Snow in Jackson Hole, Wyo. (Jackson Hole via Instagram)

On Monday, an unusually intense cold front — which forecasters described as “exceptional” — swept through the northern Rockies. The front set the stage for a rare July snow event that deposited up to several inches at above 8,000 feet elevations in Montana, Wyoming and Idaho.

“This pattern should not happen in July,” commented the National Weather Service (NWS) forecast office in Billings, which is bracing for its “windiest July day ever” in the front’s wake.

After the blast of cold air arrived Monday, snow was reported at Glacier National Park (8,000 feet elevation) in Montana, as well as the Big Sky (Mont.) and Jackson Hole (Wyo.) ski areas.

“In my 27 years as the chief meteorologist for KXLF/KBZK, I have only reported a few times that snow is falling in SW Montana in July,” said Mike Heard, a television meteorologist for the affiliate serving Bozeman and southwest Montana. “Today [Monday] is one of those days.”

Here’s another eyewitness report from Monday, via the Great Falls Tribune:

“This morning it was snowing right where the ski lifts start and all the way up the mountain,” said Tom Conway, assistant golf pro at Big Sky Resort south of Bozeman. “At our elevation on the golf course, about 6,500 feet, it was raining. But at 9,000 feet there was about an inch or two of accumulation.”

“I’ve been here for four summers,” Conway added, “and this is the first time I’ve seen it snow in July. It was a pretty crazy day.”

The snow and cold were surely a shock, as the same areas were awash in mid-summer warmth over the weekend.

In Missoula, afternoon temperatures were only in the upper 40s Monday after they had been in the upper 80s on Saturday.

Objective measures of the cold front’s strength compared to past events led the NWS forecast office in Billings to conclude it was “exceptional”:

It left behind a deep pool of cold air at high altitudes (or jet stream trough) that allowed the snow to occur.


GFS model simulation of high altitude weather pattern Monday evening (WeatherBell.com)

As the front blew through, it also triggered severe thunderstorms, including a possible tornado that destroyed seven camper trailers in the Bighorn mountains, according to the NWS forecast office in Riverton, Wyo.

Although this particular snow event produced more snow in more areas than normal, very light amounts of snow are not uncommon at very high elevations in parts of the northern Rockies in July. Montana has at least one reporting station, Mystic Lake (elevation of almost 8,000 feet) in the southern part of the state, that averages 0.1 inches snow in July.

After an extremely windy day today, particularly in the northeastern Montana, much milder and more tranquil conditions are forecast to return to the northern Rockies by the middle and later portions of the week.


Wind visualization Tuesday morning (hint.fm/wind/)

Below is a collection of Montana, Wyoming and Idaho snow photos from social media …

Photos from Big Sky Resort in Montana.

Photos and video from Jackson Hole, Wyo.

TODAY it's #snowing in #Jacksonhole. Wait, it's July 27th. Photo from tram operator @peterlandsman. #jhdreaming #winteriscoming

A photo posted by Jackson Hole Mountain Resort (@jacksonhole) on

#winteriscoming. July 27th and it's #snowing in #Jacksonhole.

A photo posted by Jackson Hole Mountain Resort (@jacksonhole) on

Additional snow photos from the northern Rockies

https://twitter.com/Bryce_Koontz/status/626027790404448257

Correction, Friday, July 31: This post originally stated Missoula recorded a trace of snow on Monday based on a report from the National Weather Service. That was an error. Although hail fell in Missoula on Monday, July 27, no snow fell.