Shower/thunderstorm chances over the mountains today, then become more extensive beginning Monday. Temperatures will be above average today, then cooler weather returns.

Chance of thunderstorms  and showers today

Discussion

Skies are mostly clear across interior NorCal early this morning. Debris cloudiness from Saturday’s convection in the Sierra is moving north along the Nevada border. High pressure over the region is resulting in milder temperatures, and is suppressing marine influence inland. Current temperatures are milder than 24 hours ago and generally range from the 50s to mid 60s in the mountains, to the 60s to mid 70s across the Central Valley.

Heat safety tips

Hot weather will continue today with most areas likely to see the warmest temperatures of the week, and some areas of the northern Sacramento Valley may reach the century mark. Widespread moderate heat risk will cover the valley and lower foothills. Isolated to scattered late-day thunderstorms will spread further north up the Sierra and Cascade Range today.

Moisture will continue to flow into NorCal from the south and east through mid-week as a low develops near the central California coast. This will lead to an increasing threat of mainly late day showers and thunderstorms over the mountains as TPW and elevated instability increase, and some of these storms may migrate down into the valley in the evenings.

Thunderstorms and showers throughout the week

Heavy rain will be possible with thunderstorms, and increasing bulk shear of 20-30 kts on Monday and Tuesday may lead to a non-zero threat for large hail with stronger storms.

The combination of increased cloud cover, synoptic cooling from weakening high pressure, and increased onshore flow will result in a cooling trend for the entire area by Tuesday with high temperatures returning to below normal.

Area waterways continue to run cold and fast as a consequence of the melting Sierra snowpack. Be sure to exercise cold water safety if you’re near area waterways this weekend.

Extended Discussion (Thursday through Sunday)

Closed upper low weakens to trough Thursday as it moves into the Great Basin. Another short wave trough looks to follow it Friday into the weekend.

Threat of afternoon and evening showers and thunderstorms will continue over the mountains and possibly into the northern and central Sacramento Valley. NBM forecasts near to slightly below normal high temperatures Thursday into Saturday, warming to slightly above normal Sunday.