Dry and warm through Thursday, possibility of precip this weekend

November 2, 2020 – Dry weather with above average high temperatures persist through Thursday. Cooler this weekend with a threat of showers, mainly over the foothills and mountains.

Discussion

Other than some high clouds drifting into the southern portion of the forecast area (associated with the weak closed low to our south), skies are clear across the region early this morning. A moderate east surface pressure gradient remains in place (RNO-SAC currently around 6 mbs) resulting in some local breeziness across the foothills and northern Sierra (similar to yesterday morning) and helping to maintain low RH’s outside of valley and drainage bottoms.

High pressure will remain in place through much of the upcoming week continuing the dry and mild weather pattern. An incoming short-wave on Tuesday will bring an increase in high clouds to the area, and may initiate a return of weak onshore flow resulting in a few degrees of cooling and slightly higher RH.

High pressure rebounds Wednesday ahead of the strong upstream trough digging southeastward through the Gulf of Alaska. Warm and dry weather expected to hold across NorCal through Thursday as the trough approaches, then a few showers are expected to develop Thursday night across the northern third of the forecast area as it swings onshore across northwest California.

Extended discussion (Friday through Monday)

Pattern change is in store by the end of the week as an upper level trough digs south along the West Coast on Friday and Saturday. There remain some model differences with the exact placement/timing. Will note the 00Z ECMWF and GFS are starting to arrive at a better consensus for precipitation amounts, particularly when compared to model runs from the past several days. Overall, very light rain amounts are forecast for the Sacramento Valley with little/none south of Chico. For the Sierra, wouldn’t be surprised if at least a few to several inches of snow materialize, if the current forecast holds. While there remains low confidence on precipitation amounts, there is much better confidence that this trough will usher in a much colder airmass, quickly flipping us from above normal to below normal. Additionally, breezy conditions will be possible, especially as this trough passes with the development of northerly winds late weekend or early next week.