Archived - Not Current !!
Advisory in effect Mar 19 for Highland Peak, CO

Issued on:Sat, Mar 18, 2023 at 4:30 PM

Moderate at all Elevations

You can trigger a large avalanche that breaks on weak layers buried deep in the snowpack. Although a poor snowpack structure can be found on many slopes, the most dangerous slopes face an easterly direction. This is where recent storm snow sits on buried weak layers and crusts. The only way to deal with this avalanche issue is to avoid steep easterly slopes. You may not get any indication of unstable snow before you trigger a large and dangerous avalanche.

Several large avalanches have been triggered over the last few days in the Marble area. Tragically, on Friday, three backcountry tourers were caught in a very large avalanche and one was buried and killed. You can find a preliminary report on our website (click here). Our deepest condolences to the friends and family of the deceased.


Problem 1: Persistent Slab
NW through E all elevations
W and SE near and above treeline
Likelihood: Possible
Size: Large to Very Large

Central Mountains Regional Discussion

An avalanche caught three backcountry tourers southwest of the town of Marble on Friday. Two members of the group were injured and one was completely buried in the avalanche. The person that was buried did not survive. This avalanche released on an east-northeast aspect above treeline. It broke two to three feet deep, 300 to 500 feet wide, and ran 2400 vertical feet. 

Although the danger is MODERATE across the Central Mountains region you can still trigger a large and dangerous avalanche across much of the region. We are dealing with buried persistent weak layers and it will be a while because for these problems get better. The main issue is thin crusts, surrounded by faceted layers, on easterly slopes. These buried crusts are thick at low elevations and on south and southwest-facing slopes, making it hard to affect weak layers, but as you go up in elevation, the crusts are thinner and faceting is more extensive around these thinner crusts. The thinner crusts make it easier for a person to collapse the weak layers beneath the crusts, triggering an avalanche.

As we have seen, the vast majority of recent avalanche activity is on easterly-facing slopes associated with these crust/facet combinations. Observers reported multiple skier-triggered avalanches near Marble on Thursday breaking on this layer and we now add to the tragic accident on Friday to this list. Backcountry riders have also triggered similar avalanches in the Gore Range and near Fremont Pass.

Around Ashcroft and south of Aspen, an avalanche cycle during the first week of March also highlights the danger and destructive power of Persistent Slab avalanches. These avalanches around Ashcroft broke even deeper than the layers mentioned above and are due to a generally weak snowpack. The snowpack around Ashcroft is much more faceted from the ground to the middle of the pack, unlike the deeper areas to the west. But to add insult to injury, you will also have to deal with upper snowpack weak layers in this area too.

The new snow on Wednesday night and Thursday did little to change the danger throughout the Sawatch Range and the Holy Cross and Frying Pan Wildernesses. That being said, in the shallowest areas of this zone, like near Fremont Pass, conditions are a bit more dangerous. The threat of Persistent Slab avalanches still drives the danger in this zone. There are persistent weak layers buried one to three feet deep, and like the rest of the region, easterly-facing slopes are the most dangerous. The shallow and weak nature of the snowpack near Fremont Pass allowed a backcountry traveler to trigger a large slide on an east-facing slope near treeline on Thursday. While other parts of this zone have deeper and stronger snowpacks, the difference is only one to two feet of snow. If you find the "sweet spot" in a thinner area, you can easily trigger a similar avalanche.

Another notable avalanche was near the town of Pitkin. It was observed on Friday by a local resident. They said it was the first time they had seen this slope slide in 10+ years. The snowpack around Pitkin and the southwest Sawatch Range is similar to what we mentioned for Fremont Pass. The snowpack is faceted top to bottom, and with the recent storms, we now have a cohesive slab of snow for the first time in months. This problem will only get worse with the midweek storm and if either of these areas gets over a foot of snow, expect the avalanche danger to quickly rise to HIGH (Level 4 fo 5)

The sun will continue to shine on Sunday and wind speeds will remain light before clouds begin to stream into Colorado ahead of our next atmospheric river event. While temperatures will generally be cool and temperatures will dip into the single digits at night, you should beware of any steep, rocky slope that gets significant warming from the sun during the day. Moist snow can easily shed off of steep southerly-facing slopes with a few hours of consistent warming and no wind to keep surfaces cool. Take care if you travel under any such slopes late in the day. Enjoy the relatively tranquil weather while it's here before unsettled weather returns next week.

Weather

On Sunday (3/19), light northerly flow veers to west as the large Great Lakes low-pressure system moves off to the east. The flattening high pressure ridge over Colorado allows for some warmer air to move in, resulting in a slight bump in max temperatures. Winds increase throughout the day from their current light speeds but it doesn't ever get too windy on Sunday. Clouds move in later ahead of a low-pressure trough that will bring snow on Monday.

Moist southwest flow overtakes the Southern Mountains with snowfall beginning early morning. Snow spreads through the rest of the state during the day though the heaviest snow is confined to the San Juan Mountains, western Elk Mountains, and the Grand Mesa. The highest precipitation rates are in the evening just before the trough axis passes which happens around midnight. Light snow continues Tuesday morning for the south with most areas seeing dry weather prior to the arrival of the next stronger system. Snow totals with this first system for the snowy areas areas are in the 8 to 12 inch range.

The center of a stacked, closed low-pressure system makes landfall on the California coast midday Tuesday. Rounding the base of this system is a strong jet stream that noses into Colorado while tapping into deep, tropical moisture. Snowfall kicks back up around noon Tuesday and intensifies later in the day. The same areas mentioned above, that are favored for the Monday storm, are favored again. This moist and strong system won't leave the less-favored areas high and dry though. Expect 6 to 12 inches in the north, and east of the Continental Divide, while the snowier areas of the south and west-central mountains exceed two feet. Heavy snow continues overnight and into Wednesday morning. Winds are strongest on Wednesday. Thursday brings lighter orographic snow under westerly flow and generally improving conditions.