May Snowstorm: Feet of Snow in Wyoming, Colorado Mountains; Denver's Latest-in-Season Snow Event in 42 Years Ahead

Jon Erdman
Published: May 18,2017

An unusually strong, damaging late-spring snowstorm is kicking into high gear in the Rockies, bringing feet of snow to some higher elevations, and likely bringing the latest-in-season snow event to Denver in over 40 years.
(MORE: Winter Storm Central)
Winter storm warnings and advisories are in effect throughout Wyoming and the mountains of Colorado. These warnings include the cities of Cheyenne and Laramie, Wyoming.
Winter storm watches continue in effect for most of the Front Range Urban Corridor of northern Colorado, including the Denver metro area, Boulder and Ft. Collins.

Winter Weather Alerts

Happening Now

The majority of snow is now falling over parts of Wyoming and the high country of Colorado, with wrap-around snow still occurring as far west as the mountains of northeast Nevada.
Snow levels are falling, with snow reported at Rawlins, Wyoming (6814 feet), Laramie, Wyoming (7,284 feet), Cheyenne, Wyoming (6,116 feet) and Boulder, Colorado (5,289 feet). A stretch of Interstate 80 has been closed in Wyoming between Laramie and Cheyenne, according to the Wyoming DOT. U.S. 287 south of Laramie has also been shut down to the Wyoming/Colorado border.
Heavy snow was reported at the summit of Colorado's Berthoud Pass Thursday morning, with lightning visible in the distance.
For now, a chilly rain is the most dominant precipitation type along the Front Range of Colorado, but some wet snow flakes have been mixing in, already, at times, in the Denver metro area.

Current Radar, Satellite, Temperatures, Conditions

The top snow total so far from this storm is 31 inches near Nye, Montana, which is located in a mountainous area in the south-central portion of the state.
An estimated 9 inches of snow in Bear Canyon near Bozeman, Montana, snapped numerous tree limbs and triggered power outages late Wednesday night, according to the National Weather Service.
Here are a few selected snowfall totals through Thursday morning, local time.

• Idaho: 11.0 inches near Pierce; 9.0 inches near the Red River Hot Springs
• Montana: 31 inches near Nye; 6 inches in Bozeman; 4.5 inches in east Missoula
• Utah: 7.2 inches at Alta; 5.0 inches near Smithfield; 0.3 inches in downtown Salt Lake City
• Wyoming: 17.0 inches at Teton Pass (8,200 feet); 4-5 inches in Rawlins
• Colorado: 15 inches in Nederland; 11.5 inches near Breckenridge

While some low-elevation locations will remain too warm for accumulating snow – it is mid-May, after all – other high-mountain valleys and plateaus, and parts of the Interstate 25 corridor, including Denver and Cheyenne, Wyoming, will see accumulations.

Timing

Thursday

• Heavy snow is expected in the higher elevations of Wyoming and high country of northern Colorado.
• Some wet snow is also possible in some lower elevations of Wyoming and northern Colorado.
• Snow will taper off in the mountains of Idaho, Montana, Utah, and Nevada.
• Precipitation along Colorado's Front Range corridor should remain rain during the day, but is expected to change to wet snow overnight Thursday night.

(FORECAST: Cheyenne, Wyoming | Laramie, Wyoming)

Thursday's Forecast

Friday

• Wet snow, possibly heavy in spots, continues in southern and eastern Wyoming and Colorado.
• The snow should taper off in most areas during the evening hours. 

(FORECAST: Cheyenne, Wyoming | Denver, Colorado)

Friday's Forecast

Snowstorm Impacts

• Over a foot of snow is likely in the mountains of Wyoming and northern Colorado.
• Some locations in the Snowy Range and Medicine Bow Mountains of southeast Wyoming and mountains of northern Colorado may pick up over 2 feet of snow.
• The I-25 Front Range corridor in northern Colorado, including the Denver metro area could see several inches of accumulation Thursday night and Friday, particularly over the city's south and west sides. 
• Heavier totals are likely over the foothills west of the I-25 corridor.
• Heavier totals are also likely in some lower elevation locations of Wyoming, including Cheyenne and Laramie.
• The heavy, wet snow accumulations combined with increasing winds could damage tree limbs and cause power outages, particularly in southeast Wyoming and northern Colorado (including the Front Range urban corridor).
• Road closures are likely in Wyoming, including Interstate 80 between Laramie and Cheyenne and possibly Interstate 25 in southeast Wyoming.
• Travel into Colorado's High County on Interstate 70 west of Denver and over the Palmer Divide between Denver and Colorado Springs may become slippery/hazardous by Thursday night or Friday morning.

Snowfall Forecast Through Friday

How Unusual is This So Late in Spring?

May, even June snowfall in the highest elevations of the Rockies is not unusual.
Accumulating snowfall beyond the middle of May in the Mile-High City, however, is rare, but not unprecedented.
This is only the 4th time a winter alert has been issued for Denver in May since 2006.
According to weather records maintained by the National Weather Service office in Boulder, there have been only five snow events on record producing more than 1 inch of snow in Denver after May 17. The last time it happened was in 1975. Broncos legend John Elway was only 14 years old.
Denver has seen accumulating snow as late as June 5 (1953) and a trace of snow as late as June 12 (1947).
Storms this late in the year have more potential to be more dangerous due to the greening of trees.
Possibly their worst late-May snowstorm dumped 10.7 inches of snow at Stapleton Airport from May 25-26, 1950.
Accompanied by wind gusts up to 30 mph, this pre-Memorial Day weekend storm caused extensive damage to utility wires and trees which were in full leaf. 
Cheyenne, Wyoming, last saw a 6-inch-plus snow event this late in spring about 67 years ago, when Harry Truman was President.
Incredibly, Wyoming's capital city has seen three such June events in their history, dating to the late 1800s.
Salt Lake City recorded their first measurable May snowfall in seven years, despite being only 0.1 inch.
Logan, Utah, picked up more than 4 inches of snow by Wednesday morning, only the second time in history dating to 1893 they've had such a heavy snowfall so late in the spring.

Storm Recap, So Far

The weight of wet snow already triggered power outages and downed trees in the city of Missoula. Missoula has received 2.7 inches of snow so far – a daily record for May 17.
Portions of I-90 in the Homestake Pass east of Butte, Montana were blocked for a few hours in both directions Wednesday afternoon due to jackknifed semis. Conditions were reportedly snowy and icy at the time of the crashes.

Piling on the Rockies Snowpack

Despite recent warmth, there is still plenty of snow left to melt in the mountain West.

Basin-wide estimated snow water content as a percent of average on May 12, 2017. Areas shaded in dark blue were at least 150 percent of average snow water content.

The Natural Resources Conservation Service's SNOTEL network estimated water content in the snowpack on Friday was an incredible 641 percent of average in parts California's Sierra and over 150 percent of the average for the date in parts of Wyoming, Idaho, Utah, northern New Mexico, western Nevada, Oregon and southern Washington.
In fact, a half-dozen locations from the Sierra to Wyoming have a record-high snow-water content for this time of year in 30 to 40 years of records, according to the SNOTEL network.
Northern California's Lassen Volcanic National Park recorded their second largest snowpack on record, beaten only by the 1982-83 season.
Several locations in Wyoming have had a record-wet October through April in 2016-17. As a result, spring flood potential is either moderate or high in river basins that charge with snowmelt in western Wyoming, according to the National Weather Service (NWS).
In Utah, releases from Deer Creek Dam were expected to trigger flooding on the Provo River.
Mandatory evacuations were expanded Thursday for additional homes in Hailey, Idaho, due to flooding of the Big Wood River, which was expected to remain in flood stage for a prolonged period due to the remaining snowpack. According to the NWS, this flooding could persist for several weeks.
While some roads in Yosemite National Park have been cleared, the snow-clearing effort of higher paved roads continues in other national parks. So this fresh snow won't just add to the snowpack – it'll also worsen snowmelt flooding in the weeks ahead.
Jonathan Erdman is a senior meteorologist at weather.com and has been an incurable weather geek since a tornado narrowly missed his childhood home in Wisconsin at age 7. Follow him on Facebook and Twitter.
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