Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
669 FXUS66 KSGX 210409 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 909 PM PDT Thu Jun 20 2024 .SYNOPSIS... A warming trend will continue through Saturday with high temperatures on Saturday as much as 5 to 10 degrees above average. A shallow intrusion of lower level moisture for the lower deserts will bring warmer nights with days not quite as hot for the weekend. There is also a slight chance of showers and thunderstorms when mid level tropical moisture arrives this weekend. Then drier and continued hot inland for Monday through Thursday. Hottest days in the deserts will be from Monday to Thursday. The marine layer will continue to keep areas near the coast cooler but less extensive marine layer coastal clouds especially during the weekend and slowly returning during the heat wave next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .Evening Update... Today was the last day with temperatures near to below seasonal norms for our inland locations who saw temperatures with highs mostly in the 70s and 80s along and west of the mountains, and at or below the 110 degree mark across the lower deserts. The thin marine layer also kept many coastal areas clear making for a beautiful day near the beaches. Low clouds are slowly beginning to reform near San Diego this evening. Latest HREF model guidance hints at most coverage staying near coastal San Diego County, with less likelihood of any major cloud coverage across Orange County. The area of high pressure across the Southeast and Southern Plains of the country will slowly expand westward Friday into the weekend and warm the area up to above seasonal averages. All eyes turn toward this weekend as moist southerly flow and instability make an appearance which has the potential to provide chances for thunderstorms. Sunday looks to be the peak of the intensity, so POP forecast from this afternoon is sufficient. This warm air mass will provide not only warm days but also warm nights. Raised nighttime temperatures slightly across mountains and high deserts for Saturday and Sunday nights. Otherwise, minimal changes in the forecast for this evening. .Previous Discussion... The heat wave begins on Friday and peaks on Saturday for coast and inland valleys as 500 mb heights rise. 500 mb heights rise to 594 DM this weekend and hold through next week, but the main difference this weekend is large tropical moisture surge around the upper ridge. This arrives from the south Saturday and lingers into Sunday along with low level moisture surge into the lower deserts. There is sufficient instability and upper level wave so there is a threat for elevated convection this weekend, then this becomes more surface based and focused on the mountains and deserts slopes on Sunday and may linger with isolated cells on Monday. The threat includes the coastal areas and marine open waters where precipitable water as high as 2 inches arrives Saturday night. The heat advisory remains for the inland valleys and mountains and the heat watch for more severe heat and major risk remains in effect for the deserts Monday to Thursday for prolonged heat wave and highs 110 to 115F and increasing overnight warm lows. Hottest day is Saturday before mid level moisture arrives. For late June over 110F becomes critical for lower deserts and this is along a long duration before the upper ridge weakens temporarily late next week. Hottest day for deserts looks to be Tuesday and Wednesday under the 594 DM 500 mb heat dome (upper ridge) across Socal. && && .MARINE... A system moving by to the south may bring showers Saturday through Monday, but current guidance suggests that the thunderstorm risk is minimal. Otherwise, no hazardous weather is expected through Wednesday. A Marine Weather Statement has been issued to cover this hazard. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory from 10 AM Saturday to 8 PM PDT Sunday for Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire. Heat Advisory from 10 AM to 8 PM PDT Saturday for Riverside County Mountains-San Bernardino County Mountains-San Diego County Mountains-San Diego County Valleys. Excessive Heat Watch from Monday morning through Wednesday evening for Coachella Valley. Excessive Heat Watch from Saturday morning through Thursday evening for San Diego County Deserts. PZ...None. && $$ PUBLIC...APR AVIATION/MARINE...Maxwell