May 31, 2020 – Threat of showers and afternoon thunderstorms will continue over the Sierra Nevada through the upcoming week. Warming trend with high temperatures climbing to 10 to 15 degrees above normal by Tuesday.
Upper troughing along 130W will send embedded disturbances across interior NorCal later today into this evening. Models generate some precip over the higher elevations of the Sierra during this period. Otherwise dry weather expected across the CWA today with varying amounts of cloudiness. High temperatures forecast to be near normal with low to mid 80s in the Central Valley.
Upper troughing develops closed low off the SoCal coast Monday while higher latitude portion progresses into the PacNW. Interior NorCal becomes setup under upper level COL. Afternoon precip threat not only includes the higher elevations of the Sierra Nevada Monday, but also over portions of the Shasta mountains. A few degrees of warming expected tomorrow.
Closed upper low remains quasistationary off the SoCal coast Tue and Wed as zonal flow sets up across the PacNW. Mid level southerly divergent flow into the southern CWA will keep a threat of afternoon deep moist convection over the Sierra Nevada. Forecast CAPE values support the potential for afternoon thunderstorms over that area. Decreasing cloudiness over remainder of interior NorCal with height/thickness rises will raise high temperatures upwards of 10 to 15 degrees above normal. Mid to upper 90s expected in the Central Valley Tue/Wed with 70s to around 90 for the mountains and foothills.
Extended Discussion (Thursday through Sunday)
High temperatures about 10 degrees above normal continue on Thursday as Four Corners ridging extends into NorCal. This means highs in mid to upper 90s for the Valley, foothills mid 80s to mid 90s, mountains in the 60s to around 80. Heat Risk levels will be at Moderate levels for those sensitive to heat. Anyone planning be outdoors should avoid the hottest period of the day.
Ensembles and deterministic models continue to show a cutoff low just off the southern California coast gradually moving inland late Thursday into Friday. Embedded shortwaves along the northern portion of the low could produce mountain shower and thunderstorm chances on Thursday, but these should be limited mainly to the Sierra south of I-80.
Ensembles continue indicate a trough approaching from the Gulf of Alaska Friday. GEFS and EPS continue to show cooling trend, with high temperatures near normal levels. There is also a chance of precipitation by later Friday for the northern mountains, with some showers potential still lingering over the Sierra south of I-80. The best potential for showers is on Saturday, focused over the northern mountains, but could extend through much of the Sacramento Valley and into the Sierra. The weekend looks relatively cool, similar to what we just saw this past weekend.