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September 2, 2020 – Smoke and haze from wildfires will continue to impact air quality and temperatures this week. Dry weather and above average temperatures expected through Friday. Record heat possible Labor Day weekend into early next week.

Discussion

Clear skies cover the region early this morning with localized lingering smoke and haze from the wildfires. The north and east surface pressure gradient has decreased considerably from yesterday, and winds are lighter. Profiler data indicate the marine layer has deepened above 2k ft and onshore flow has picked up through the Delta. RH’s are up across most of the lower elevations, but areas of low RH (20-35%) remain across the foothill and mountain thermal belts. IR difference imagery shows coastal stratus extending further inland compared to 24 hours ago, and a few bits of stratus may make it inland into the Sacramento area around sunrise.

High pressure settling over the region will continue to bring a warming trend for the remainder of the week into the weekend. With the exception of the Delta Breeze, lighter winds are anticipated this week which may allow for more smoke to build over the Valley by late week as a stronger subsidence inversion develops around 850-700 mb. Any local dense smoke will impact high temperatures.

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The Delta Breeze and increased onshore flow will spread significant cooling inland along with higher humidity today. Temperatures will inch up a few degrees each day beginning Thursday, and humidity will begin to lower. More widespread, possibly dangerous, heat arrives this weekend.

Extended Discussion (Sunday through Wednesday)

The hottest temperatures of the week are expected Labor Day weekend into early next week as strong anomalous ridging resides over NorCal. Peak heating may occur on Sunday and Monday, with the potential for 100 to 110 readings in the Valley, foothills and portions of the Delta. Little to no overnight relief is expected as low temperatures remain in the upper 60s to around 80 degrees. Thus, an Excessive Heat Watch is in place through Tuesday afternoon. Please learn the symptoms of excessive heat exposure, stay hydrated and never leave children or pets unattended in vehicles. Highs may be affected by smoke amounts which tend to keep conditions cooler. Dry weather is anticipated to continue. Latest ECMWF and CMC ensembles depict a stronger slider coming through the Great Basin Monday night into Tuesday. If this verifies, there is the potential for north to east winds as well as less heat than currently advertised.