Boise has kind of done Dry January, but that could be changing. Here’s what to expect

It’s been a somewhat warm and dry January in Boise, with the city averaging a high temperature of 4 degrees above normal, while precipitation is half an inch below normal.

The city has received just 3.2 inches of snowfall — more than an inch below average — and 3.1 of that came on Jan. 19.

But the trend is about to change, according to meteorologists.

Weekend forecast

Some brief snow showers will move into the Treasure Valley the next two days, but any storms won’t drop significant amounts, with Boise forecast to get a half-inch at most. Bogus Basin is expected to get 3.8 inches and McCall upward of 5 inches.

What will arrive after that is a blast of cold air the state hasn’t yet encountered in 2023. Temperatures will drop in Boise to as low as 4 degrees by early Tuesday morning, and high temperatures won’t be above freezing until later in the week.

Areas of western Montana will see Arctic air plunge into the state, dropping temperatures below 0 there. But Wasyl Hewko, a meteorologist with the National Weather Service in Boise, thinks the cold temps that will reach the Treasure Valley would be better defined as Canadian air.

“If it’s a form of Arctic (air), it’s definitely modified, but it’s definitely colder,” Hewko said. “That typically happens with our northern flow.”

Hewko also noted that the mountains north of Boise protect the state’s southern half from the full blast of cold air.

Why is it getting much colder?

An active Pacific jet stream was drawing subtropical moisture — typically warmer and more humid — from the south for much of the month, according to previous Statesman reporting.

But a high-pressure system over the West Coast is now cutting off the subtropical moisture, Hewko said. The system has also altered the path of the atmospheric river — narrow regions of water vapor — resulting in the U.S. Northwest receiving it from southern Alaska rather than the Hawaii area.

The two changes are setting Boise up for a colder and wetter February.

The Climate Prediction Center’s three- to four-week outlook gives Boise a 50-55% chance of below-normal temperatures and a 55-70% chance of above-normal precipitation.

The historical average temperature for Boise in February is 37.5 degrees and the average precipitation is just an inch, which equates to about 3.3 inches of snow.