Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 19th, 2019–Dec 20th, 2019

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Purcells.

An intense winter storm is delivering heavy snowfall and strong winds over much of the region. Widespread avalanche activity is expected. Avoid avalanche terrain.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system. Forecast snowfall amounts are uncertain.

Weather Forecast

THURSDAY NIGHT - Snow, 15-30 cm / southwest wind, 30-60 km/h / alpine low temperature near -7

FRIDAY - Snow, heavy at times, 20-40 cm / southwest wind, 40-80 km/h / alpine high temperature near -2 / freezing level 1500 m

SATURDAY - Snow, heavy at times, 15-25 cm / southwest wind, 40-80 km/h / alpine high temperature near -2 / freezing level 1600 m

SUNDAY - Cloudy with sunny periods and isolated flurries / southeast wind, 10-20km/h / alpine high temperature near -8

Avalanche Summary

Significant snowfall amounts, warm temperatures and strong to extreme winds will mean that a natrual avalanche cycle is almost certain for most of the Purcells on Friday.

On Sunday there was a report of a size 3 explosive controlled deep persistent slab avalanche on a north aspect in the alpine. The fracture was 150 cm deep. On Monday there were also reports of a few explosives controlled size 1.5 deep persistent slab avalanches on north aspects at treeline.

Snowpack Summary

An intense winter storm is underway over most of the Purcell region, with anywhere from 15-30 cm overnight Thursday, and another 20-40 cm possible over much of the region throughout the day on Friday. The most significant snowfall amounts are expected further south in the region, with areas near Golden receiving lower amounts.

Anywhere from 40-100 cm of recent snow may sit on a weak layer of surface hoar in sheltered areas at treeline. A second layer of surface hoar primarily found in the in north of the region is found 60-90 cm below the surface in sheltered areas at treeline. There are a variety of crusts buried in the mid to lower snowpack. These crusts have mostly broken down. The base of the snowpack generally consists of facets and depth hoar.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.