June 1, 2020 – Threat of showers and afternoon thunderstorms will continue over the mountains this week. Warming trend with high temps climbing to 10 to 15 degrees above average by mid-week, then cooling with an increased chance of showers by the weekend.
Discussion
Partly to mostly cloudy skies cover the region early this morning as a weak trough moves across the area. Current temperatures are milder compared to 24 hours ago and generally range from the upper 40s and 50s in the mountains, to the 60s to around 70 across the Central Valley.
Mid/upper level COL develops across NorCal today and continues into mid-week as the trough splits with a cutoff low dropping south to off the coast of SoCal as westerlies retreat north into the PacNW and ridging builds in from the eastern Pacific and the Desert Southwest. This will result in a strong warming trend across the region which will likely peak Wednesday/Thursday when valley temperatures return to around the century mark.
A few late-day terrain induced showers and thunderstorms will be possible across the NorCal mountains today, then activity is expected to be limited to the Sierra Nevada south of Lake Tahoe for Tuesday thru Thursday.
Extended Discussion (Friday through Monday)
Quasi-stationary closed upper low that has been off the SoCal coast is forecast to progresses inland Friday. At same time, higher latitude short wave system approaches NorCal. Precip threat exists over the mountains Friday then over much of interior NorCal overnight into Saturday. Main offshore upper low keeps a threat of showers going Sunday, north of I-80 and mainly over the mountains. Upper low weakens as it moves across northern portions of CA Monday keeping a threat of showers over the Shasta mountains. Significant cooling expected over the weekend with below normal temperatures Saturday through Monday.