Tuesday, below normal temperatures will finally make a return. Gusty west winds will follow suit, impacting desert slopes and east-west facing passes through Wednesday, and peaking on Tuesday when they'll likely reach advisory levels with gusts 35 to 50 mph, locally higher. By Monday night, the marine layer will have deepened enough to allow for patchy drizzle or brief light showers across much of the coastal basin and into the windward mountain slopes. Accumulations, if any, will be light and measured in hundredths of an inch, tapering off in the morning. A similar scenario may play out Tuesday night into early Wednesday morning. Tuesday and Wednesday will be similarly cool, with highs that will struggle to reach 70 anywhere outside of the deserts. And that, folks, will be the extent of this teaser. It will be a welcome change for many, bringing pleasantly cool temperatures for hiking, though certainly not ideal beach weather. Our vegetation would certainly appreciate some meaningful precipitation as we inch closer to the climatological end to our rainy season (and also an almost guaranteed early start to high fire season), but that's not on the table as it stands. As the Great basin low dissipates, zonal flow will gradually transition to weak riding as we near the weekend. Temperatures will begin to warm starting Thursday, and the warming trend will last through at least Sunday, by which time we should return to warmer than average conditions as highs in the 80's make a comeback to the interior. Coastal low clouds will continue each night and morning, but will be considerably shallower during the latter half of the week. && .AVIATION... 112030Z...Coast/Valleys...Patchy low clouds with bases 1300-1600 feet MSL will continue near the immediate coast this afternoon with most vis 6+ miles. Areas of stratus will develop again this evening, mostly 01Z-05Z Mon and extend into many valleys after 07Z Mon with bases 1200-1800 ft MSL and tops to 2200 ft MSL with higher terrain obscured. Local vis 1-3 miles will occur in the valleys 07Z-16Z Mon. Otherwise, mostly BKN clouds at/above 20000 ft MSL will prevail this afternoon, decreasing tonight and Mon morning. Mountains/Deserts...Mostly BKN clouds at/above 20000 ft MSL will prevail this afternoon, decreasing tonight and Mon morning with unrestricted vis. && .MARINE... Breezy west-northwest wind gusts to 20 knots will occur each afternoon and evening in the outer waters through Monday. Strongest winds will be near San Clemente Island. Otherwise, no hazardous marine weather is expected through Friday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ SYNOPSIS/PUBLIC DISCUSSION...Rodriguez AVIATION/MARINE...Maxwell