Pattern Change Is Bringing First Snow of the Season to Parts of Rockies This Weekend

Linda Lam
Published: September 16, 2017

A noticeable pattern change is taking shape, especially across the West where the first snow of the season is falling in some locations.

In the West, a dramatic change in the weather is taking place as a strong upper-level low-pressure system has pushed southward into the Plains, spreading much colder temperatures, along with rain and some higher-elevation snow in the northern Rockies.

(MORE: Fall 2017 Temperature Outlook)

This change is courtesy of a shift in the jet stream. Over the West, the jet stream is taking a southward dip in the region, allowing colder conditions to infiltrate farther south. Conversely, the jet stream is being pushed northward over the East, with mild temperatures streaming northward into the Midwest and Northeast.

Upper-level setup for mid-September, with a southward dip in the jet stream over the West and a northward bulge over the East.

As the colder air flows in behind an area of low pressure embedded in the dropping jet stream, rain is changing to snow in the mountains of southwestern Montana, western Wyoming and portions of Idaho.

Current Radar

Snow began falling on Thursday in western Montana, coating surfaces and Butte, Montana began reporting snow very early Friday morning.

At the base of Great Divide ski area near Marysville, Montana reported 24 inches of snow. Frohner Meadow, Montana, part of the SNOTEL network measured 11 inches of snow. Up to 8 inches was reported near Clancy, Montana where numerous tree limbs came down. 

Heavy, wet snow also led to tree damage and power outages near Newcomb, Montana. In addition, heavy snow resulted in the closing of Beartooth Pass at Vista Point on Route 212.

Below we take a closer look at what to expect with this pattern change that may last for a while.

Chilly, Snowy West Forecast

Summer (June-August) was one of the top-five warmest summers on record in much of the West, according to the Southeast Regional Climate Center, and the unusual warmth has persisted into September, so the cold blast will be even more noticeable.

Warmer-than-average temperatures continued through Tuesday but, now, cooler temperatures are pushing south, making it feel more like fall and even winter in some cases.

Many locations saw temperatures drop more than 40 degrees from early this week to Friday. Several locations also set daily records for coldest high temperature on Friday, including Helena, Montana which only reached 40 degrees.

Temperatures will only climb into the 40s and 50s again on Saturday. A few higher elevations may see highs only top out in the 30s from eastern Idaho into western Montana and northwestern Wyoming. Temperatures will begin to moderate on Sunday, before another blast of cold temperatures move in next week.

Forecast Highs

Low temperatures will be even chillier, with temperatures dropping into the 20s and 30s for much of western Montana, eastern Idaho and Wyoming on Sunday morning. Widespread frost is possible and, in some spots, there may even be a hard freeze Sunday morning in low-lying areas. Freeze watches have been issued for parts of Wyoming on Sunday morning.

(MAPS: Weekly Planner)

These below-average temperatures allowed the rain to change to snow in many spots. Significant snow is possible across portions of the higher elevations of western Montana and northern and western Wyoming.

Some of the higher mountain peaks may pick up a few inches of additional snow through Saturday. 

The heavy, wet snow resulted in damage to trees and power lines. In addition, travel was difficult in spots and some passes may be impacted with heavy snow and low visibility, mainly into Saturday afternoon.

This pattern change is also anticipated to assist with slowing the ongoing wildfires in the area.

In addition to being the first significant snowfall for the higher elevations, this system is also bringing the first significant rainfall to many areas since June. Great Falls, Montana recorded just over 2 inches of rainfall from Wednesday evening through Friday. The 1.10 inches that fell on Friday made it the wettest day in almost two years.

Snow in mid-September does happen in the northern Rockies, especially in the higher elevations, so this is not all that unusual.

(MORE: When the First Snow of the Season Typically Falls)

Pikes Peak and Mount Massive in the Colorado Rockies already saw the first snow of the season in early August. Many areas of the West, including Denver, Cheyenne and Billings, have seen snow as early as early September.

However, given the recent warm conditions, campers and hikers need to be prepared for freezing temperatures and snow

Mild East in Mid-September

Meanwhile, parts of the East saw cooler-than-average conditions early this week, due in part to the clouds and rain from the remnants of Hurricane Irma.

Several cities set daily record-cold high temperatures on Monday (new record in parentheses), including: Asheville, North Carolina (60 degrees), Knoxville, Tennessee (62 degrees), Greenville, South Carolina (62 degrees), Huntsville, Alabama (65 degrees), Birmingham, Alabama (66 degrees), Montgomery, Alabama (68 degrees), and Jacksonville, Florida (76 degrees).

High temperatures remained below average in portions of the South and Ohio Valley on Tuesday and Wednesday, where highs were generally in the 60s.

Five-Day Forecast

This weekend, temperatures will return to near average across the South and into the Ohio Valley and mid-Atlantic, with warmer-than-average temperatures prevailing from the Plains into the Midwest and Northeast.

Highs will generally reach into the 80s, while lows in the 50s and 60s can be expected. The southern Plains will see highs top out in the 90s.

It will also feel more humid for much of the South and East late this week.

(MAPS: 10-Day Forecast)

These more summer-like conditions are expected to last at least into the weekend across the East and likely into next week.

Early next week, a cold front is expected to push eastward bringing a chance for showers and thunderstorms.

In addition, portions of the East Coast from the mid-Atlantic into the Northeast will need to watch Jose for potential impacts next week.

(MORE: Jose Forecast)

MORE: First Snowfall of the Season (PHOTOS)

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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