Partly cloudy skies cover the region early this morning. Winds are light across most of the area except for some local lingering east winds of 15-25 mph over the northern Sierra foothills. Current temperatures range from the mid 20s in the mountain valleys to the lower to mid 60s across the milder foothill thermal belts. Central Valley locales are mainly in the mid 40s to lower 50s.
The persistent West Coast ridge will shift east over the next couple of days as the upper trough off the coast approaches and then moves onshore later Thursday into Friday. Lots of mid and high level cloudiness will spread across the region (even more than what we’ve seen over the past few days), and combined with synoptic cooling from weakening high pressure, will lead to cooler temperatures through the end of the work week (though still above average for mid-November).
Pattern repeats itself beginning this weekend as Rex Block redevelops along the West Coast leading to a return of warmer temperatures and likely some daily record highs in jeopardy.
Extended Discussion (Sunday through Wednesday)
A powerful upper ridge will be in place to commence the weekend with 500-mb height anomalies in the 1.5 to 2 standard deviation range. Projected heights may reach 590-dm on Sunday which is quite impressive for the time of year. The accompanying 850-mb temperatures of 18C would support highs well in the 80s in a well mixed atmosphere. However, such an environment is often unattainable deeper into the cool season so Valley highs from the mid 70s to low 80s are more likely. Relative to climatology, this is roughly 10 to 20 degrees above average. With a daily record high in Redding of 83 degrees (dating back to 1893), would not be surprised to see this either tied or broken. Well above average readings will continue into Monday given the ridge lingers yet another day.
From Tuesday into later in the week, the upper ridge will finally have advanced into the Rockies. A seasonably strong trough enters the picture while accelerating through the Pacific Northwest early Tuesday. While a few ensemble members support the trough taking a farther west track bringing some scattered showers to the region, a vast majority carry the system through the Central Great Basin instead. The latter scenario would favor an uptick in northerly gradients which lowers humidities and enhances wind fields. Given this trough remains nearly a week out, it will need to be closely monitored for any notable impacts. In the meanwhile, high temperatures from Tuesday onward should be noticeably cooler, but still roughly 3 to 6 degrees above average.