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September 10, 2020 – Smoke and haze from wildfires will continue to impact air quality and temperatures.

Discussion

Smoke will continue to cause problems with the daily high forecast the next few days but in general cooler temperatures below seasonal normals will likely continue today. Have some warming for Friday and Saturday thinking the hazy and smokey conditions will not be as thick those days and will allow the interior to warm a little better. This is mainly due to the wind pattern that will set up with winds aloft mainly from a southerly direction. The unknown at this time is how much smoke from the wildfires south of the area will bring northward and its location. The Creek wildfire will likely bring smoke northward at some point at least for portions of the foothills and mountains with a chance it could get into the valley this far north. Overnight lows will stay cooler into the weekend with lows expected to cool to near seasonal normals each night.

A trough of low pressure will approach the area Saturday and Sunday. Current thinking is that we should see less smoke and haze over the weekend for most areas with some cooling on Sunday over Saturdays high temperatures along with increased flow through the Delta.

Extended Discussion (Monday through Thursday)

Forecast remains on track as guidance continues to show an trough approaching the West Coast on Monday. Timing, strength, and placement are still a bit iffy, but the overall pattern change appears likely. Onshore flow associated with this trough will usher in some moisture to the region. Latest guidance has showers possible over the southern Cascades and the far northern Sierra, generally north of highway 36. However, in addition to possible precip chances, there will also be an increase in southwest winds which may lead to possible fire weather concerns from Sunday afternoon through Wednesday. The strongest winds should be over the the upper foothills and mountains, where gusts from 30 to 40 mph will be possible. Brief gusty periods may also occur over the Valley mainly during the late afternoons.