June 4, 2019 – Afternoon and evening mountain showers and thunderstorms today mainly south of Interstate 80. For the Valley, much above normal temperatures through Wednesday then cooling into the weekend.
Discussion
Strong upper level ridge will bring much above normal high temperatures this afternoon and again Wednesday over much of NorCal. Readings will reach into the mid and upper 90`s, which is 10 to 15 degrees above normal for early June. This will lead to moderate heat risk for sensitive groups during peak heating hours of the afternoon. Overnight low temperatures cooling back into the 60’s Tuesday night and Wednesday night will provide some relief and keep the area below heat advisory levels.
Thunderstorm coverage is expected to shift south this afternoon compared to the past few days with best chances mainly south of Interstate 80. WRF mesoscale models are highlighting higher elevations of Tuolumne county from Strawberry to Hetch Hetchy as the main focus for strong thunderstorms this afternoon. Increasing westerly flow with trough dropping south along the west coast will push instability and thunderstorm chances east of the area Wednesday and beyond with dry conditions returning.
Extended Discussion (Saturday through Tuesday)
Upper level trough centered over the Pacific Northwest extends into far northern California Saturday. Continue to lean on the NBM with generally dry weather expected.
Northerly winds will increase in the Sacramento Valley Saturday and Saturday night as high pressure ridging builds to the north and the surface pressure gradient increases. This will bring lowering humidity and will begin to dry out grasses and other fine fuels.
Another warm up will be seen late in the weekend into early next week as upper level ridging builds in. Expected Valley highs to return to the 90`s Sunday and beyond.