Incoming atmospheric river prompts winter storm warning in parts of Utah this weekend

SALT LAKE CITY — Parts of Utah are in line for some heavy snow after a relatively dry January.

The National Weather Service has issued a winter storm warning for the Wasatch and Western Uinta mountains, which could receive up to 2 feet of snow or more over the weekend and into early next week. The agency also issued winter weather advisories that cover Wasatch Back and the central mountains, which are expected to see strong snowfall as well.

The storm is also projected to deliver heavy rain totals in the valleys, especially across the northern half of the Wasatch Front and northern Utah.

It may be just the beginning, too. Long-range projections indicate two or three more storms could impact the state, potentially reaching wider parts of the state, KSL meteorologist Matt Johnson says.

"What we can draw from this is it looks like the start of an active pattern," he said.

Unseasonably warm temperatures are also forecast for next week.

Storm timing

A "warmer and milder" low-pressure system dropping into California is forecast to enter Utah on Friday as it moves east. Johnson said precipitation will begin to enter parts of northern Utah sometime in the late afternoon and early evening.

Storms will pick up overnight into Saturday, bringing a "nice plume of moisture" to northern Utah and the Wasatch Front throughout the day, Johnson said. The mixture of valley rain and mountain snow is also forecast to continue into Sunday and possibly into Monday.

However, not all weather models agree on which Utah areas will receive snow.

Johnson said the core of the decaying atmospheric river is expected to be in British Columbia, Canada, but some models show it could dip as far south as northern Oregon. That difference will likely impact who in Utah receives moisture from the storm.

"It's been a forecasting headache because not all models are on board with the idea of bringing that band of rain — that atmospheric river — as south into the Wasatch Front," he said. "Some have it reaching Provo, some have it just clipping Salt Lake City ... because there's differences in what each model is saying."

Projected accumulations

The Wasatch and Western Uinta mountains are projected to receive 1-3 feet of snow between late Friday and Monday afternoon, according to the National Weather Service's winter storm warning updated on Friday. The agency adds that higher totals — possibly up to 5 feet of snow — are projected for the Bear River Range in northern Utah.

The central mountains are forecast to receive 6-12 inches, while Wasatch Back communities could end up with 2-7 inches, according to the advisories. Johnson said the latter is tricky to estimate because the snow line is projected to jump from about 5,500 feet elevation on Saturday to about 8,000 feet elevation by Sunday morning because of how warm the storm is.

The warnings and advisories note that travel will likely be tricky along mountain passes, and traction laws could be enforced in some areas. Johnson adds that avalanche danger will likely increase in affected areas.

Valley communities could pick up strong precipitation numbers, as well. A KSL Weather model updated Friday afternoon indicates that many communities, particularly north of Salt Lake City, could receive over an inch of precipitation or more over the weekend. The rest of the Wasatch Front and parts of central Utah could end up with 0.20-0.60 inches.

However, Johnson said weather models had offered different outcomes depending on the storm's dynamics.

Just the beginning?

No matter what the groundhog says on Sunday, it will feel like early spring after the storm. High temperatures are forecast to reach the upper 50s and low 60s across the Wasatch Front and low 70s near St. George before the next system.

Long-range outlooks indicate more precipitation-heavy storms will likely impact Utah's northern half, but those could impact wider swaths of the state over the first half of February. A projected cold front in the second half of next week could mix in, so it's unclear if those will produce valley rain or snow just yet.

"Not all models are saying that, but I do think we'll have some valley snow chances," Johnson said.

He said various models also indicate the Wasatch Mountains could receive 5-8 inches of snow water equivalent, which could translate into several feet of snow.

That's a big development for Utah's lagging snowpack, which has now fallen to 76% of the median average for late January statewide. Nearly all basins, including in northern Utah, have now fallen to between 90%. Snowpack in southwestern Utah, which isn't forecast to be affected this weekend, has fallen to record-low levels.

Utah's snowpack and spring snowmelt process accounts for about 95% of the state's water supply.

"We love the water content because the last several storms have been moisture-starved, puny storms," Johnson said.

Full seven-day forecasts for areas across Utah can be found online, at the KSL Weather Center.

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