454 FXUS66 KSGX 110940 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 240 AM PDT Tue Jun 11 2019 .SYNOPSIS... Strong high pressure will bring very hot weather inland through Wednesday. Coastal areas will remain cooler with some low clouds and fog during the nights and mornings. Cooler weather will return the second half of this week as the high pressure breaks down. The marine layer will deepen during the second half of the week, spreading nocturnal clouds and cooler weather inland. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... The heat will be on again today as high pressure aloft peaks in strength over the southwest states. The heat will peak in the far inland valleys, mountains and deserts today, while the western valleys and inland coastal areas will begin a cooling trend as onshore flow increases. We followed all the model guidance Monday, which underestimated the offshore flow in the inland coastal and western valley zone. Hence, we underforecast the temps there. There is still a breath of offshore flow today, so having learned our lesson, we're forecasting max temps that exceed all the guidance for this inland coastal and western valley zone. Hopefully, the forecast max temps there will be more accurate. A heat advisory validates our confidence on this, but it is a bit unusual for all guidance to not capture the reality. Coastal low clouds will have random coverage again this morning, with patchy dense fog again for your morning commute near the coast. Look for almost identical coastal fog conditions for tonight into Wednesday morning and variable high clouds through Wednesday for all areas. Daytime high temps will be higher today than Monday for mountains and deserts, but a little lower west of the mountains. The strong upper high begins to break down Wednesday. That will allow the marine layer to deepen as a weak trough moves through California Thursday into Friday. Progressively cooler weather will march inland from the coast each day, but the lower desert will have to wait until Thursday before noticing any cooling. Mid-June average temperatures are forecast starting Thursday, before going a little below average thereafter. Strong onshore winds will develop Wednesday and Thursday evenings in parts of the mountains and deserts, where gusts will exceed 40 mph. A sort of amorphous trough pattern remains with us through the weekend at least, so coastal clouds will reach farther inland during the nights and mornings. Model solutions for next week diverge quite a bit, ranging from a persistent, regenerating trough to a strong ridge nosing into California from the Pacific. For now we'll keep the boat steered down the middle with a seasonal forecast until the models can work out their differences. && .AVIATION... 110900Z...Coast...Low clouds, with bases 500-800 ft MSL and tops near 1200 ft MSL, will continue through mid-morning. Areas of fog will lower VIS down to 1 SM at times, especially where low clouds intersect coastal mesas. Low clouds and fog are expected to clear by late this morning, around 17Z. Patchy low clouds may develop again late this evening with bases 500 ft or so, with patchy dense fog near the coast and a few miles inland. Otherwise, FEW/SCT high clouds through the period. Valleys/Mountains/Deserts...Mostly clear with unrestricted visibility through Wednesday. && .MARINE... Areas of dense fog and low visibility are expected over the coastal waters this morning. A Marine Weather Statement is in effect through noon today. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory from 10 AM this morning to 9 PM PDT this evening for Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Valleys- Santa Ana Mountains and Foothills. Excessive Heat Warning from 10 AM this morning to 8 PM PDT Wednesday for Coachella Valley-San Diego County Deserts-San Gorgonio Pass Near Banning. PZ...NONE. && $$ PUBLIC...MM AVIATION/MARINE...Brotherton