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October 17, 2019 – Light showers northern mountains and northern Sacramento valley this morning as a weak frontal band moves through with another round of light showers northern mountains on Saturday. Otherwise dry through the extended period. Below normal daytime temperatures through the weekend then above normal temperatures next week as high pressure moves across the region.

Discussion

Weak frontal band currently moving through NorCal bringing light showers to the northern Sacramento valley and surrounding mountains. So far, precipitation amounts of been on the order of a few hundredths of an inch. Associated weak upper trough is forecast to move into the western Great Basin by this afternoon as high pressure begins building over the west coast. May see a slight threat of showers over the northern Sierra this afternoon as NorCal transitions from cyclonic to anticyclonic flow. Cool air filtering in behind the front will bring a significant cool off today with daytime highs forecast to drop to several degrees below normal for this time of year. Flat high pressure over the west coast on Friday will keep conditions dry but high clouds are likely to slide over the region. Only a slight warming is expected most areas.

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Models in good agreement in bringing another weak disturbance through the Pacific Northwest and NorCal on Saturday. This will bring a threat of light showers to the northern mountains during the day. More cooling is expected with daytime highs over the northern Sacramento valley dropping to 10 or more degrees below normal. This weak disturbance moves quickly east of the region with the precipitation chances ending by Saturday evening. High pressure starts rebuilding on Sunday bringing a little warming but daytime highs are still expected to remain below normal.

Extended Discussion (Monday through Thursday)

Ensemble solutions remain in fair agreement that a building high pressure will result in warmer conditions next week. Daytime highs are expected to be 5 to 10 degrees above seasonal normals, with widespread low to mid 80s in the Valley. The strengthening ridge of high pressure will keep stable conditions over interior NorCal. Models indicate that locally breezy northerly to easterly winds could be possible around the middle of next week as pressure gradient tightens.