Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
594 FXUS66 KSGX 220501 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 901 PM PST Thu Nov 21 2024 .SYNOPSIS... Warm and dry weather will continue through Friday. An atmospheric river associated with a Pacific storm impacting northern California will slide south and arrive Saturday but weaken considerably. A second surge of moisture will develop over the eastern Pacific associated with the upper trough in place and bring additional precipitation Sunday night through Tuesday night. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Clear skies over the region but some marine low clouds are expected in patches near the San Diego coast late tonight. A warm day away from the beaches. Air mass 15 to 17C at 850 mb level after the recent weak Santa Ana winds and result of upper ridging ahead of the large storm in the east Pacific producing large rainfall amounts in Norcal, which continues. Similar weather on Friday, warm and dry, though we start to cool further on the coast. The second Norcal atmospheric river is forecast to slide across Socal on Saturday, but weakening wind speeds and moisture transport since the energy, and cold air for instability from the Pacific storm stays to the north and offshore. This will result in light stratiform precipitation late Saturday into Sunday morning and tapering off on Sunday, with main orographic enhanced on the front south facing slopes of the San Bernardino mountains. A second wave from the main Pacific upper low pulls another atmospheric river surge into Socal for Sunday and Monday. This has little better potential especially for San Bernardino mountains. This west to east surge of moisture is slow to exit on Tuesday and may linger into Wednesday, though providing light rain south of San Bernardino mountains. Overall light rain from 3 periods of precipitation and high snow levels indwell above 8500 feet finally come down by late Tuesday with the upper trough and colder air dropping into Socal, but possibly not lower than 7000 feet MSL by Tuesday night and Wednesday morning with the remnant and weakening upper low passing over Central California. && .AVIATION... 220430Z...Coasts...Mostly clear skies prevails, but patchy coastal low clouds (likely based around 700-900ft MSL) are expected to develop early Friday morning around 10-12z. KSNA has the best chances for CIGs after 12z (65-70%), with about a 50% chance for CIGs at KSAN, and only 35-40% chance for KCRQ. The clouds will still be somewhat patchy, and CIGs could come and go at times. Widespread VIS restrictions aren`t expected, though intermittent VIS less than 3SM is possible where clouds intersect coastal mesas and higher terrain. Any clouds look to scatter out offshore around 17-18z, giving way to mostly clear skies. Low clouds should push back ashore Friday evening around 00-03z, with likely higher bases and more inland extent. Valleys/Mountains/Deserts...Mostly clear skies, relatively light winds, and unrestricted VIS expected through Friday evening. && .MARINE... No hazardous marine weather conditions expected through Tuesday. && .HYDROLOGY... Light rainfall from 3 periods of precipitation Saturday afternoon through Wednesday. High snow levels do not drop until late Tuesday. Due to the weakening atmospheric river Saturday and the second surge of moisture from west to east Sunday night through Tuesday night, favored from slopes of the San Bernardino mountains from Crestline to San Gabriel mountains could reach totals of 1 to 2 inches of rain with amounts dropping over to the south rapidly to under 0.50 inches. Traditional climate gradient or more rainfall for LA Basin versus San Diego. The intensity of the rainfall should limit impact to the 3 large burn scars but will need to be monitored. && .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...Tardy AVIATION/MARINE...Munyan