November 21, 2017 – Mainly dry weather this week with rain chances limited to far northern CA. Wetter system possible early next week.
High pressure has begun to build into California from the south, bringing clearer skies and forcing the upstream atmospheric river northward. A few light showers are still present mainly along the northern CA coast. Nighttime satellite imagery suggests extensive coverage of low stratus with some fog across the region. Northerly surface winds are keeping fog from becoming dense thus far however.
Warm temperatures with mainly dry weather are expected the next couple of days under strengthening high pressure. Look for high temperatures to reach the upper 60s to lower 70s across the Valley, with 50s and 60s over the mountains. These forecast high temperatures are 5 to 10 degrees warmer than normal for this time of year, and may be within a couple of degrees of record high temperatures.
With clearing skies and light winds, Valley fog may develop over the next few mornings. The most likely areas will be from around Sacramento southward, and favored mountain basins.
A weak weather system may make its way into NorCal on Thanksgiving, and may bring a few showers to the region. This isn’t expected to significantly impact holiday travel however.
Extended discussion (Saturday through Tuesday)
Shortwave will move through the area on Saturday into early Sunday. Majority of moisture plume will be pointed toward the Pacific NW so local area will just catch the tail end of precipitation. Shower chances will be mainly for I-80 northward with heaviest amounts in the mountains. Still not a big soaker by any means and snow levels will remain high.
Parent low and associated trough will then approach the area Sunday night and move through on Monday. Models are in better agreement than past several runs so confidence in forecast is increasing, though still some uncertainty with precipitation amounts. Regardless, this system should bring better chances for more widespread precipitation, again heaviest amounts in the mountains. The difference with this wave is that snow levels look to drop below pass levels on Monday as colder air moves in. This will bring accumulations down to 5000-6000 feet and possible travel delays over mountain passes. Mild temperatures expected for the weekend, cooling off a bit by Monday.