SOUTH LAKE TAHOE, Calif. — After a rather balmy Christmas Day on Sunday, a robust multi-day storm next week is expected to tap into a warm atmospheric river that will pack strong winds, heavy precipitation and likely lead to travel difficulties at Lake Tahoe.

“Santa may be a tad confused as he rolls up to the warmest weather we’ve seen thus far in December,” said the National Weather Service in Reno which forecasts high temperatures on Sunday to be in the low 50s. “But ‘tis is the season for dramatic weather pattern changes.”

NWS Hydrologist Tim Bardsley said the storm next week will be “wet and warm” and won’t add much to the snowpack, but will give dry soil beneath the snow much needed moisture. 

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Bardsley said this year’s snow has fallen onto pretty dry soil and “when [that happens] we kind of have to satisfy that soil moisture deficit before we get a run off.”

“The dry soil beneath the snow is like a sponge and will mitigate excessive runoff from the event next week,” Bardsley said. “From a water supply perspective, we will end up getting less runoff for the same amount of rain with damp soil.”

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Ridgetop winds will begin increasing on Monday and gusts may get up to 70 to 100 mph. Moving Tuesday into Wednesday, the service said stronger gusts will easily eclipse 100 mph.

The NWS is confident that heavy moisture will push into the basin from Tuesday through the end of the year, but the kicker is snow levels and snow ratios and how they fluctuate during the storm.

Snow levels are expected to start at about 8,000 feet before dropping Tuesday evening.

As of Thursday, the NWS is forecasting through Wednesday night, Dec. 28, a 60-70% chance of two feet of snow along the Sierra crest above 9,000 feet, a 20-40% chance for a foot along the crest above 7,000 feet, including Donner Pass and a 25-35% chance of at least 6 inches at lake level, including Truckee. 

“A major caveat needs to be mentioned, especially for the 6,000-8,000-foot range,” the service said. “The exact thermal profile is subject to change which may significantly affect the snow totals in these areas. What is more certain is this will be wet/cement-like snow with low ratios. If your plans take you into or across the Sierra next week, keep an eye on the forecast and be prepared to adjust plans accordingly.”

Some of the rain will be retained in the snowpack and some will be run off with some melting at the lower elevations. Certainty of the impact on the lake levels and snowpack and dialed in snow forecast will become more certain as the system moves closer.

Ashleigh Goodwin can be reached a agoodwin@tahoedailytribune.com. Bill Rozak can be reached at brozak@tahoedailytribune.com.