December 29, 2020 – Dry weather expected through Wednesday afternoon with possible valley fog this morning and Wednesday. A weak system will bring light precipitation Wednesday night into Thursday. Active pattern is possible for the New Year’s Holiday weekend.
Low pressure area over the Southwest with high pressure building over Northern California. North winds over the far north end of the valley is helping to keep temperatures warmer while further south winds are light and temperatures have been cooling off much faster where we should see frost in the morning. Patches of light fog trying to form this early AM so will keep an eye out for possible dense fog formation from around Marysville southward and from the Sacramento river eastward.
The same fog watch will occur for Tuesday night. The only difference is that some clouds will move over the area at night that may help limit fog formation and less north wind for some places. Cold morning lows this morning and Wednesday with lows in the upper 20s to mid 30s for most of the valley to the teens and single digits for the mountain valleys.
High pressure will remain with us through Wednesday then a weak system will move through Wednesday night and Thursday morning. The models have been trending this system weaker just like the last one so may not need any advisory for snow as we get closer to the storm. Currently forecasting 1-3 inches of snow. Snow levels will get low 2500 to 3000 ft over Shasta County to 3500 to 4000 feet elsewhere. Valley rain less than a tenth if any.
Behind the weak system high pressure will rebuild and we can expect dry weather through New Years Day. Only a small chance for the northwestern areas for some precipitation at this time. (Northern coastal range through Shasta County)
Extended discussion (Saturday through Tuesday)
Big differences in the models for the Saturday and Sunday system. GFS is much weaker than the European model and initially does not indicate as much aerial coverage. Both do indicate most of the area getting something late Saturday night and Sunday morning. The range in output currently ranges from a non-impactful storm to an impactful one so confidence is low with this system on the details at this time.
Another system follows late Monday into Tuesday that both models indicate a possible impactful storm.