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Gusty wind, rain, and heavy mountain snow continue today as a storm moves across the area. Mountain travel will be hazardous twith whiteout conditions, chain controls, and road closures possible. A short break may be seen in precipitation late Tuesday before additional rain and and mountain snow return Wednesday into Thursday. Locally low snow levels possible Wednesday morning.
Ongoing precipitation due to the Atmospheric River event will continue to push through the region as the trough continues to trek eastward through the day. Amplifying mid-level trough off the West Coast will sharpen this aftn as a potent vort lobe swings through the base, driving the entire trough onshore this evening. This trough is progged to close off Wednesday near the Four Corners before ejecting into the Plains, with brief mid-level ridging filling in its wake.
Thereafter, yet another potent trough, this one likely manifesting as a closed low dropping along the British Columbia Coast, will surge southward into Oregon Thursday morning bringing yet another round of heavy precipitation to NorCal.
A PW plume will be advecting onshore wed night/thu with the next system. Snow levels within, and in the vicinity, of the most robust IVT will climb to around 5000 ft briefly south of highway 50 Wed night/Thursday morning and could limit lower elevation snow amounts.
However, elsewhere, snow levels will be quite low, down to 2000 ft at times. During the wed night/thu period the heaviest accumulations are once again expected in the Sierra and Southern Cascades where ensemble probabilities for 12 or more inches are high, and locally 2 feet is possible.
Have seen snow levels fall to 1500 feet into Sierra foothill communities like Grass Valley, Colfax and Placerville this morning with snow accumulations from 1 to 5 inches likely and have extended the winter storm warning down to these locations through 6 am.
Snow band will diminish to showers through the morning, although may see some convective enhancement during the afternoon. A brief break with dry weather tonight before quick moving cold system brings another round of heavy mountain snow Wednesday and Thursday.
Have issued a winter storm watch from Wednesday morning through Thursday for much of the southern Cascades and northern Sierra. Where another 1 to 2 feet is possible, especially above 3500 feet, could also see several inches in the 2000 to 3500 feet range.
Redding and lower elevations could start out as snow, but timing of the system during the day may hamper cold air drainage needed for a heavy Redding snow event, so will keep best heavy snow probabilities Lake Shasta northward. Breezy winds with a few gusts up to 35 mph will also be possible up the Valley Wed aft/Thu mrn.
Extended Discussion (Saturday through Tuesday)
Models in better agreement with next Pacific frontal system moving into the CWA Saturday into Saturday night with another round of widespread precipitation.
Sunday looks mainly dry as short wave ridging moves through. Models then differ with handling of next upstream system. NBM leans towards GFS solution with more widespread precipitation predicted Monday into Tuesday.