Cool and dry weather will continue through much of the weekend. A pattern change will bring increasing rain chances Monday into Tuesday. Gusty southerly winds expected Sunday and Monday. Dry weather returns by Tuesday afternoon, with mild temperatures remaining through the end of next week.
Latest GOES-West Nighttime Microphysics satellite imagery depicts some high clouds passing by to the north and the south, as well as some marine stratus developing just west of the Delta. Current weather conditions across interior northern California consist of mostly clear skies with generally light winds and temperatures in the 50s to 60s across the Valley and foothills, with mid 30s to 50s in the mountains, valid at 0230 PDT.
Upper level troughing will allow for cool temperatures and locally breezy onshore winds to continue today. Temperatures are forecast to reach generally 5 to 10 degrees below normal for mid to late September climatology this weekend. Mid 70s to low 80s are forecast for much of the Valley, with 70s for the foothills, and 50s to 70s for the mountains. Overall tranquil weather will prevail across the region today.
Later this weekend into early next week, we turn our attention to a pattern change. As an upper level low drops down from the Gulf of Alaska, we see increased pressure gradients.
On Sunday, increased southerly winds are forecast across much of the area, with current sustained winds of 10 to 15 mph with gusts up to 25 to 30 mph expected. Even stronger southerly winds are forecast for Monday, sustained 15 to 25 mph with gusts 25 to 35 mph.
Strongest winds are expected in the northern Sacramento Valley, southern Cascades, and Sierra Nevada. The National Blend of Models (NBM) advertises a 25 to 55 percent probability of gusts reaching 40 mph on Monday over the northern portion of our forecast area.
Rain chances will also return to portions of interior NorCal with this pattern change. The majority of the precipitation favors far northwestern California, however current guidance suggests storm total precipitation amounts of 0.50 to 1.75 inches across Shasta County and the Coastal Range, with much lighter amounts potentially down south to the Sacramento Metropolitan Area (couple hundredths of an inch).
The NBM probabilistic data shows generally a 60 to 85 percent probability of a half of an inch of rain over 48 hours ending Tuesday over Shasta County and the Coastal Range. From Red Bluff to Interstate-80, NBM guidance suggests probabilities of 20 to 35 percent for the same threshold and timeframe.
Wind and rain will be the main impacts in the short term. Temperatures will also be on the cooler side, for both the daytime and overnight temperatures as well. People should consider securing any loose outdoor objects such as trash cans or decorations, and plan ahead for a wet and windy Monday commute, especially for those living in the northern/central Sacramento Valley and surrounding terrain!
Extended Discussion (Wednesday through Saturday)
Ensemble guidance and cluster analysis generally suggest that there is some uncertainty with the progression of this upper level trough over the extended forecast period, however seasonably cool temperatures are expected to continue next week.
Daytime high temperatures are forecast to remain in the 70s and 80s for much of the Valley and foothills. For the mountains, high temperatures in the upper 50s to mid 70s are forecast. Periods of locally gusty winds are also expected next week.
Additionally, depending on the progression of the trough, we could see a more northerly component to the wind late in the week into next weekend, and/or additional shower chances.