Lucky for us, most storms deposit new snow with denser snow
on the bottom and lighter snow on top—just the way we
like it. This is because most snow comes from cold fonts, which
usually start out warm and windy but end up cold and calm. But
sometimes snowstorms deposit denser, stiffer snow on top of
softer, fluffier snow. We call this “upside down”
snow. We often call it “slabby” or “punchy”
meaning that you punch through the surface slab into the softer
snow below, making for difficult riding and trail breaking conditions.
It also means that we need to carefully monitor avalanche conditions
within the new snow because—by definition—a denser
slab has been recently deposited on top of a weaker layer, which
should make anyone’s avalanche antennae stand at attention.
Most instabilities within upside-down snow stabilize within
a day or two.
The kind of weather conditions that often produce upside-down
snow include warm fronts, storms in which the wind blows harder
at the end of the storm than the beginning, or storms that end
with an unstable airmass, which can precipitate a lot of graupel
within instability showers.