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October 6, 2020 – Dry weather with unseasonably hot temperatures continues into mid-week, then much cooler with a chance of precipitation by the end of the week. Wildfire smoke will continue to influence air quality and temperatures.

Discussion

Skies remain clear early this morning as high pressure covers the region. The airmass over NorCal remains very dry with current RH’s in the teens to 30s percent outside of valley and drainage bottoms, similar to the past several mornings. Enough north to east surface pressure gradient remains for local breeziness across some foothill locales, and coastal influence remains very limited as profiler data indicate the marine layer remains shallow (at or below 1k ft in depth).

Nearly persistence forecast today as wildfire smoke forecast to continue to thin. Highs today will once again be around 10-15 degrees above average.

Weak mid/upper low still forecast to lift northward into central California Wednesday. Some mid and high clouds will begin to spread into the southern portion of the forecast area tonight. The system will also help to initiate cooling inland as stronger onshore flow and a deeper marine layer finally return.

Cooling expected to accelerate Thursday as cloud cover increases ahead of approaching upper trough. Temperatures will cool to a little below average, and humidity will increase substantially.

Still lots of uncertainly on timing the onset and extent of precipitation with the initial system Thursday night and Friday.

Operational runs continue to oscillate wildly, especially the GFS, so will continue to lean toward the ensemble EC and NBM with some light precipitation across the region on Friday.

Extended Discussion (Saturday through Tuesday)

Pacific frontal system moves across interior NorCal Saturday with models differing on southern extent of associated precipitation.

EC has been more consistent run to run, and forecast leans towards that solution. Thus expect wetting precipitation for most of the CWA Saturday into Saturday night.

Drier weather with some locally gusty north to east wind suggested by progs Sunday into Tuesday as EPAC high builds inland.