593 FXUS66 KSGX 010408 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 808 PM PST Fri Jan 31 2020 .SYNOPSIS... Building high pressure aloft will continue warmer weather into Saturday with well above average temperatures. An incoming trough will bring strong southwest to west winds and a chance of light precipitation late Sunday into Monday, along with much cooler weather. A Santa Ana pattern will set up late Monday through Tuesday, bringing gusty offshore winds to the mountains and deserts, and warmer weather for the latter half of the week. A pattern change may be in store next weekend, bringing much cooler weather and possible precipitation. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... A High Wind Watch has been issued for the mountains and deserts from late Sunday afternoon through Monday morning. Southwest to west winds of 30 to 40 MPH with gusts of 60 to 75 MPH will be possible. Another forecast update has been issued. At 8 PM PST, skies were mostly clear over SoCal. Just a few high clouds were drifting south over the region. Moderate offshore sfc pressure gradients were holding from SW NV to KSAN, supporting local NE wind gusts 20-30 MPH in those wind-prone areas. After a warm day, temperatures remained elevated this evening in many areas. Dewpoints are lower through, and with clear skies and weaker winds, temps should fall quickly later tonight. Still, look for an even warmer day on Saturday as a strong ridge axis moves overhead keeping skies mostly clear, and weak offshore flow and very dry air responds sharply to the early February sun. Temperatures have been bumped up on Saturday a few degrees in the latest updated forecast. A fast-moving Pacific trough will move through on Sunday and Monday, resulting in strong southwest to west winds in the mountains and deserts, and a chance for light precipitation. Strongest winds will occur on the desert slopes of then mountains and locally into the deserts with peak gusts of 60 to 75 MPH possible whit some mountain wave activity possible. Deterministic and ensemble model solutions show very little precipitation over the region Sunday night into Monday. Nevertheless, a few hundredths of an inch could fall west of the mountains, and around 0.10 to 0.15 of an inch in the mountains Sunday night through Monday morning. A dusting of snow is possible as well with snow levels falling below 4000 FT. It will be much colder in the wake of the trough, with daytime highs anywhere from 5 to 15F below average Monday and Tuesday. Some frost could occur in the eastern valleys of San Diego County Tuesday morning as lows dip into the mid 30s. A surface high will settle in over the Great Basin late on Monday, placing us back into a Santa Ana wind pattern Monday and Tuesday, with the strongest offshore winds on Tuesday. High pressure will rebuild over the West Coast on Wednesday, bringing a warming trend through Friday. Additionally, weak onshore flow could bring some marine layer clouds and fog to coastal areas Thursday night into Friday morning. Deterministic and ensemble solutions from both the ECMWF/GFS models are hinting at a deep trough developing along the West Coast next weekend, bringing us a chance for precipitation and cooler weather. It is still too far out to know the strength and exact timing, but it could be a significant pattern change. && .AVIATION... 014000Z...Mostly clear skies with unrestricted vis will prevail through Saturday evening. && .MARINE... Strong northwest winds will arrive late Sunday afternoon, peak Sunday night and gradually diminish Monday. Gusts of 35 to 40 knots will be possible in the outer coastal waters and 25 to 35 kt gusts possible for the inner waters. A Gale Watch remains in effect for 2 PM Sunday through 2 PM Monday. A short-period very large west- northwest swell will be accompanied with these winds and generate large combined seas of 14-18 ft in the outer waters and 9-13 ft in the inner waters along with and steep waves. && .BEACHES... Elevated surf of 4-6 ft will likely occur Sunday night and Monday as a large, short period swell from 290-295 degrees develops && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...High Wind Watch from Sunday afternoon through Monday morning for Apple and Lucerne Valleys-Coachella Valley-Riverside County Mountains-San Bernardino County Mountains-San Diego County Deserts-San Diego County Mountains-San Gorgonio Pass Near Banning. PZ...Gale Watch from Sunday afternoon through Monday afternoon for Coastal Waters from San Mateo Point to the Mexican Border and out to 30 nm-Waters from San Mateo point to the Mexican Border Extending 30 to 60 nm out including San Clemente Island. && $$ PUBLIC...10 AVIATION/MARINE/BEACHES...SS