October 20, 2018 – Dry into next Wednesday, then a slight chance of light precipitation mainly over the Coastal and Shasta mountains late Wednesday into Friday. Above normal temperatures trending down to near normal by middle of next week.
Discussion
Blocking pattern established along the West Coast with NorCal sandwiched between upper high to the north and trapped closed low to the south. EPAC surface high extends through PacNW into Great Basin. With lower pressure over Interior NorCal, some gusty easterly wind is occurring through the eastern foothills and mountains. Strongest winds are occurring over Sierra Nevada ridges and through favorably oriented canyons. Gradient weakens by this afternoon as high pressure shifts east and closed trapped low retrogrades offshore.
High temperatures today are expected to be within a few degrees of Friday’s numbers. Closed low shifts back over CA Sunday and lingers into Monday, weakening to trough and shifting east Monday night. Short wave ridging follows Tuesday with diffluent flow aloft which helps to weaken approaching baroclinic zone.
Dry weather continues through Tuesday with high temperatures trending down to near normal by the middle of next week.
Extended Discussion (Wednesday through Saturday)
Weak frontal system forecast to move through the Pacific Northwest on Wednesday has trended north in latest models runs so have kept Wednesday forecast dry. Daytime temperatures will take a small dip through dropping down to right about normal for for this time of year.
Next, slightly stronger system forecast to push into the Pacific Northwest and NorCal Wednesday night. This system may also shift northward in future model runs but for now, will keep slight chance wording in the northern coast range and northern mountains for Wednesday night and Thursday with a few lingering showers possible in this region going into Friday. Thursday will see temperatures remaining right around normal with the start of a warming trend Friday as a ridge of high pressure starts to amplify along the west coast. Warming and drying continues on Saturday with good model consensus in continued ridge building along the west coast.