June 1, 2019 – Afternoon and evening mountain thunderstorms through the weekend. Decreased showers early next week. High snow levels. No shower activity across interior NorCal during the second half of the week. Warmer than normal temperatures through the extended period.
A few scattered clouds over the Sierra Cascade range this morning but otherwise skies have once again cleared out under more stable night time conditions. The upper low pressure system that has played the major role in the weather pattern over the last several days is currently centered over the southern half of the state where it will remain today. With only minor movement of this low expected today, the weather should remain similar to Friday weather. One inch plus precipitable water values and unstable conditions will ensure another afternoon and evening of mountain thunderstorms at least over the Sierra Cascade range.
Some of these thunderstorms could produce brief periods of heavy rainfall. Little airmass change will mean another day of high temperatures a few to several degrees above normal. The upper low shifts a little southward on Sunday as weak high pressure pushes in over the north state. This puts NorCal into upper level diffluent flow and another round of afternoon showers or thunderstorms over the mountains.
Airmass warms a bit on Monday as the weak upper ridge pushes inland. Forecast highs on Monday are forecast to top out close to 10 degrees above normal. Diffluent flow aloft will continue the afternoon thunderstorm threat over the Sierra Cascade range.
Daytime highs on Tuesday nudge up a bit more as weak upper ridging pushes in across NorCal. Substance under the ridge should reduce the mountain thunderstorm potential but still can not rule out isolated thunderstorms over the northern Sierra.
Extended Discussion (Wednesday through Saturday)
Upper ridging weakens and shifts east Wednesday as troughing deepens along the West Coast. Heights and thicknesses continue to lower Thursday into Saturday as upper low moves into the PacNW.
Main impact for interior NorCal will be a cooling trend with increasing onshore flow and deepening marine layer.
High temperatures go from about 10 degrees above normal Wednesday to several degrees below normal by Saturday.