May 25, 2018 – Widespread showers and isolated thunderstorms today across the area. Afternoon and evening thunderstorms possible mainly over higher terrain into next week. Cooler than normal temperatures continue across most of the region through Saturday, warming to well above normal for early next week.
Rain showers and thunderstorms are spreading into the area this morning. These are expected to become more widespread through the morning. Heaviest precipitation south of I80 is expected in the morning, north of I80 in the afternoon and early evening. Brief heavy downpours and some small hail can be expected in the stronger storms. Commuters should be prepared for slick conditions and ponding of water on roads, and should leave extra time for travel.
Snow levels are quite high currently, over 9000 feet, but will drop to around 8000 feet later in the evening. A Winter Weather Advisory continues into Saturday morning for areas of the Sierra above 8000 feet and south of Highway 50, where up to 5 inches of snow is possible. High elevation hikers and campers this weekend should be prepared for wintry conditions.
Today will be the coolest day of the week as the upper low passes directly overhead. Temperatures across the area will range between 10 and 20 degrees below normal. The record low maximum for downtown Sacramento for the date is 65, set in 1915. Our forecast high is 66, so it will be close to record cool.
Saturday morning showers are possible over the mountains and the Valley north of I80. Drier conditions are expected for the Valley by afternoon, with showers and thunderstorms over the foothills and Sierra- Cascade range. Valley temperatures will be warmer, in the mid 70s to near 80, with some afternoon clearing.
Heading into Sunday and upper level ridging builds and temperatures will begin to warm back to above normal levels. For Memorial Day, dry and very summer-like weather is expected,with Valley and Delta highs in the 90s.
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Extended discussion (Tuesday through Friday)
Upper troughing pushing into the eastern Pacific will bring a slight cooling to the otherwise well above normal daytime temperatures. Models also hint at a shortwave disturbance pivoting out of this trough bringing a slight threat of showers over the northern Sierra or Shasta county mountains depending on model. Forecast models push the main trough into NorCal next Wednesday bringing an increased chance of showers or thunderstorms over the Sierra Cascade range. More significant will be a substantial drop in daytime temperatures with highs expected to come in just a bit above normal. Upper troughing over the west coast will still play a role in NorCal weather next Thursday but model differences make it difficult to place any thunderstorm threat. Have kept showers over the Northern Sierra for this forecast cycle. Most locations should see a continued drop in temperatures however with highs coming in right around normal. Upper trough should shift east of the forecast area by the end of next week but upper troughing over the Pacific northwest should keep temperatures from heating up much.