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May 16, 2019 – Showers and isolated thunderstorms today with snow and travel issues over the Sierra passes. Gusty south winds in the Sacramento valley. Mountain showers mainly ending on Friday. Rain and mountain snow returns Saturday afternoon. Showers Sunday with shower threat continuing through middle of next week.
Back edge of cold frontal band now working its way eastward through the Sacramento and northern San Joaquin valley with a shield of precipitation across the eastern half of the CWA. Surface observations and Radar indicate snow levels at around 7000 feet at this time so summits likely being impacted. Breezy south winds in the Sacramento valley have dropped off some now that the front has passed eastward but expecting an increase in wind this afternoon as the upper low associated with the front moves inland. Showers will be a pretty good bet most areas of the CWA today as the upper low slides across the north state. Enough instability is indicated for a slight threat of thunderstorms over the region as well. Colder air moving into the region will bring down snow levels today with snow levels down to about 5000 feet by mid morning. Daytime highs today will drop as well down to as much as 20 degrees below normal for the date.
The main upper low is forecast to shift into the Great Basin over night so most areas should see decreasing showers. By Friday afternoon the shower threat will linger over the Sierra crest and northern mountains but the remainder of the CWA should see clearing. Most areas should see an uptick in daytime temperatures as a shortwave high pressure ridge slides over the west coast. Friday night looks dry under this ridge most areas but GFS and NAM both want to throw a shortwave across the northwest corner of the state for a sLight threat of showers northern Shasta county.
Next Pacific frontal system pushes inland on Saturday for another round of precipitation over forecast area. This frontal system should move east of the forecast area by Sunday morning with Sunday seeing mainly shower activity through the day. This system currently appears weaker than the system currently moving through the region but with snow levels expected to be below pass levels, travel impacts are again likely.
Extended Discussion (Monday through Thursday)
Unsettled weather, below average temperatures, and breezy winds continue through next week. A closed low moving across California towards the southwest US Monday may briefly allow for dry conditions in the Valley before ensemble means depict another trough axis moving across NorCal Tuesday night. Chances for showers continue across the Sierra and northern mountains early next week with snow levels Monday near 6000 feet.
Snow levels will be on the rise Tuesday and through the rest of the week as the next system moves into the area by mid-week. Temperatures slowly increase just below normal values by Thursday, with Valley highs in the upper 70s by Thursday afternoon. Chances for showers continue across all of NorCal through the end of the week.