Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
212 FXUS66 KSGX 201047 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 347 AM PDT Fri Sep 20 2024 .SYNOPSIS... A low pressure system moving across southern California will bring a slight chance of mostly light showers this morning. There are greater chances for showers along with a chance of thunderstorms for this afternoon and early evening for southwestern San Bernardino and western Riverside Counties with the greatest potential for any heavier rainfall in the San Bernardino Mountains. For Saturday through Monday, dry with a warming trend with high temperatures warming to around 5 degrees above average for inland areas on Monday. Generally fair weather with seasonal temperatures will continue for Tuesday through Thursday, but with greater spread in the temperature guidance for the coast and valleys. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (Today through Sunday)... A closed low pressure system will move across southern California today and into Arizona tonight. It will bring some light showers from the coastal waters into the coast and valleys in San Diego County this morning. As the upper center moves eastward today, there is greater potential for showers along with a chance of thunderstorms to movement toward the southwest for this afternoon and early evening across southwestern San Bernardino and western Riverside Counties with the greatest potential for any heavier rainfall in the San Bernardino Mountains. Today will remain cooler with well-below average high temperatures, as much as 15 to 20 degrees below average for the mountains and inland valleys, with high temperatures for the Inland Empire mostly in the 70s. Dry weather with warming is expected for the weekend. On Saturday, greater warming is expected for the mountains and deserts with slower warming for the coast and valleys. Warming will continue on Sunday with the greater warming for the coast and valleys. With the warming, high temperatures on Sunday will return to around average with high temperatures for the Inland Empire in the mid 80s to mid 90s and for the lower deserts around 100. && .LONG TERM (Monday through Thursday)... The warming is expected to continue into Monday with high temperatures for inland areas around 5 degrees above average, mostly in the 90s for the Inland Empire and around 105 for the lower deserts. Generally fair weather with seasonal temperatures will continue for Tuesday through Thursday, but with greater spread in the temperature guidance for the coast and valleys. && .AVIATION... 200900Z...Coast to Mountain Slopes...Low stratus remain in place this morning, with the greatest coverage against the coastal mountain slopes, the eastern Inland Empire, and San Diego County hills/valleys, while the coastal basins are somewhat patchy. Bases are predominantly 3500-4500ft MSL, but intermittent CIGs around 1500- 2500ft MSL are possible at times until 16-18z, especially along the coasts. Clouds generally become SCT or less for most after 18z, while the coastal slopes may see higher coverage linger into the afternoon. Stratus rebuilds again between 03-06z this evening, with bases around 1500-2500ft MSL. Patchy, intermittent -RA or -DZ is possible along the coast and up against the coastal mountain slopes at times until 18-21Z Fri. Vis reductions of 4-6 SM and locally lower cigs possible in areas of - RA/DZ. From 20-02Z this afternoon/evening, there is a 25-45% chance of TSRA over the eastern Santa Ana Mtns and Inland Empire. Erratic winds, local up/downdrafts, and reduced vis in locally heavy rain expected near thunderstorms. Mountain Ridges to Deserts...Mostly clear skies with generally unrestricted VIS through the late morning. 50-60+% chance for RA and TSRA over the San Bernardino mtns, Riverside mtns, and High Desert 20Z-02Z this afternoon/evening. Erratic winds, local up/downdrafts, and reduced VIS in locally heavy rain expected near thunderstorms. && .MARINE... No hazardous marine conditions are expected through Tuesday. && .HYDROLOGY... A low pressure system moving across southern California will bring a slight chance of mostly light showers this morning. There are greater chances for showers along with a chance of thunderstorms for this afternoon and early evening to move southwestward across southwestern San Bernardino and western Riverside Counties. The greatest potential for any heavier rainfall is in the San Bernardino Mountains with rainfall of one-half to three-quarters of an inch possible with isolated hourly rainfall to one-half inch. The most likely location for any mud and debris flows from recent fires would be with the Line Fire in San Bernardino County. While much of the higher resolution guidance shows peak hourly rainfall rates to around one-half inch, there is greater spread in the timing of any heavier rainfall during the afternoon. Some of guidance has the peak earlier in the afternoon while some of the more recent HRRR guidance is later in the afternoon, toward 4 or 5 PM. The local NAM-bounded WRF from late Thursday afternoon had the earlier timing with peak hourly rainfall rates in the early afternoon. Since there`s been an overall slight slowly of this system over the last day or so, it will be interesting to see if there is a shift toward later in the afternoon with the next local WRF run from late Thursday evening that should be available in the next few hours. && .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...17 AVIATION/MARINE...Munyan