August 15, 2018 – Dry with near normal temperatures through Thursday, then above normal Friday through early next week. Smoke impacts from wildfires continue.
Interior NorCal sandwiched between upper troughing off the West Coast and high pressure over the Desert SW. Monsoonal moisture continues to lift north through the CWA, and 88D showing some light returns over Eastern Shasta county attm. Higher resolution models indicating moisture and threat of showers will lift north of the CWA early this morning. Flow through the Carquinez Strait has been strong overnight with marine layer about 2k ft deep. Expect some stratus will advect through the Delta area this morning. Short wave trough approaches the West Coast today with continued enhanced onshore flow. High temperatures forecast to be near to slightly below normal.
Secondary upper trough approaches the NorCal coast Thursday and moves through into early Friday. Onshore flow forecast to weaken some Thursday allowing for minor warming in Delta breeze influenced areas. Little change in high temperatures expected elsewhere across the CWA Thursday.
Heights rise Friday as shortwave upper ridging approaches, then moves through Saturday. Warming expected over the forecast area Fri/Sat with highs increasing to above normal. Widespread triple digit max temperatures return to the Northern Sacramento Valley Saturday with upper 90s elsewhere in the Central Valley.
Extended Discussion (Sunday through Wednesday)
NorCal will start out extended period under upper level southwest flow between high pressure over the southwest U.S. and a weak trough over the northeast Pacific. This stable pattern should keep any showers or thunderstorms out of the forecast. Despite onshore flow aloft, airmass will remain warm enough for daytime highs to remain a few degrees above normal. A slight cooling takes place early to mid next week as the weak system off the Pac NW coast unsuccessfully tries to push inland.
Even with the slight cooling Monday and Tuesday, daytime highs remain a few degrees above norms. Little change on Wednesday as Southwest U.S. ridge holds strong. Kept haze in forecast across CWA through the extended period as fires over NorCal showing no signs of going away in the near future.