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Cooling trend through Wednesday with below normal temperatures. A few showers or thunderstorms will be possible over the northern mountains today and Wednesday, otherwise dry weather continues.

Discussion

Satellite imagery shows the large trough over the eastern Pacific continuing to deepen offshore NorCal. Mid/upper level front remains draped across the region with strong southwesterly flow evident on water vapor imagery.

Moderate to strong onshore surface pressure gradient covers the region and breezy southerly wind gusts in the teens to around 30 mph extend from the Delta northward up most of the Sacramento Valley. Current temperatures are running around 5-10 degrees cooler across most of the area compared to 24 hours ago.

The large trough won’t move much today, so breezy to windy conditions will persist, but likely not quite as strong as Monday as the thermal gradient begins to ease. Limited moisture remains pooled across the far northern portion of the state, and its possible a few late day showers will develop over the mountains of northwest Shasta County. Highs today will be down another 5-10 degrees compared to Monday’s and will only be in the 70s across the Central Valley.

Upper trough moves in Wednesday with scattered showers and a few thunderstorms possible across the north end of the Sacramento Valley and surrounding terrain with only modest instability expected. Temperatures will be similar to today’s, and renewed breeziness will be possible in the afternoon and evening.

Short-wave ridging moves overhead Thursday, then the next upstream trough will be approaching for the weekend. Temperatures will be warming slightly.

Extended discussion (Saturday through Tuesday)

Cluster analysis continues to show an upper low off the coast this weekend. A shortwave with a surface cold front is projected to brush through northwestern California. With the low trending further west, weekend weather over interior NorCal is trending drier with the potential for rain showers just barely edging it into far western Shasta County on Saturday. Most of the area will remain dry. This continues the model ensemble trend we have been seeing in recent days, removing the potential for significant precipitation.

With the low more off the coast, heights are forecast to slowly build over Northern California this weekend, leading to temperatures warming back to above normal levels. Valley highs are forecast to reach the low 90s for the weekend into early next week. Another shortwave brushes by early next week, but ensembles show dry weather except for far northwestern California, generally outside of the forecast area.