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A significant storm will bring rain, wind and very heavy mountain snow Sunday through Tuesday. Mountain travel will be hazardous Sunday through Tuesday with chain controls and possible road closures. Winter Storm Warning in effect from 10 PM this evening to 10 PM Tuesday.

Discussion

Brief ridging period over NorCal today with all eyes on storm system up stream over Gulf of Alaska. Cold temperatures again this morning with widespread readings in the low 30’s with widespread areas of frost. Slightly below normal high temps ranging from the upper 40’s to low 50’s today.

Strong upper jet streak and vigorous shortwave energy diving southeastward from the Gulf of Alaska will further amplify the deepening low across the northern Pacific, as the longwave trough pivots closer to the central-northern West Coast Sunday. The amplification of the upstream trough/downstream ridge will cause the low-mid level flow to back south to southwest, allowing an atmospheric river to press southward along the central CA coast into the Central Valley with precipitable water values around 0.75-1.00″.

Powerful upper jet 130-150kt will provide large-scale ascent that will be enhanced on upslope flow into south to southwest facing slopes. Rainfall Sunday through Tuesday will average 2-5″ Valleys, with higher amounts (3-6+ inches) over mountains and foothills.

Burn scars in the higher terrain above 4000 feet will have snow as the dominant precipitation type and are not expected to be significantly impacted at this time.

Valley impacts from rainfall look to be nuisance poor drainage flooding and small stream rises at this time.

Snow levels will generally be in the 3500 to 5000 ft range Sunday and Monday, then drop to 2000 to 4000 ft Monday night and Tuesday (lowest snow levels north in Shasta.

Total snow accumulations will be tremendous. Easily the biggest snowstorm so far this season. Expect widespread snow totals in the 2 to 5 foot range in the Sierra Nevada above about 3500 or 4000 ft elevation.

Strong southerly winds with accompany this storm. Valley winds with gusts of 35 to 50 mph are expected. Winds will increase on Sunday and likely peak on Monday.

Widespread hazardous travel

Travel will become dangerous, especially for the mountain passes, and is discouraged. Roads through the passes are likely to experience chain controls and possible closures. Whiteout conditions, downed trees, and power outages are all possible.

Extended Discussion (Wednesday through Saturday)

There won’t be much of a break in precipitation as the first storm departs and the next system arrives by early Wednesday, just a brief lull in intensity. Snow levels drop further, though, as more cold air advects in, down to around 1500 feet and potentially lower.

Snow showers behind the trough and with another Gulf of Alaska trough could bring additional hazardous travel conditions through Wednesday.

Another couple feet of snow are possible in the mountains, with a few inches into the upper foothills. Some light accumulations could even extend into part of the northern Sacramento Valley.

Gusty southerly winds are also possible Wednesday night into early Thursday.

Thursday will see additional precipitation across the area as the trough moves inland, with around another foot or so in the mountains. Friday has trended drier, with better confidence for ridging.

A week system brushing to the north could bring some light precipitation Saturday to the northern mountains and northern Sacramento Valley.