March 15, 2021 – Showers will linger across the region today, especially over the mountains where difficult travel conditions will persist. Dry weather is forecast for Tuesday and Wednesday before renewed precipitation chances return on Thursday.
Discussion
Satellite imagery shows the cold mid/upper low closing off over NorCal early this morning as the trough gradually moves southeast. Radar indicates moderate, to occasionally heavy, precipitation continuing over the west slopes of the northern Sierra, but widespread precipitation has mostly cleared out of the Central Valley. Caltrans traffic cameras indicate significant accumulating snow on many of the mountain highways, especially in across the northern Sierra.
The system will drop southeastward across the region today. HREF still indicating several more hours of 1-2 inch/hour snowfall rates over the northern Sierra/southern Cascade Range this morning. However, HREF and CAMS indicate a general trend toward decreasing snow over the northern Sierra by mid to late morning, so if trends follow the guidance we may be able to drop some of the winter weather products a bit earlier. Stay tuned.
CAMS indicate scattered showers will accompany the low as it moves south today, so renewed shower threat will be possible across the Sacramento region around late morning into the early afternoon. At this point, it`s looking like the main chance for isolated thunderstorms will be later this afternoon across the southern Motherlode as the system drops south. Small hail and brief heavy rain would be the primary threats.
Dry and milder weather returns for Tuesday and Wednesday, though temperatures will still be a little below average for mid-March. The next system approaches Thursday, but cluster analysis of the ensemble data indicate that most precipitation will likely hold off until later Thursday or Thursday night when travel impacts will likely return to the higher elevation roads.
Extended discussion (Friday through Monday)
Upper level troughing will be set up along the west coast for the start of the extended period. The best chances for precip look to come Thursday night into Friday as a cold front tracks through the area, although ensembles are struggling with the timing and we may see this change.
Shower chances are going to continue on Friday as the trough axis pushes through. Mainly dry weather is then expected on Saturday with additional shower chances mainly over the mountains on Sunday as short wave trough tacks into the PacNW and just to our east. With the troughing in place we will see cooler than average daytime highs.