Weather is always changing. Differing layers are formed in the snow pack that can be identified as strong or weak layers. Layers of frost hoar can be found in layers of large elongated crystallization. These layers of hoar are often unstable because of their lack of bonding to surrounding layers of snow pack. Wamphy snow is an obvious sign of unsettled snow.
Instability is always highest during or immediately after a storm.
Surface hoar, once covered, creates a nearly indistinguishable weak layer. Depth hoar is a layer of large temperature gradient grains with distinct faces and corners, usually found at ground level. The probability of deep slab instability is many times greater on slopes that have depth hoar than on those without. Extreme instability can be expected when the cold snow surface is a cold crust and the first few centimeters of new snow consists of very cold, cohesionless grains. Rimed spatial dandrites, needles and columns, are especially prone to slab formation.