January 17, 2020 – Showers taper off across the region early today. Mainly dry and milder weather is expected over the weekend before precipitation chances return next week.
Radar indicates light to moderate snow showers continuing early this morning across the west slopes of the northern Sierra and southern Cascade Range. Heavier showers may bring additional snowfall accumulation rates of up to an inch/hour until around sunrise. Precipitation has ended across the remainder of the area.
The upper trough lifts into the northern Rockies this morning as short-wave ridging moves over NorCal. Remaining showers over the Sierra are then expected to diminish quickly in the morning. Some light precipitation may linger across the mountains of northern Shasta county into this evening as warm-advection and moisture convergence increase ahead of the next system.
Satellite imagery shows a maturing extratropical cyclone off the coast of the PacNW. This system will give the far northern portion of the forecast area a chance of precipitation on Saturday as it moves ashore well north of the region. Otherwise, dry and milder weather is forecast across the area through the weekend.
Next chance of more widespread precipitation returns next week (later Monday) as another trough approaches the West Coast.
Extended Discussion (Tuesday through Friday)
Unsettled weather is expected through the extended period.
The GEFS is trending toward the slower onset of the next significant system early next week, as the ECMWF ensemble has been showing in the past few runs. This suggest the bulk of the precipitation will be timed for Tuesday. This is a warmer and somewhat less wet system than the one currently impacting the area. Snow levels are currently expected to be around Blue Canyon’s elevation (5280 feet), so impactful snow should be mainly above 6000 feet. Early estimates of snowfall are around a foot to a foot and a half. Anyone planning travel over mountain passes should be prepared for possible delays and chain controls. This is a fairly quick moving system, with Valley rainfall amounts of around a quarter to three quarters of an inch. By Wednesday, just lingering showers are forecast, mainly over the mountains. Thursday into Friday another system could bring mainly light mountain precipitation, but confidence is low. The best potential for precipitation is over the northern mountains.