In Europe, three key factors are evaluated to get the avalanche danger level:

Snowpack Stability: Snowpack stability answers the question, 'How easily can an avalanche be started?' Snowpack stability always varies between different places in the terrain, it is not the same everywhere.
Spatial distribution of the snowpack stability: The spatial distribution answers the question, 'How common are the spots where an avalanche can be triggered?' This is also referred to as the frequency.
Avalanche Size: This factor addresses the question, 'How large can avalanches become?' The potential size of avalanches varies with snow conditions and the scale of the slope. Larger avalanches pose a greater risk. When assessing avalanche danger, it is the largest expected avalanches in the area that are taken into consideration.

You can read more on the European avalanche danger scale on www.avalanches.org.

This is the website of European Avalanche Warning Services, EAWS.