Seasonably warm weather early this week. Hot conditions with high to very high heat risk expected for the second half of the week. Excessive Heat Watch from Thursday afternoon through Saturday evening.
Persistent upper trough that has remained off the West Coast all weekend remains nearly stationary with a front and associated showers remaining over northwest California. Skies are mostly clear except for some areas of clouds over the northern mountains. Southerly breezes are beginning to pick up again across the northern half of the Sacramento Valley as slight pressure falls occur to the northwest and north of the region. Southerly gusts in the teens to around 30 mph north of Willows and Oroville.
Another short-wave will lift northeast across far northern California later today bringing a renewed chance of showers across Shasta County, but precipitation amounts will be very light (generally under a tenth of an inch). Breezy conditions will become more widespread by afternoon as surface pressure gradients tighten. Highs today will be in the 80s across the Central Valley, around 5-10 degrees cooler compared to Sunday.
Warming returns Tuesday as the trough finally lifts out to the northeast as high pressure centered over the Southwest expands westward. Highs will return to the lower 90s across most of the lower elevations and surface winds will transition from onshore to light northerly.
Heat cranks up Wednesday with highs expected to exceed triple digits across the Central Valley, then record breaking heat forecast to begin Thursday as most valley highs will range from 105-110 degrees. Overnight lows will also be very mild, ranging from the upper 60s to around 80 across most of the valley, and foothill and mountain thermal belts.
Extended discussion (Friday through Monday)
High pressure over the Desert SW will continue near record to record heat over interior Northern California Friday. Ridge gradually weakens through the weekend into early next week. This will result in a slow downward trend in high temperatures with 90s returning to Delta breeze influenced areas Sunday. Highs in the 90s become more widespread in the Central Valley Monday with triple digit heat lingering in portions of the Northern Sacramento Valley.