Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
683 FXUS66 KSGX 121619 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 915 AM PDT Sun May 12 2024 .SYNOPSIS... Night and morning low clouds and fog expected each night and morning for areas west of the mountains this week. Today is expected to be a few degrees warmer than yesterday, especially for inland areas. Slightly cooler conditions expected Monday and Tuesday. A few light showers may form over the mountains Tuesday and Wednesday afternoons. Seasonally warm weather is forecast Thursday and Friday. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... The marine layer was a little shallower on the 12Z sounding from KNKX compared to yesterday, but that did not stop the low clouds and fog from filling in the coastal basin overnight. Low clouds are expected to clear the valleys through the morning. The inversion on this morning`s sounding was about a degree stronger than yesterday`s and the onshore pressure gradient is trending more onshore compared to yesterday. Taking both of those factors into consideration, there is fairly low confidence in complete clearing at the beaches today. Further east, a few cumulus clouds may develop over the mountains this afternoon and clear skies are expected over the deserts. A weak ridge of high pressure has developed over California, which will result in warming conditions for inland areas. Highs today will be 4 to 8 degrees above normal for inland areas and there is a chance spots in the low deserts could reach 100 degrees for the first time this month. The ridge will shift east Monday as a weak upper level low approaches Southern California. This will result in slightly cooler conditions west of the mountains, but not much change in high temperatures for the deserts. The low slowly drifts into northern Baja through Wednesday, spreading slightly cooler conditions further inland to the deserts. The marine layer is also expected to deepen due to influences from the trough Wednesday. There is a small amount of mid-level moisture associated with this low, allowing for more cumulus clouds to develop over the mountain crests in the afternoon and perhaps an isolated shower or two over the highest peaks Tuesday and especially Wednesday. There is still some model uncertainty with how quickly the low moves east, with about 60 percent of ensemble solutions keeping the low over Southern California into Thursday. This would keep the marine layer deeper into Thursday. A ridge of high pressure begins to develop over the Eastern Pacific midweek, and will allow for some height rises and warming for inland locations as it tries to push the low east. There is fairly good agreement that the low will keep trekking east Friday allowing for further warming. This is short lived, however, as another closed low is forecast to develop off the So Cal coast, moving inland sometime next weekend. Still a lot of ensemble spread in the exact placement of these lows in the extended, so confidence in forecast temperatures remains on the lower side. && .AVIATION... 121600Z...Coast/Valleys...Low clouds will continue to retreat toward the coast through the morning. Confidence is moderate to high on cigs scattering after 18Z for coastal TAF sites. Cigs 1300-1800 ft MSL may locally stick near the beaches through the afternoon. Low clouds will push back inland near the coast and into the valleys between 01-03z Mon. Bases will be near 1000-1500 ft MSL, locally near 600 ft MSL. Confidence high on low clouds for lower elevations of SD/OC, moderate across the Inland Empire. Mountains/Deserts...Mostly clear with unrestricted VIS through tonight. SCT/BKN clouds over the mountains with bases around 9000 ft MSL Sunday afternoon. W winds increasing after 00Z Mon with surface gusts 20-35 kts, diminishing by 12Z Mon. && .MARINE... No hazardous marine conditions are expected through Thursday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...CO AVIATION/MARINE...APR