September 8, 2019 – Cooler temperatures through Tuesday with below normal temperatures. Warming Wednesday with near to slightly above normal temperatures returning Thursday into Saturday. Slight chance of showers over the Shasta mountains Monday afternoon. Increased threat of showers and afternoon thunderstorms over the mountains, and possibly Northern Sacramento Valley, Tuesday.
Upper trough has shifted east into the Great Basin along with associated cloudiness. Minor upper ridging will move through today in northwesterly flow aloft. Weaker Delta breeze will allow for slightly warmer temperatures today compared to areas influenced by the stronger onshore flow yesterday. Remainder of the CWA expected to see cooler max temperatures in response to post trough AMS.
Deeper troughing moves over NorCal Monday and Tuesday bringing additional cooling. Models suggest the potential for showers over mainly Shasta county late in the day Monday. Overall dynamics and synoptic UVM increases over the CWA Tuesday as 560 DM upper low moves into the PacNW. Threat of showers and afternoon thunderstorms becomes more widespread over the mountains Tuesday, generally from a KUKI-KBLU line northward. May even see showers extending into the Northern Sacramento Valley. High temperatures bottom out Tuesday with forecast values upwards of 10 to 15 degrees below normal.
Upper troughing shifts into the Great Basin Tuesday night into Wednesday morning. Upstream upper ridging from the EPAC builds inland over NorCal Wednesday. This will result in dry weather with warming temperatures, however highs expected to remain about 2 to 5 degrees below normal.
Extended Discussion (Thursday through Sunday)
Ensemble guidance is in good agreement with ridge rebuilding across the region later in the week. Dry weather expected with temperatures returning to above average.