June 12, 2019 – Gradual cooling trend through the remainder of the week, but above normal temperatures continue into next week. Threat of an afternoon shower or thunderstorm will be possible over portions of the mountains through Monday.
Discussion
High amplitude upper ridging along the West Coast will gradually be replaced by upper troughing over the next 24 hours. Upper ridging then discontinuously retrogrades offshore and resides near 120 W through Friday while broad upper troughing lingers over NorCal through the weekend.
This pattern change will result in a downward trend in high temperatures into Friday then rising slightly over the weekend. High temperatures however are forecast to remain about 5 to 15 degrees above normal. Onshore flow will be on the increase by this afternoon with moderate to strong Delta breeze expected tonight into Thursday, persisting into the weekend.
Models depict increased CAPE over the Coastal range through Thursday, over Lassen Park through Friday, and over the Northern Sierra Nevada through Monday for a slight chance of afternoon to early evening showers and thunderstorms.
Extended Discussion (Sunday through Wednesday)
A few late-day showers or thunderstorms over higher terrain could be possible early next week mainly for areas south of HWY 50; elsewhere, dry conditions will prevail. Warming returns to the region early next week as ridging from the eastern Pacific extends into NorCal.
Look for highs in the mid to upper 90s in the Valley; triple digits possible mainly across the northern Sacramento valley. These forecast highs range from 6 to 12 degrees above normal.