November 15, 2019 – High confidence in dry and mild forecast through early next week. Very warm over the weekend with record highs possible in north Sacramento Valley. Pattern change still on track around mid week with some breezy winds and cooler temperatures forecast.
Early this morning, clouds have begun to overspread the area as a trough moved onshore. Radar has picked up on isolated, light reflectivities over the northern Shasta and coastal mountains with this passing system, with only light showers expected through the morning. in the southern Sac Valley, some low stratus and mist have been noted and is expected to dissipate around mid-morning.
The trough splits late Friday with a cut off low forming just off the coast of SoCal Friday night, and the northern portion digging into the Central great Basin Saturday.
Ridging builds back into northern California at this time, remaining through the weekend. Winds pick up across the northern Sac Valley and foothills Saturday with some gusts up to around 25 mph possible mainly in the afternoon.
Temperatures will be roughly 5 degrees above average this afternoon, increasing significantly by Sunday and Monday with afternoon highs around 10 to 20 degrees above normal. Valley lows each night will be in the 40s, with mountain lows in the 30s.
Extended discussion (Tuesday through Friday)
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By Tuesday, a notable shift in the pattern takes place as a closed low nears the Pacific Northwest coast early in the morning. While a core of the height falls advances toward the upper Intermountain West, some of this energy dips south toward the California/Oregon border. How this evolves will ultimately dictate the impacts across the region which likely includes a period of gusty north to northeasterly winds and a few mountain showers. Recent ensemble means support a southward track of the upper low while reaching southern California by Thursday before exiting toward the Four Corners region.
While ensemble spread exists with this system, there is a fairly high signal in the guidance for the mentioned dry, gusty winds from Wednesday into early Thursday. ECMWF ensemble probabilities show fairly high percentages of gusts exceeding 35 mph along the western side of the Sacramento Valley as well as the foothills and higher terrain. With decreasing humidities in this flow regime, fire weather concerns will need to be closely monitored given historically dry fuels for mid-November. Given strong forcing underneath the low center, some scattered mountain showers will be possible. Overall, keep in mind any shift in the upper low track will alter impacts over the area. Stay tuned for updates on this forecast in the days ahead.
Regarding temperatures, a cool down will occur in this pattern but still remains roughly 4 to 8 degrees above average. This equates to Valley highs regularly sitting in the mid to upper 60s while 40s and 50s will be more commonplace in the mountains.