I'll admit, it's not much, but SNOW is heading to the mountains early Friday morning. A dusting of snow is most likely for peaks above 13,000 feet, in areas like the Collegiate peaks and the Sawatch Range, the Elk Mountains, and the Longs Peak - Rocky Mountain National Park areas. There will perhaps be some wet flakes falling as low as 11,000 feet with no accumulation.
Now that your heart rate has decreased after reading the headline... The associated cold front to this system will mostly bring rain, from Montana to Utah and western Colorado. A flash flood watch has been issued for western Colorado.
KNOW BEFORE YOU GO: A flash flood watch has been issued for western Colorado, including Glenwood Canyon on I-70. If the canyon is under a warning, CDOT will close I-70 there. #COwx pic.twitter.com/vE0zWhZVVf— Alex O'Brien (@WXAlexOBrien) August 18, 2021
Unfortunately, this storm will stay too far north for southern Colorado to feel a significant change. But, a cooldown of about 10 degrees is expected between Wednesday and Friday with increasing clouds.
This first sniff of the season's change comes from a dip in the polar jet stream into the northern Rockies.
As a general rule of thumb, the polar jet stays closer to the Arctic circle in the summer and will migrate south to the mid-latitudes in the winter. The jet stream is on the move between these positions during our transitional seasons of fall and spring.
Waves in the jet stream bring daily and weekly variability with high and low-pressure systems.
This week's storm in the northern Rockies marks the slow transition of the polar jet as it moves south for winter.