Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
157 FXUS66 KSGX 280423 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 930 PM PDT Thu Jun 27 2024 .SYNOPSIS... Slight cooling will occur in most areas Friday, with the greatest amount of cooling at night. A warming trend will occur this weekend and continue early next week, with excessive heat likely in the deserts again. With high pressure aloft continuing over the region, the excessive heat will likely continue most of next week in the deserts, with the high deserts of San Bernardino County having its highest temperatures the second half of next week with little change in the lower deserts. Otherwise, fair weather will prevail with night and morning coastal low clouds and patchy fog continuing, along with milder coastal conditions. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Skies were mostly clear this evening except for developing low clouds near the coast. The stratus will continue to develop overnight near the coast and extend into the San Diego County Valleys with the Inland Empire mostly staying clear. The late afternoon NKX sounding had precipitable water down to 1.33" from 1.73" 24 hours before, though 1.33" is still above average for late June. Regardless, impacts continue to be minimal from the moisture aloft, with only scattered afternoon cumulus over the mountains and no thunderstorms. Today was the first day since June 22 that we did not have a record high minimum (morning) temperature, and the next 2 nights will be near or just slightly above normal west of the mountains (as well as the day Friday, though with some warming Saturday), though days and nights will continue to be above normal in the deserts. The main weather impact for the next week will be the heat, mainly in the deserts, and with the expiration of the excessive heat warning at 8 PM this evening, we issued a new excessive heat watch for Sunday/Monday for the lower deserts. Current guidance has high confidence of increasing temperatures through the week in the high deserts, and some locations in San Bernardino County near Apple Valley/Victorville could approach 110 the second half of next week due to the East Pacific upper high building into California/Nevada and connecting with the west-east oriented southern US/northern Mexico upper high. Ensembles differ on the details after that, with some solutions sliding the upper high towards the interior desert southwest but other solutions keeping it overhead. Regardless, most solutions suggest temperatures 5-10 deg F above seasonal normals. From previous discussion... Pressure heights will continue to rise Sunday into Monday. Chances for 115 degree readings across the lower deserts increase to around 30-60 percent by this time per NBM. By Sunday, increased heat risk will not only be across the deserts but also most areas away from the coast. Highs in the near or above 100 degrees are likely for portions of the Inland Empire, with highs in the 90s across southern mountain areas and SD/OC valleys. Global ensembles are generally in agreement about high pressure building into area off the coast by the middle of next week, near 596-600 dm. This would continue the very warm conditions for much of the week for areas away from the coast. If this does occur, temperatures will continue to be 5 to locally 10 degrees above average. Confidence is moderate to high that temperatures will fluctuate minimally from day to day with warmer overnight low temperatures as we near the 4th of July holiday. && .AVIATION... 280400Z...Coast/Valleys...Marine layer building in at KSAN with OVC015 and tops ranging along the coast/valleys between 1500-2100ft MSL. Marine layer builds in through early Friday morning, with most coastal airports having BKN-OVC CIGs 1200-1500 ft MSL beginning between 05-07Z Friday. Localized VIS below 3SM in BR/FG possible in the coastal valleys overnight. Similar to Thursday morning, expecting marine layer scattering out beginning around 16-18z Friday. Synoptic pattern doesn`t look to change much for Friday evening as marine layer builds in once again beginning around 29/03z. Mountains/Deserts...Gusty northwest winds continue for parts of the Coachella Valley, ending by 28/06z. Light and variable overnight with SKC into Friday morning, with gusty west winds picking back up late Friday afternoon. Periods of strong gusts through mountain passes exceeding 40kts at times, and mod up/downdrafts possible in the vicinity, especially for low-flying aircraft. Some Cu possible over the mountains Friday afternoon, with bases likely at or above 15,000ft MSL. Gusty northwesterly winds pick back up in the Coachella Valley beginning between 28/20z-29/02z. Lowering VIS looks unlikely at this point, but periods of strong gusts may bring localized blowing dust. && .MARINE... No hazardous marine conditions are expected through Tuesday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Watch from Sunday morning through Monday evening for Coachella Valley-San Diego County Deserts-San Gorgonio Pass Near Banning. PZ...None. && $$ PUBLIC...Maxwell (Update)/APR (Previous Discussion) AVIATION/MARINE...Zuber