Widespread moderate with areas of major HeatRisk will continue through Friday. HeatRisk will decrease for the weekend, with minor cooling. Even with the cooling, temperatures will remain above average into next week. Patchy marine layer low clouds and fog will be present at times, most likely to impact the coastal waters and immediate coast.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Evening update, Numerous daily and monthly high temperature records were broken or tied again today, including Idyllwild which broke their monthly high temperature for the third day in a row with a high of 90 degrees. Indio and Thermal tied the national high temperature record for March with a high of 108 degrees.
Patchy low clouds and fog have developed just off the coast of far southern San Diego County again this evening but have yet to make it over land, though satellite imagery is showing it nearing Point Loma. Occasional dense fog is possible at the beaches from about Solana Beach southward tonight into early Friday morning. The large upper level high currently centered over the lower Colorado River Valley will shift eastward and weaken slightly on Friday, allowing for very minor (1 to 2 degrees) cooling west of the mountains with little change in the deserts.
Previous discussion, Through Friday widespread temperatures in the 90s to low 100s expected for the inland valleys, with highs in the mid- 80s to low 90s for coastal areas away from the immediate coast and the lower elevations of the mountains. In the low deserts, highs will likely exceed 105 degrees in most locations through Saturday. Chances for exceeding 110 degrees on Friday are 60 percent for Indio, 20 percent for Palm Springs, and 10 percent for Borrego Springs. In the High Desert, temperatures will be in the mid-90s.
Weakening high pressure aloft and strengthening onshore flow will bring 4 to 8 degrees of cooling Saturday. That will be most noticeable for locations west of the mountains, but even the deserts will cool 3 to 5 degrees. A weak low pressure system aloft will move east through Southern California into the Great Basin sometime Sunday or Monday. That will bring an uptick in westerly winds Saturday, which have the potential to turn weakly offshore by Sunday afternoon into Monday morning. Ridging aloft looks to rebuild Monday and strengthen into the middle of the week. This ridge isn't expected to be as strong as the one over Southern California this week, but it will be enough to maintain above average temperatures through next Thursday. Widespread minor with areas of moderate HeatRisk will be present in the valleys and low desert for much of next week.
With the ridge axis shifted further east today, weak onshore flow has returned to coastal areas. The weak onshore flow was enough to allow patchy dense fog along the immediate coast this morning. Areas of patchy dense fog over the water and at the coast is possible each morning through Saturday. With the aforementioned passing weak low pressure onshore flow will briefly increase, making chances of dense fog less likely for Sunday morning. Low cloud and fog coverage on Sunday morning may reach into the western valleys. Weak offshore flow early next week may keep low clouds and fog patchy and more confined to the immediate coast again.
200030z, Patchy low clouds based less than 500 ft MSL are expected to surge over the waters of southern SD County 02-04z this evening and slowly develop off of the rest of the coastline in patchy fashion after 04z. Likely timing VCFG for KSAN around 03z and KCRQ around 05z, bringing slight chance for intermittent impacts. FG starts moving into coastal areas 06-08z, bringing higher chance for patchy cigs below 500 ft MSL and vis < 1 SM. 60% for VIS below 1SM at times at KSAN and 40% for KCRQ. Greater uncertainty for KSNA with a slight (30%) chance for VIS/cig reductions mainly after 13z Fri. Clearing 15Z-17Z. Everywhere else, VFR conditions expected through the TAF period.
Patchy fog is expected to surge from the south this evening, lowering visibility to less than 1 NM locally. Visibility improvements expected mid-morning Friday. Otherwise, no hazardous marine conditions are expected through Tuesday.
Ca, Heat Advisory until 8 PM PDT Friday for Orange County Coastal Areas-Orange County Inland Areas-Riverside County Mountains- San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Coastal Areas-San Diego County Mountains-San Diego County Valleys-Santa Ana Mountains and Foothills.
Extreme Heat Warning until 8 PM PDT Saturday for Coachella Valley-San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
