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May 15, 2018 – Afternoon and evening thunderstorms possible over higher terrain for much of this week with a chance of showers across the region Wednesday.
Other than some clouds across the mountains, and stratus developing from the Delta into the Sacramento area, skies are clear across the region early this morning. Steady onshore flow continues with a deep marine layer (over 3K feet). Current temperatures range from the upper 30s to lower 40s in the mountain valleys to the 50s to around 60 elsewhere.
Satellite imagery shows the closed low continuing to spin across northern Nevada while another approaches from the west (currently crossing 130W north of 30N). Another day of mainly afternoon and evening mountain showers and thunderstorms is expected as the Nevada low is kicked northward by the approaching low offshore.
More widespread shower and thunderstorm activity is expected on Wednesday, including the Central Valley, as the offshore low moves inland across the Bay Area and then into the Central Valley in the vicinity of Sacramento and Stockton. The system is forecast to shift eastward Thursday and Friday returning shower chances to mainly the mountains.
Temperatures will continue to cool today and Wednesday in response to the onshore flow and synoptic cooling, but are expected to return to around average later this week.
Extended discussion (Saturday through Tuesday)
Models showing upper low developing off the West Coast late Saturday into Sunday. Low then forecast to deepen and dig along the CA coast into Monday, eventually tracking inland over SoCal late Monday into Tuesday. This will keep a threat of showers and afternoon thunderstorms over mainly the mountains. High temperatures forecast to remain a little above normal through the extended period with mainly 80s in the Central Valley, and 60s to 70s for the mountains and foothills.