Gradual cooling through the weekend with a return of marine layer low clouds and fog at the coast. Even with the cooling, temperatures will remain 15-25 degrees above normal into next week, highest on Wednesday during the next peak in the heat.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
At the risk of sounding like a broken record, numerous monthly and daily record highs were broken again today. In fact, of our climate sites that reported to day, all but two (Newport Beach and San Diego) broke or tied their daily record. Nine sites broke or tied monthly records that were set earlier this week. See the Record Event Report headlined on our homepage at weather.gov/sandiego for more details. While the days of monthly record high temperatures is behind us, several daily high temperature records are forecast to be broken or tied every day for the next week.
Patchy low clouds are along the coast of Baja California around 15 mi south of the border, but aren't making much northward progress. Some low clouds and fog may develop along our coasts tonight into Saturday morning, but confidence is low in where fog will develop and how long it will last.
The upper level high currently centered over western AZ will continue to shift east and weaken this weekend in response to a series of short wave troughs moving into the Western US. This will allow for some cooling and stronger onshore flow this weekend. For the mountains westward, HeatRisk will fall to minor to locally moderate, and the Heat Advisory was allowed to expire for the coastal areas, valleys, and mountains. The Extreme Heat Warning for the low deserts remains in effect through 8 PM Saturday as temperatures there remain well over 100 degrees. The weak troughing and stronger onshore flow will also help the marine layer rebuild, with more widespread low clouds and fog along the coast Saturday night into Sunday morning. The marine layer deepens slightly the following night, with the potential for dense fog on the coastal mesas by Monday morning.
The upper level ridge begins to rebuild over So Cal on Monday for minor warming. The warming trend continues into Wednesday as the ridge strengthens and moves eastward. By Wednesday highs will rise to around 15-25 degrees above normal. The ridge begins to weaken and progress eastward through the latter half of the week, though the degree to which both of these occur is still uncertain. Around 29% of the global ensemble members keep the ridge further west, maintaining warmer weather even into the end of the week, while the remaining members have the ridge axis closer to the Plains and weak troughing beginning to develop of the West Coast for better cooling. Still no precipitation chances in sight through the end of next week.
210000z, Mostly clear skies and VFR conditions expected through 06Z. Patchy fog based 100-400 ft MSL with vis 1/2-3 SM expected to begin moving into the SD coast after 06Z, then into the OC coast after 09Z. Low clouds likely won't move any further than about 5 miles inland overnight. 30-40% chance for vis less than 1/2SM at coastal sites overnight. Fog clears to beaches 15-17Z. Elsewhere, VFR conditions through the TAF period.
Patchy fog with visibility under 1 nautical mile is expected to move over the coastal waters this evening and overnight, highest chances near the coastline. Otherwise, no hazardous marine conditions expected through Wednesday.
Ca, Extreme Heat Warning until 8 PM PDT Saturday for Coachella Valley-San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
