Temperatures in Boise are about to take a chilly turn, with temperatures set to dip into the 40s on Wednesday for the first time since May 12. It could get so cold in parts of Idaho this week that some areas of the Boise Mountains, as well as other ranges, see several inches of snow.
The quick dip in temperature is courtesy of a low-pressure system that formed over British Columbia, according to National Weather Service meteorologist Joel Tannenholz.
The system is on a southward trajectory through Washington and Oregon before shifting eastward through Idaho. A cold front will accompany the system, dropping temperatures to the mid-40s on Thursday morning.
Daytime temperatures won’t be as cool, but they’ll stall in the mid-60s through the back half of the week, before warming back up next week — the first week of autumn.
“It’s already moving into the Idaho Panhandle, but there’s not going to be a really dramatic change in temperature when it goes through; it’s more of a gradual cool-down,” Tannenholz told the Idaho Statesman on Tuesday. “This afternoon, the high temperatures are 5 degrees cooler than yesterday.”
While the cooler temps may shock the system, it also might seem long overdue. Through Sept. 17, Boise experienced its sixth-hottest September on record, with an average temperature of 72.7 degrees.
September 2023 so far has been one of the warmest (6th warmest) on record for #Boise with an average monthly temp of 72.7 degrees (as of 9/17).
However, fall like weather is expected Wed. and Thurs. for below normal temperatures. #idwx #orwx pic.twitter.com/R6CH1s8glr
— NWS Boise (@NWSBoise) September 18, 2023
Rain and snow
It’s not just cooler weather that the low-pressure system will bring. As it wraps around the southern edge of Idaho, rain showers will move through the Treasure and Magic valleys and into the central mountains.
Boise’s highest chance of rain arrives Thursday night, at 40%. That falls to 30% by Friday morning.
In Idaho’s higher elevations, that precipitation will bring snow. At least a dusting is possible at elevations higher than 7,000 feet by Wednesday, according to Tannenholz, and that will creep down to 6,500 feet by Wednesday night.
For reference, Stanley is situated at 6,250 feet above sea level, so hiking trails surrounding the popular tourist town could be above the snow line. Stanley will see lows in the 20s this week, while places such as McCall and Ketchum will hit freezing.
As for snow, “maybe 2 to 3 inches up there in the west-central mountains and the higher peaks in the Boise Mountains, east of Idaho City,” Tannenholz said.
Warming back up in Boise?
Sweaters and jackets will come out this week in Idaho’s capital city, but don’t put those summer clothes away just yet. Temperatures will be in the 70s on the weekend and climb back to 79 degrees by Monday, according to the National Weather Service.
The Climate Prediction Center also predicts a 33-40% chance of above-average temperatures over the next 14 days; the average high temperature in Boise in late September is 75 to 77.