Discussion
Our current weather system continues to trek along the California coast as it drops down from the Pacific NW today through Thursday PM. Compared to Sunday's system, this system is tracking further south with a warmer airmass associated with it. This translates to a weaker thunderstorm signal for our area and lesser chances for snow along the peak of the Sierra. Current probabilities show a 15-40% of thunderstorm development over the Sierra and adjacent foothills with highest chances (30-40%) along the ridge of the Sierra this afternoon and evening (Wed 21z - Thu 03z). Forecast show around 0.10-0.50 over the Sierra and foothills, up to just under an inch along the Sierra crest. Probabilities of exceeding 0.25" for the aforementioned area are 55-85% over the Sierra with 30-50% over the foothills. The northern Sacramento Valley and lower portions of the Valley south of I-80 (below 1000 feet) have 10-30% chance, which is more so indicating the slight chance of showers moving through the Valley than any organized stratiform precipitation.

This weather pattern will bring another chance of debris flow issues over the Park Fire burn scar, albeit less synoptic support compared to last weekend. A few hi-res model simulations show isolated thunderstorms tracking over the northeastern portion of the burn scar early Wednesday afternoon from east to west until Wednesday evening around 8pm local.

As this system moves further into Southern California on Thursday, we'll see another round of thunderstorm chances confined to the Sierra crest during the afternoon and evening hours. NBM probabilities have 15-30% along the Sierra crest, with the highest chances south of US 50. Given the center of the low being further south, this will result in more southeasterly steering flow and downslope storm motion.

By Friday, heights are expected to rise behind the weather system, returning temperatures to near normal by weekend's end.
Friday will see afternoon highs warm to the mid 80s to low 90s in the Valley with upper 60s to mid 80s across the mountains to foothills areas. With the warming temperatures and reoccurring light to breezy north winds in the Valley through the weekend, daytime humidities lower back to 20-30% over the Northern Sacramento Valley through the weekend and into early next week.

.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)...
Dry weather is expected through the extended forecast period as cluster analysis and ensemble guidance indicate high pressure extending inland over Northern California. Temperatures will warm up through the weekend and into early next week with highs in the mid to upper 90s across the Valley and Delta. Areas of Moderate HeatRisk also return to the Delta, Valley, and foothills of the Sierra Monday-Tuesday as temperatures rise 5-10 degrees above normal.
By the late weekend, the previous weather system will be located just south of the Great Basin resulting in periods of light to breezy northerly flow across the more windprone areas of the Sacramento Valley (i.e. the northern Sac Valley and along the I-5 corridor in the Sacramento Valley) Sunday through Tuesday. Daytime humidities will decrease gradually through this period into the upper teens to upper 20s, which may lead to localized fire weather conditions in the northern Sacramento Valley and adjacent foothills. An onshore flow pattern looks to return to interior NorCal by Wednesday, alongside slightly cooler temperatures as weak upper level troughing begins to set up offshore.

AVIATION
Mainly VFR conditions and surface winds below 12 knots over interior Northern California during the next 24 hours. Isolated MVFR/IFR conditions may occur due to scattered rain showers and isolated thunderstorms over the foothills and Sierra (between 22z Wed-08z Thurs). Over the Sierra, easterly wind gusts up to 20 knots will be possible this evening (04z-09z Thurs).

STO WATCHES/WARNINGS/ADVISORIES
None.