Area Forecast Discussion
Issued by NWS San Diego, CA

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280 FXUS66 KSGX 242020 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 120 PM PDT Sat Jun 24 2017 .SYNOPSIS... High pressure aloft will continue the hot weather far inland this weekend, while a marine layer and onshore flow keep coastal and western valley areas mild, with periods of nocturnal low clouds and fog. High pressure aloft will weaken and move to the south next week as a pair of low pressure systems move inland to the north through Wednesday. This will deepen the marine layer and drop high temperatures to average or below for late June. Strong rip currents and higher than normal tides will prevail into this evening. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Satellite imagery this afternoon showed marine stratus continued offshore and at some beaches, but clearing was more complete than earlier thought. Over the mts, towering cumulus clouds had developed over portions of the Riverside and San Bernardino County Mts..... Surface pressure gradients to our local deserts were 5-9 MBS onshore. Peak wind gust reports around midday have been in the 25-35 MPH range near the passes, otherwise well below 25 MPH. Based on the cumulus development, it appears there is a small chance for a lightning strike or two over the San Bernardino Mts before sunset. The RAP13 shows isolated, elevated cape values in the mid- levels at around 120 J/K over the San Bernardino Mts through 01Z, but winds and moisture to support even scattered development appear lacking. At this time...POPs are below 10%, however there is a chance for a dry lightning strike or two before sunset along the higher terrain. The high pressure ridge over the SW will maintain through Sunday, then weaken and slip westward to reemerge stronger again over the EastPac along 145W. At the same time, a cut-off low off the CA Coast near 135 W, will weaken and ride the top of the ridge inland toward the PacNW. Another weak shortwave will follow from the NW and reinforce the troughing over the West through midweek. These events will suppress heights/thickness over SoCal and much of the SW, and increase the onshore flow and the marine layer depth, resulting in cooler weather. In the meantime, several models and MET/ECMWF MOS guidance indicate a thinning of the marine layer through Mon as a stronger low-level NW flow develops over the CA Bight. Other factors such as falling heights, a weak shortwave trough moving overhead, and sfc-pressure falls over the Great Basin suggest maintaining the marine layer depth. Perhaps that will occur, but clouds may be still be more limited. In any case, that is about our only forecast issue for the next several days. For the latter half of next week there is little height/thickness recovery over the SW, but onshore flow weakens a bit so the marine layer may decrease again, resulting in modest temp gains again into next weekend. && .AVIATION... 241955Z...Coast/Valleys...Through 25/0000 UTC, primarily P6SM vis and FEW-SCT clouds AOA 15000 ft msl, except at and near the beaches where BKN clouds 1000-2000 ft msl are likely to linger. 25/0000-1500 UTC, stratus re-developing and moving inland 10-15 sm, with bases around 300-700 ft msl, tops around 1200-1700 ft msl, areas of vis 2- 5 sm, and local vis down to around 1/4-1/2 sm along higher coastal terrain/inland mesas. Confidence in cig heights/vis is low. Mountains/Deserts...BKN-SCT cumulus clouds with bases around 10000 ft msl over the mountains will continue through 25/0000 UTC, with just the slightest risk of a lightning strike or two. These clouds dissipating after 25/0000 UTC. Otherwise, FEW-SCT AOA 15000 ft msl and P6SM vis continuing through Sunday morning. && .MARINE... Northwest wind gusts over the outer waters may reach 20-25 kt during the afternoons and evenings Sunday through Tuesday, potentially resulting in conditions hazardous to small craft. && .BEACHES... High tides will reach 7+ ft again this evening. Tides this high may result in minor tidal overflow at low lying beaches. The Beach Hazards Statement continues through 11 PM this evening. High tide will fall below 7 feet Sunday, lowering the tidal overflow threat. && .FIRE WEATHER... Heat and gusty winds along the ridges, desert slopes and passes will create a heightened risk of wild fire spread late today into the evening and again on Sunday. There is also a small chance for isolated dry lightning strikes in the San Bernardino Mts into early evening. Drier air aloft will preclude any threat of convection over the mts on Sunday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Excessive Heat Warning until 9 PM PDT Monday for Coachella Valley-San Diego County Deserts-San Gorgonio Pass Near Banning. Heat Advisory from 10 AM to 9 PM PDT Sunday for Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains-Santa Ana Mountains and Foothills. Excessive Heat Warning until 9 PM PDT Sunday for Apple and Lucerne Valleys. Beach Hazards Statement through this evening for Orange County Coastal Areas-San Diego County Coastal Areas. PZ...NONE. && $$ PUBLIC...JAD AVIATION/MARINE/BEACHES...Harrison

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