Strengthening high pressure over the southwest states will bring warming through Thursday with Thursday high temperatures 5 to 10 degrees above average for inland areas. There will be cooling of a few to around 5 degrees for Friday through Saturday, then not much change through early next week. The marine layer will mostly fluctuate between 1000 and 1500 feet deep with night and morning coastal low clouds spreading into portions of the western valleys late each night at time.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Evening update, Patchy low clouds are developing off the coast this evening, while areas of smoke and haze continue to push over the region due to ongoing wildfires. Latest runs of the HREF and local WRF show marine layer clouds and fog remaining fairly patchy for most of the night, filling in along parts of the coast by Wednesday morning. Ensembles have trended higher with PW in the low deserts Friday into the weekend, mostly due to forecast gulf surges with little change in mid-level moisture. Given the ridge axis will be overhead and the lack of instability, precipitation chances remain below 10%.
Previous discussion, A near 600dm area of high pressure over New Mexico will continue to strengthen Wednesday into Thursday, expanding westward over Southern California. This will lead to 850mb temperatures to near 30C, prompting temperatures to rise near 5 to 10 degrees above normal. The peak of the heat over the region will occur on Thursday. Nbm probabilities are moderate to high in seeing temperatures reach 105 degrees in central parts of the Inland Empire on Thursday and Friday and 115 on Thursday in the lower deserts. Please take precautions to beat the heat, such as staying in air conditioned places, taking breaks if having to work outside, and limiting outdoor recreation. As the high moves over the region, the marine layer will become shallower, leading to greater chances of fog for coastal areas and adjacent valleys over the next couple of mornings with visibility near one quarter of a mile at times. By Friday and Saturday, models show the placement of the high may be able to funnel low level monsoonal moisture into the lower deserts. Though this has a minute chance to bring any precipitation, an increase in humidity will make the heat feel even more oppressive as low temperatures in the lower desert will only lower from 80 to 90 degrees.
The area of high pressure is expected to retreat further to the east and weaken over the region by the weekend. This will lead to temperatures lowering back to seasonal averages with a deeper marine layer, though desert areas may see highs lower only a few degrees. Model ensemble guidance points to a growing ridge over the Pacific Northwest as the ridge over the Desert Southwest maintains its weaker strength, keeping us in a quiet weather pattern for the first half of next week. Differences in the forecast trends start to arise by the latter half of next week as as the interactions with the high near our area and a potential trough to the north lead to greater uncertainty.
060330z. Coasts/Western Valleys, Aside from a few patches of low clouds well offshore, VFR prevails this evening. These clouds will continue gradually to develop and spread inland by 09-11z Wednesday. However, there is a 40% chance that CIGs reach the coastal TAF sites by 06-08z. Regardless, these clouds will generally be based 500-800 ft MSL with tops around 1000 ft MSL. VIS reductions to 3-5 SM expected along the immediate coast and down to 0-2 SM over higher coastal terrain and western valleys, especially after 12z. These clouds/fog will scatter back out to the coasts by 16z Wednesday morning, with clear skies and VFR prevailing throughout the day.
.Inland Valleys/Mountains/Deserts, VFR conditions prevail through Wednesday evening.
Smoke from area fires, mostly the Gifford Fire in Santa Barbara County, will continue to be present at or above 10,000 feet MSL. Surface conditions hazy but still VFR.
No hazardous marine conditions are expected through Sunday.
Ca, Heat Advisory from 10 AM Wednesday to 8 PM PDT Friday for Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains- San Diego County Valleys-Santa Ana Mountains and Foothills.
Extreme Heat Warning from 10 AM Wednesday to 8 PM PDT Friday for Coachella Valley-San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
