An atmospheric river is moving through the West. How will it impact Utah?

SALT LAKE CITY — This month has already been great for Utah, and an atmospheric river moving across the West this weekend could add to it, but it may not be as beneficial as forecasts initially believed.

National Weather Service offices across the Pacific Northwest and other parts of the West issued a series of winter weather advisories as an atmospheric river — long, narrow regions of abundant water vapor moving through the sky — moves through the region, bringing “lower elevation heavy rain and mountain snow.”

Alerts were issued for parts of Oregon, Washington, Idaho and Montana, where over a foot of snow was possible in places like Mount Rainier, and some parts of those states could receive their first snow accumulations of the year as it moves east. However, it’s expected to lose some of its structure and become “mainly a northern Utah event” as it reaches the Beehive State over the weekend, KSL meteorologist Matt Johnson says.

“This is a cherry on top for October,” he said.

Storm timing

The incoming atmospheric river has the type of organization, dynamics and moisture levels to be “a good producer” for the Pacific Northwest, but it’s forecast to become a little more unorganized as it moves east, Johnson explains. Models initially hinted that its core could slam into the state, but models now project that its southern boundary will skirt by the Wasatch Front and northern Utah.

Clouds are forecast to filter into the state on Saturday before the system begins making its way into northern Utah toward the end of the day. Showers are expected to spread into the Wasatch Front and northern Utah by Sunday morning, increasing in intensity later in the day. Most of the moisture will be in the form of valley rain and mountain snow.

It’s expected to clear out by the start of the next workweek.

Projected accumulations and cooldown

Precipitation levels aren’t forecast to be anywhere near as strong as what the region has received already this month, but it will snap a brief dry stretch. Most areas will receive 0.10 to 0.33 inches of precipitation, with some places potentially receiving up to a half-inch, according to KSL Weather models. Salt Lake City needs just 0.05 inches of precipitation to reach 5 inches this month for just the fifth time since 1874.

The region’s mountains are projected to receive 2 to 6 inches of snow, with some places possibly receiving more. Johnson said the snow line will likely start near 9,000 feet elevation, before dropping to 6,000 feet toward the end of the system — but there likely won’t be as much precipitation left for snow by that point.

High temperatures along the Wasatch Front and northern Utah will drop from the upper 60s and low 70s on Saturday to low-to-mid 50s on Sunday and Monday, before a warmup later next week.

The storm is forecast to skip most areas south of Nephi, leaving central and southern Utah mostly dry. However, remnants of a system that produced rain in the state last week proved to be fruitful for many southern Utah communities over the last few days.

Escalante received as much as 0.89 inches, while Parowan and Panguitch Lake also ended up with over a half-inch of precipitation. Brian Head Resort reported receiving 5 inches of snow from the 0.8 inches of precipitation it received from the storms.

Clear conditions are forecast for southern Utah this weekend, with highs in the mid-70s closer to St. George lasting into next week.

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