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August 4, 2020 – Gradual cooling returns today and continues through Thursday. Warmer weather returns for the weekend.

Discussion

Clear skies cover the region early this morning. IR difference imagery shows stratus has returned to the coast with profiler data indicating the marine layer has deepened to around 1000-1500 ft. Onshore surface pressure gradients are trending onshore, and a moderate Delta Breeze has returned to Travis AFB. Elsewhere, winds are generally on the light side. Current temperatures are mostly within a few degrees of what they were 24 hours ago and range from the mid 40s in the colder mountain valleys, to the mid and upper 70s across the northern half of the Sacramento Valley.

Approaching weak trough will begin to assert its influence on the region’s weather today. The marine layer is expected to continue deepening setting up and increasingly strong onshore surface pressure gradient as temperatures will remain hot well inland (northern Sacramento Valley and over the mountains). Gusty onshore winds will develop by later this afternoon and will continue through this evening.

Trough moves overhead Wednesday, and with a deep marine layer, may see some stratus make it inland into the southern Sacramento Valley. Highs are expected to be around 5-10 degrees cooler than today’s with the biggest drop where the Delta Breeze has its strongest influence (Sacramento and Stockton areas). Best chance of thunderstorms on Wednesday will be north of the forecast area, but far northwest Shasta County may see an isolated late day storm.

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Trough lingers over the region Thursday and Friday, but heights aloft will be gradually rising. Onshore flow will be slackening allowing a gradual return of warmer temperatures.

Wildfire smoke possible at times across the region the next few days, especially north of Sacramento. Onshore flow expected to bring considerably higher humidity the next few days.

Extended Discussion (Saturday through Tuesday)

Ensembles continue to depict broad troughing breaking down for the weekend, which means we will see an increase in high temperatures. Temperatures will rise back above normal for the weekend and early next week with Valley highs in the mid 90s to 105 and 70s to 90s in the mountains and foothills.

Although onshore flow will be weaker than midweek, a moderate Delta Breeze will remain in the nights which will keep morning lows mild around the southern Sacramento Valley and portions of the northern San Joaquin Valley.