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October 3, 2017 – Cooler weather with breezy north winds early this week. Lighter winds late in the week with warming temperatures. Slight chance for showers along the northern Sierra crest into this evening.
Clear skies across much of interior NorCal, but clouds have increased over the far northern portion of the state overnight as the upper low closes off. Current temps are considerably colder across most of the area range from the 20s in the mountain valleys to the mid 40s and lower 50s through much of the Central Valley.
Much of the area is seeing lighter winds compared to 24 hours ago, but gusty north winds continue across the northern Sacramento Valley and temperatures there remain in the mid 60s.
Northerly surface gradients remain tight (around 12 mbs MFR-SAC currently), but surface winds are light through much of the valley as the boundary layer has decoupled, upper support is much lighter and subsidence weaker as the low approaches. Most of the breeziness today will be confined to the northern half of the Sacramento Valley and surrounding terrain.
Confidence continues to increase for the potential for showers across the northern Sierra this afternoon and evening as the low drops southward. An inch or so of quick snow accumulation may occur over the mountain passes near Tahoe.
The low moves east tonight and Wednesday with dry and milder weather through the remainder of the week.
Extended discussion (Saturday through Tuesday)
Dry weather for the weekend into early next week as area is sandwiched between ridging off the West Coast and troughing digging into the Great Basin. Northerly flow will increase again by the end of the weekend as a result. Latest guidance is coming in breezier than previously forecast so have bumped up winds for Sunday into next week, though not as high as the current GFS would suggest. Will need to watch as we may see another period of near critical fire weather conditions given warm temperatures, breezy north winds, and low humidity. Temperatures will be warm on Saturday, some 4 to 7 degrees above normal, with valley temperatures in the mid to upper 80s and mountains in the 60s to 70s. Slight cooling expected for Sunday and Monday, with temperatures back down to near normal by Tuesday.