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October 2, 2020 – Well above normal temperatures and very dry conditions continue into Saturday with areas of wildfire smoke affecting portions of interior NorCal. Continued dry weather with a slight cooling trend Sunday and into next week, although daytime high temperatures will remain several degrees above normal.

Discussion

Blocking ridge along the W coast of NOAM will continue today, then will begin to weaken this weekend. A hot, dry air mass will continue over NorCal with light winds and smoky conditions into the start of the weekend.

Shifting of the high pressure cell to the west today and over the SoCal area on Sat will lessen the impact of northerly winds. Lighter winds will likely mean the smoke will linger over much of the CWA through Sat. Due to lingering smoke, have kept the max temps a few-several degrees below the guidance over much of the CWA today, and also on Sat due to smoke and in addition to the weakening ridge. Still max temps will continue well above normal, mostly some 9 to 19 degrees above normal today, and mostly 7 to 18 degrees above normal on Sat. In addition, humidity recovery will remain poor to moderate over the higher terrain through the weekend due to a strong subsidence inversion.

On Sun and Mon, onshore floor will provide some much needed relief with max temps “cooling” into the 80s to low to mid 90s in the Valley and mostly 60s and 70s in the high Sierra. Still, this is up to 8-10 degrees above normal in the lower elevations and about 8 to 14 degrees above normal in the mountains. Repositioning of the high pressure cell over the Desert SW and a flattening of the ridge over the Pac NW due to the passage of a weak trof will allow for modest cooling in NorCal. Perhaps a little weakening on the W side of the ridge from the weak low currently near 30N/135W moving closer to the SOCAL coast as well.

Today is day 2 of the new water year; and still no rain as Hurricane Marie moves westward beneath the blocking high. But wait; a pattern change late next week?

Extended Discussion (Tuesday through Friday)

GEFS and EC ensemble in general agreement weakening the persistent West Coast ridge and shifting it east by Thursday. Pattern remains dry for NorCal with temperatures still around 10 degrees above average early in the week, returning to only slightly above average by Thursday.

Bigger changes in the offing for late in the week with ensembles indicate approaching trough potentially tapping remnant moisture from Hurricane Marie. Both GEFS and EC ensemble develop precip across NorCal by next weekend. Stay tuned.