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October 18, 2021 – Decreasing shower chances this morning, otherwise dry and cool through Tuesday. Precipitation chances return Tuesday night and continue through at least this weekend.
Radar shows most of the precipitation associated with the front has moved southeast of the forecast area while scattered to numerous showers continue over the northeastern third of the forecast area beneath the mid/upper low as it closes off. Significant snow has occurred across the northern Sierra since Sunday evening impacting travel over the higher passes (KBLU at about 5k ft elevation has picked up an estimated 5 inches). Precipitation amounts have varied from a few hundredths of an inch up to a quarter inch in the valley, while much of the northern Sierra and southern Cascades have seen a half inch up to an inch.
The low is forecast to move quickly southeast into the Great Basin today. Most remaining showers will end this morning, though a few will linger over the northern Sierra into the afternoon. Most of the significant snowfall in the northern will be over early this morning, but lighter snow showers may continue into midday over the higher elevations.
Dry weather expected tonight and Tuesday, then another system will spread precipitation across the area Tuesday night and Wednesday. This one will tap deeper moisture to our southwest and may result in moderate amounts of QPF over the region on Tuesday night as a frontal system stalls out over NorCal. Snow levels will be considerably higher than the current system limiting impacts to travel.
Warm-advection likely to continue lighter precipitation Wednesday and Thursday, mainly to the north of I-80.
Extended Discussion (Friday through Monday)
Pacific frontal system with associated 1-1.5 PWS moves through Friday. Moderate to locally heavy precipitation is possible.
Precip ramps up again over the weekend into Monday as models indicate a 170+ kt zonal polar jet stretched across the Pacific with LFQ extending over NorCal.