- Date
- Tuesday, April 18, 2017
Your guide to spring conditions, when things stay frozen day and night
Weather: After a few days of warming due to increased air temperatures, solar radiation, or in some cases rain, subsequent cooling patterns can lead to surfaces refreezing for days on end. This cooling pattern typically falls under a north or northwesterly upper flow, and is generally characterized by below-freezing temperatures and overcast skies.
Snowpack: Previously moist or wet snow that has refrozen with cooler temperatures generates a strong, supportive crust (usually at least 10cm thick) essentially “locking” the snowpack in place.
Exceptions to this may be high north-facing terrain where a wintery snowpack may still prevail, or low elevation slopes where above freezing temperatures may be keeping surfaces moist or wet.
In this scenario, deep persistent weaknesses such as the February 10th facet layer or basal facets which formed early season would be highly unlikely to trigger. These weaknesses would require a very large input (cornice, explosives) on an unsupported slope with the potential for thin spot triggering.
Avalanche Activity: In this scenario the risk of dangerous avalanche activity is reduced. Exceptions may include lingering winter-like instabilities on high, north facing slopes, or avalanches related to warmer temperatures at the lower end of treeline. Localized loose wet avalanches are still possible during sunny breaks, but their size and intensity are likely to be lower.
Terrain and Travel Advice:
- This is the time to consider bigger objectives bearing in mind that deep instabilities are still present in isolated terrain.
- Remember that conditions can deteriorate in hours, or even minutes, if the sun comes out or if it starts to rain. If this happens, be prepared to back off onto more simple terrain.