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September 11, 2020 – Smoke and haze from wildfires will continue to impact air quality and temperatures. Weak weather system will bring onshore flow and periods of gusty winds Sunday through early next week.

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 through the weekend with today being the coolest. Have minimal warming for today over yesterdays highs as 850 mb temperatures warm slightly. Current thinking is that the thick smoke will be around through Saturday with some improvement Sunday and better improvement on Monday. Saturday 850 mb temperatures warm slightly over Friday so have slight warming in the forecast for Saturday. Any improvement in the thickness of smoke is expected to be slight.

A trough of low pressure will approach the area late Saturday and Sunday shifting the high pressure over the region to the east. Current thinking is that we should see less smoke and haze starting Sunday but enough lingering around to still have some impact on daily high temperatures. Stronger onshore flow through the Delta is expected as well that will help to keep the Sacramento region a little cooler than normal.

On Monday the through moves close enough that southerly winds aloft will shift southwest. This should help to carry any additional smoke aloft from wildfires in the Sierra Nevada moving northeast away from the valley. Some drainage of surface smoke may still occur Sunday night and Monday morning towards the valley. Temperatures will be similar to Sundays highs on Monday with maybe slight warming for the Sacramento region southward.

Extended Discussion (Tuesday through Friday)

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The pattern shift remains on track for early next week as an upper level trough approaches the West Coast. This will bring increased onshore flow to the region, leading to cooler temperatures, increasing moisture, and increased winds at times. Flow will be from the south to southwest throughout much of the period, which may lead to periods of elevated and locally critical fire weather conditions, particularly in the foothills and mountains.

As previously mentioned, there will be an increase in moisture with this pattern change which should provide moderate overnight humidity recoveries. In addition to those, there could be some isolated showers and thunderstorms across the northern portion of the Sacramento Valley and nearby mountains. Guidance still struggles with the timing, place, and potency of this opportunity, so this will have to be something we continue to watch.

Confidence continues to remain low with precip chances, but high with the change in the weather pattern to cooler weather and breezy winds.