Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
970 FXUS66 KSGX 230527 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 927 PM PST Wed Jan 22 2025 .SYNOPSIS... Critical fire weather conditions continue as Santa Ana winds and dry conditions continue into early Friday. Strongest winds are expected on Thursday. Single digit afternoon relative humidity values will occur through Friday afternoon. Shift in the weather is expected for the weekend, with increasing chances of rain and mountain snow. Some showers could linger into early next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Update: Latest high res model guidance displays that winds will continue to increase overnight across the higher terrain, with gusts occasionally approaching 50 mph. These will eventually mix down to the lower elevations tomorrow by late morning for the inland valleys, and eventually to the coastal areas by early afternoon. Winds with this Santa Ana event will not be as strong as the previous event earlier in the week, although the dry airmass in place is still yielding RH values in the 5 to 10 percent range across most of the CWA. By Friday morning, the strong and gusty winds appear to be mostly confined to the higher elevations, although it will still be very dry, with minimal RH recoveries of 15 to 20 percent overnight. The major change looks to be by later in the evening on Friday when the onshore flow becomes predominant and advects in much cooler and moist air, and essentially replaces the drier air. There will be increasing lower level moisture from then on going into Saturday, with the chance of precipitation increasing as an upper level low develops over central California and then makes its way southward over SOCAL moreso towards the evening hours. Given that there will be a core with colder air aloft with this and just enough instability as a result, and isolated thunderstorm or two cannot be ruled out, especially over the mountains. This will also drop down snow levels to the 3000 ft elevation by later in the evening on Sunday. Please keep this in mind if you plan on traveling this weekend through the mountain passes, such as Cajon Pass, as there will likely create some impacts to travel for these locations. Some snow will also be possible for the high deserts in San Bernardino County. (Previous discussion submitted at 148 PM) Through tonight there will be northeast winds of 20 to 30 mph with gusts to 45 to 55 mph along and below the coastal slopes of the mountains. Winds will increase for Thursday, with northeast winds of 30 to 40 mph with gusts to 60 to 75 mph and with isolated gusts to 85 mph for the San Diego County mountains. Winds will slowly decrease into Friday morning. Overnight humidity recovery will be poor Thursday night into Friday, with relative humidity only reaching 15 to 20 percent for inland locations. Lowest daytime humidity will fall to around 5 percent Thursday afternoon and around 5 to 10 percent on Friday afternoon. A few degrees of cooling is expected for Thursday away from the coast. Then cooler on Friday for coastal areas with the mountains a few degrees warmer. An upper level low pressure system from the north will move into central California on Saturday. The low will slowly move southward into Southern California by Sunday or Monday. Most of the uncertainty in the model ensemble solutions surrounds the timing of the low, with lesser uncertainty in the amplitude of the low. Most of the ensemble solutions for Sunday and Monday (80 and 75 percent respectively) keep the low more to the west which would be a favorable track for precipitation across the area. Current forecast keep precipitation chances through Tuesday. Through Tuesday night there is a 50 to 70 percent chance of one-quarter inch or more of precipitation for the coast and valleys, with an 80 percent chance of one-quarter inch or more of rainfall/liquid-equivalent in the mountains. In the mountains there is a 30 to 40 percent chance for three-quarters of an inch or more of rainfall/liquid-equivalent. Current forecast has the highest and most widespread chances of rain Saturday night into Sunday. This is expected to be a cold system with snow level of 4000 to 5000 feet on Saturday afternoon will fall to around 3500 to 4000 feet on Sunday. Current forecast keeps the snow level 3500 to 4000 feet through Tuesday. Ensemble guidance is indicating that snow could accumulate in the High Desert, with multiple members of both the ECMWF and GFS showing some amount of accumulating snow although there is a wide range of solutions when it comes to how much snow will accumulate. NBM chances for 12 inches or more of snowfall in the mountains for the weekend is around 80 percent for elevations above 7000 feet. There remains uncertainty in the forecast for early next week. Much of the uncertainty surrounds the timing of how quickly the low pressure system will depart to the east. Due to the cold nature of the system, below average temperatures are forecast for Saturday through Wednesday. By Wednesday most ensemble solutions have the low to our east with a ridge of high pressure building over the West Coast of the US. && .AVIATION... 230430Z....FEW-SCT high clouds will gradually decrease overnight. Areas of northeast winds/gusts of 25-35 kts continue overnight, mainly in the mountains and adjacent foothills/valleys, generating areas mod up/downdrafts in lee of mountains. Strong winds (25-30 kts) within 2000ft of the surface will persist in coastal Orange County, leading to the potential for LLWS at KSNA. East to northeast winds strengthen and become more widespread early Thursday morning, peaking early Thursday afternoon with gusts 30-45 kts, locally 50-60+ kts in mountains and adjacent foothills/valleys. Winds gradually subside Thursday night into Friday morning. NWS San Diego is aware of limited communications of observations from KTRM since January 8th. We are working with the FAA to address this issue. && .MARINE... Offshore winds become breezy late tonight through Thursday evening. Occasional gusts near 20 kts are possible. There is a slight chance of thunderstorms late Saturday associated with a regional storm system. Any thunderstorms could produce locally gusty, erratic winds and briefly hazardous conditions. Otherwise, prevailing winds and seas are not expected to generate hazardous marine conditions through Sunday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Red Flag Warning until 10 AM PST Friday for Orange County Inland Areas-Riverside County Mountains-Including The San Jacinto Ranger District Of The San Bernardino National Forest-San Bernardino County Mountains-Including The Mountain Top And Front Country Ranger Districts Of The San Bernardino National Forest-San Bernardino and Riverside County Valleys -The Inland Empire-San Diego County Inland Valleys-San Diego County Mountains-Including The Palomar And Descanso Ranger Districts of the Cleveland National Forest-San Gorgonio Pass Near Banning-Santa Ana Mountains-Including The Trabuco Ranger District of the Cleveland National Forest. High Wind Warning from 6 AM to 6 PM PST Thursday for Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains- San Diego County Valleys-San Gorgonio Pass Near Banning- Santa Ana Mountains and Foothills. PZ...None. && $$ UPDATE...STEWEY PUBLIC...CO AVIATION/MARINE...PG