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October 5, 2020 – Dry weather with unseasonably hot temperatures continues early this 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

Clear skies cover the region early this morning as strong ridging continues to extend from the Desert Southwest into NorCal. Surface pressure gradients remain similar to 24 hours ago and winds are generally light except for local breeziness across some foothill locales. The airmass remains very dry with RH’s currently in the teens to 30s percent outside of valley and drainage bottoms.

Not a whole lot of change expected today and Tuesday as high pressure persists. The marine layer will remain shallow with limited influence inland. Temperatures will remain around 10-15 degrees above average despite continuing wildfire smoke that will influence air quality and daytime heating.

Weak low forecast to lift north into central California on Wednesday bringing some mid and high cloudiness, and helping to initiate cooling inland as stronger onshore flow develops and the marine layer deepens.

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.

Extended Discussion (Friday through Monday)

Models continue to offer differing solutions from run to run in the extended forecast. Latest guidance showing closed upper low approaching the CA coast Friday, shifting inland Friday night.

Low forecast to track across the central part of CA where bulk of precip is expected.

Pacific frontal system spreads more precipitation over interior NorCal from the NW Saturday. Model QPFs differ with the EC a significantly wetter solution compared to the GFS-FV3 which would be beneficial to ongoing wild fires.

Drier weather expected Sunday into Monday, with some breezy north to east wind, as EPAC high pressure builds inland.