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.
Stellar crystals are less prone to slab formation.
Check hardness of snow layers with hand and fingers. Planning - Choose safe routes. Ridges and wide valleys are safer. Travel across likely avalanche areas one at a time to a safety zone such as rock outcrops or dense trees. Swim to stay on top of the snow.