Here’s how ‘Pineapple Express’ is expected to impact Utah over next week

SALT LAKE CITY — This week has produced spring-like temperatures, but a reminder Utah is still in the middle of winter is on the horizon.

The National Weather Service issued a mix of winter storm warnings and winter weather advisories for the mountain regions across the state, where upwards of 1½ to 2 feet of snow is possible between Thursday and Saturday afternoon.

The water-heavy storm is forecast to produce mostly rain in the valleys with heavier totals in southern Utah, but there could be a chance for some valley snow in northern Utah at times, said KSL meteorologist Matt Johnson.

The incoming storm is the first of a “two-punch” system that, he said, is expected to produce even more mountain snow early next week.

All aboard the ‘Pineapple Express’

Utah’s forecast is dominated by remnants of low-pressure systems forecast to slam California, referred to as a “Pineapple Express.” These are when moisture builds up in the Pacific Ocean near Hawaii and produces atmospheric rivers that produce “heavy rainfall and snow” to the Western parts of the U.S. and Canada, as noted by the National Oceanic and Atmospheric Administration.

In this case, a storm off the Pacific Northwest is dumping massive precipitation in California, Oregon and Washington. The National Weather Service has various weather advisories in place for those states, where some parts may receive multiple inches of rain, elevating flood risks in some areas.

Utah won’t receive as much precipitation, but it could still get some moisture as the storm moves east.

“When we get leftovers from decaying atmospheric rivers, we can still get good (precipitation) in the mountains and it does look like both of these atmospheric river events will hit a bull’s-eye in southern Utah,” Johnson said. “That’s really where our snowpack has been suffering this year … so this is great news for southern Utah.”

The storm is forecast to arrive in southern Utah on Thursday morning before spreading to other parts of the state as the day continues. Johnson said southern Utah is forecast to receive the most precipitation throughout the day with more scattered showers forecast in northern Utah.

More widespread rain and snow are forecast throughout most of Friday, favoring the northern half of the state later in the day. He said there’s a possibility of a rain-snow mix or snow, at times, across the Wasatch Front in the evening and early Saturday.

Some precipitation is possible on Sunday, but the brunt of a second storm is expected to arrive in southern Utah on Monday night and northern Utah on Tuesday, bringing more valley rain and mountain snow.

Snow and rain accumulations

The National Weather Service’s warnings and advisories only cover the first storm. It warns the mountains in southern Utah are forecast to receive 1 to 2 feet of snow between Thursday and Saturday morning. The highest totals are expected near Brian Head,

The agency’s Salt Lake City office issued a handful of winter weather advisories for other parts of the state that last into the late afternoon on Saturday. Those alerts, which could be elevated into warnings as the storm arrives, state that:

• 10 to 18 inches of snow is forecast to fall in the Wasatch Mountains, with the highest totals in the Upper Cottonwood Canyons and mountains near Logan.
• 6 to 12 inches of snow is forecast for the West Uinta and Wasatch Plateau/Book Cliffs ranges, while the central mountains could receive up to 14 inches in some spots.
• 3 to 7 inches of snow is forecast for the Upper Sevier River Valley and Bryce Canyon Country areas.

Its Grand Junction office issued a winter storm watch for La Sal and Abajo mountains, which may receive 10 to 20 inches of snow. Drivers are urged to slow down and use caution along mountain passes across all of the alert areas.

Johnson said most weather models indicate the storm will provide more valley rain than any snow based on the projected snow line. It will depend on later cold air that mixes into the storm, leading to any major valley accumulations.

Weather models indicate the storm has the potential to deliver 0.25 to 1 inch by the time it clears up. The heaviest valley rain totals are forecast for areas near St. George.

That’s all before the second round is forecast to arrive next week.

Snowpack boost

Meanwhile, both rounds of snow are expected to pad Utah’s snowpack after a strong January. Utah’s statewide snowpack average remains at 96% of the median average for the end of the month after entering at 69%.

FEAST OR FAMINE: January has produced for some and not so much for others across the state.

Our next storm moves in tomorrow and will impact southern Utah first. We're talking details on @KSL5TV right now. #utwx pic.twitter.com/NoknIG9es4

— Matthew Johnson (@KSL_Matt) January 31, 2024

That said, it’s only a little past halfway to the median average peak with about two months left before the average peak date. Since Pineapple Express remnants typically produce more water-heavy snow, the season total could receive a decent jolt over the next seven days as the storms arrive.

“This is great for drinking water and reservoir water supply in the summer,” Johnson said.

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