Winter and Summer are clashing in a pretty typical Spring fashion Monday. The day starts warm and then turns stormy with a healthy amount of wind expected. Be sure your travel plans account for a wide variety of changing conditions.
Weather Forecast
There is a lot of uncertainty in the current weather forecast as winter and summer battle it out in this season we call spring. In short, temperatures are expected to cool a bit Monday and Tuesday and the Cariboos should see a bit of precipitation before the ridge rebounds and sends the freezing level into the heavens once again. MONDAY: Freezing level beginning near 2000 m, lowering throughout the day to around 1500 m by sunset, 4 to 8 mm of precipitation expected, overcast sky, moderate winds first out of the southwest switching to northwest in the afternoon. TUESDAY: Freezing level beginning near 1500 m rising to around 1800 m, overcast sky, convective snow/rain showers possible, light to moderate west/southwest wind. WEDNESDAY: Freezing level starting around 2000 m, rising to over 2500 m throughout the day, no significant precipitation expected, strong to extreme west wind, sky steadily clearing throughout the day. For more detailed mountain weather information visit avalanche.ca/weather
Avalanche Summary
Over the last week the very warm temperatures have initiated a lot of avalanche activity. As recently as Friday size 2.5 isothermal slab avalanches were reported from all aspects including north. Earlier in the week avalanches to size 3 were failing on the late February crust. Loose wet avalanches to size 2.5 were reported from all aspects/elevations except for high elevation north over the last few days. Cornice failure has also been rampant triggering avalanches up to size 3.
Snowpack Summary
The warm daytime temperatures and weak/non-existent overnight refreeze over the past few days have moistened the upper snowpack at all elevations. High elevation north may be the last hideout of relatively "cold" snow heading into Monday morning. Below 1400 m, the snowpack is likely fully isothermal. The March 20th rain crust is present to around 2000 m, but the warm temps have likely allowed the overlying 30 to 50 cm of snow to bond well. Once it freezes, March 20th should not be much of a concern. The late February persistent weak layer is now down 80 to 160 cm below the surface. While it may be a concern in isolated terrain, it would probably take a large trigger like a cornice fall or surface avalanche in motion to provoke it.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
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.