Bollettino valanghe

Provo

Pubblicato il Jan 4, 2022valido fino al Jan 5, 2022Utah Avalanche Center

Pericolo valanghe

Alta quota
Limite del bosco
Sotto il limite del bosco

Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The avalanche danger is CONSIDERABLE on mid and upper elevation slopes facing west through north and east. Avalanches may break down 4-6' deep (possibly deeper) and hundreds of feet wide. Natural avalanches are possible, and human-triggered avalanches are likely. Avoid this terrain because those avalanches will kill you. Watch for and avoid any freshly formed wind drifts on slopes facing southwest, south, and southeast which have a MODERATE avalanche danger at mid and upper elevations.

Pay attention to changing weather patterns. As this next storm system develops, it will bring new snowfall, warm temperatures, and high winds, with that the avalanche danger will rapidly rise.

Problemi valanghivi

Persistent Slabs
N
NE
E
SE
S
SW
W
NW
Alta quota
Limite del bosco
Sotto il limite del bosco
Probabilità
Likely
Dimensione
4
The situation is very simple - there is a persistent weak layer (PWL) of old, faceted snow near the ground with 3-10 feet of snow on top of it. This layer has been fracturing and producing large and destructive avalanches. Winds increased from the south and have likely been loading the slopes where this PWL exists. The likelihood of triggering these massive avalanches has gone down just a little in recent days, but the size and destructive potential of these slides hasn't changed.

This layer exists on west, north, and east-facing slopes where old snow lingered and weakened in November and was buried by December snowfall. It doesn't exist on south-facing slopes because it melted away in November, and December snowfall landed on bare ground on those slopes.

Over the last week, snowfall containing up to 8 inches of water has been added to the snowpack. We focus on water amounts because that tells us how much weight is added to the snowpack. For a slope the size of a football field, snow with 8 inches of water weighs 2,800,000 pounds. Imagine that amount of snow crashing downhill.

Video from the Firewater Avalanche off of Little Water Peak in Big Cottonwood Canyon, of the central Wasatch.

How will we know when this avalanche problem heals? That's a tough question to answer, and we mainly have to let the snowpack answer it. For now, avalanches are still happening and that's all I need to know. As we look into the future, it will heal, but I can't tell you when. We will be monitoring the snowpack and avalanche activity and keep you updated.
Wind Slabs
N
NE
E
SE
S
SW
W
NW
Alta quota
Limite del bosco
Sotto il limite del bosco
Probabilità
Likely
Dimensione
3
Since yesterday, the southwest winds have increased drastically and have likely been transporting snow. For the snowpack, when the winds drift snow, it's the same as if snow is falling out of the sky. The snowpack doesn't care where the snow comes from, it feels the added weight. So, on northerly facing slopes, these winds have added snow and weight, and stress to the avalanche problem listed above.

While these south winds have mostly formed drifts on northerly facing slopes, they can load any slope at mid and upper elevations because winds swirl and change direction as they pass through the mountains.

What to do? Avoid any steep west, north, or east-facing terrain that has the avalanche problem listed above. If riding south-facing avalanche terrain, look for evidence of fresh drifts and wind slabs that look wavy, rounded, smooth, and pillowy and avoid them as well. Fortunately, those fresh drifts are easy to see and go around.

Recent Activity

One new report of an avalanche in the Provo area backcountry. While boot packing below Woolly hole, two skiers released a 12-15” deep wind slab that broke 50-60’ above us and about 50’ wide. It only ran 100-200’ before stopping and neither of the skiers were carried. The terrain was north-facing just shy of 9,000 feet, 40-45 degrees. Ski resorts and DOT continue to get results with explosives in upper elevation NW-N-E facing terrain.

View all the recent avalanche activity HERE.

Photo of the 12-15" deep wind slab that was released on a north-facing slope near 9,000' of Wooley Hole. (Coyne & Gill)

Snow and Weather

Temperatures this morning are in the upper 20s to low 30s F. Overnight, southwesterly winds increased drastically and will continue to increase into the morning. At mid-elevation bands, they are blowing 20-30 mph gusting 50 mph.

Today temperatures will generally rise to the mid-30s F. Clouds will continue increasing into the morning, bringing light snowfall and high winds. Snowfall rates should remain less than one inch an hour today, with peak snowfall rates between the late morning and early afternoon. We can expect 2-5" of new snow by dinner. Winds will continue to increase throughout the morning and transition more westerly. Winds will blow 20-30 mph, with gusts up to 35 mph at mid-elevations. At upper elevations, gusts may reach up to 60 mph.

While we get a bit of snow today, it will taper off this evening and the heavier snowfall arrives Wednesday morning to Thursday morning. This storm looks like it will have strong winds, increasing temperatures, and increasing snow densities.

Warm temps and a few days of intermittent sunshine have warmed the snow on south-facing slopes and most will have a slight crust this morning. Coverage is fantastic, and settled snow depths, even at lower elevations are 3-4 feet. Upper elevation areas and the upper cottonwoods have snow depths up to 6-7 feet.

General Announcements

Who's up for some free avalanche training? Get a refresher, become better prepared for an upcoming avalanche class, or just boost your skills. Go to https://learn.kbyg.org/ and scroll down to Step 2 for a series of interactive online avalanche courses produced by the UAC.

CLICK HERE FOR MORE GENERAL INFO AND FAQ

This information does not apply to developed ski areas or highways where avalanche control is normally done. This forecast is from the U.S.D.A. Forest Service, which is solely responsible for its content. This forecast describes general avalanche conditions and local variations always occur.

Observations and Avalanches

Backcountry Emergency Procedures