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October 2, 2019 – Gradually milder temperatures are expected through the remainder of the week with highs returning to around average by the end of the week.

Discussion

Short-wave ridge resulting in clear skies across interior NorCal early this morning. Current temperatures range from the 20s in the mountain valleys to the 40s to lower 50s across the Central Valley. It’ll be another chilly start today.

Temperatures will warm a bit more today as the ridge transits the area. The next upstream trough will move through NorCal on Thursday leading to slight cooling, but shower chances are expected to remain to the north and east of the forecast area.

Ridging finally builds in the wake of the trough at the end of the week and this weekend allowing temperatures to finally return to close to average for early October.

Extended Discussion (Sunday through Wednesday)

To conclude the weekend, amplified/progressive flow will continue across the mid-latitudes with broad ridging extending over the West Coast. A subtropical upper low lifting northeastward toward the state could produce some high clouds on Sunday. However, the system will be in the process of shearing out thus limiting sensible weather impacts. Valley high temperatures are expected to reach the mid to upper 80s which is 3 to 6 degrees above climatology.

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Moving to next week, the mean upper ridge will have advanced to the Intermountain West by Monday with a full-latitude trough sitting over the eastern Pacific. Deterministic models continue to waver with the offshore pattern, particularly due to the complexity of merging a pair of systems.

It appears the northern most cyclone centered over the Gulf of Alaska will dominate with the southern extension of the trough possibly grazing northern California. Temporal differences continue between the 00Z GEFS and 00Z ECMWF ensemble means with the former being 12 to 24 hours quicker.

At this juncture, some increase in clouds is likely from warm advection ahead of the trough. This will cool temperatures off a bit, generally down to the low 80s for next Tuesday and Wednesday (Oct 8/9). Confidence is low in precipitation chances but it will be worth keeping an eye on.