Cooling trend spread inland today and persists through the weekend. Chance of rain across much of the region over the weekend. Isolated thunderstorms may lead to dangerous lightning activity and gusty winds, impacting outdoor activities. Widespread triple digit temperatures with moderate Heat Risk late next week.
Discussion
Partly to mostly cloudy skies cover interior NorCal early this morning as Gulf of Alaska low edges closer to the West Coast. Onshore flow continues to spread cooling inland, and current temperatures are mostly running around 3 to 7 degrees cooler (and RH is up 15-25 percent) compared to 24 hours ago. Current temperatures range from the upper 50s to lower 70s across the Central Valley.
Cooling will spread inland today as breezy onshore flow picks up. Inland areas will see around 5-10 degrees of cooling compared to Thursday’s highs. The next chance of showers will occur tonight and Saturday across the northern half of the forecast area as deeper moisture moves in from the southwest and weak forcing spreads over the area. QPF will be light and mainly confined to areas well to the north of I-80.
By Saturday night into Sunday, a deeper plume of moisture will reach NorCal (drawn northward ahead of the retreating Gulf of Alaska low), and a little stronger forcing is expected to generate widespread light precipitation over much of the region. QPF could range from 1/2 to 1 inch in the northern Sierra and northern mountains, and even the valley may see some rain (especially the northern Sacramento Valley where 1/3 to 1/2 inch may occur).
Precipitation turns more convective Sunday afternoon as the moisture plume sags south, and a few thunderstorms may be possible. The low continues retrograding early next week and ridging is forecast to rebuild over NorCal leading to warmer and drier conditions.
Extended Discussion (Tuesday through Friday)
Upper ridge moves through interior NorCal Tuesday then gradually amplifies over the Intermountain West through the remainder of the week. This will result in some locally gusty wind at times and a warming trend.
High temperatures climb from about 10 degrees above normal Tuesday to upwards of 20 degrees above normal by the end of the week. Triple digit heat expected in the Central Valley Thursday and Friday.