Spring snow: wet slides, timing, and the shrinking window

Spring is, for many tourers, the best season: long days, stable weather patterns, and corn snow that skis beautifully. It also has an avalanche problem that behaves nothing like winter's, and people who apply winter habits get caught.

The melt-freeze cycle

Spring snowpacks are dominated by daily cycling. Overnight, clear skies allow the surface to radiate heat and refreeze hard. Through the morning, sun and warm air melt the surface progressively downward. By afternoon, meltwater has percolated into the pack, weakening bonds between grains.

A good overnight freeze produces a firm, supportive surface in the morning that softens into perfect corn snow for a few hours. That window — after the surface has softened enough to ski and before it has degraded into deep slush — is what spring skiing is chasing, and it is measured in hours.

Wet loose avalanches

Point-release slides that start at a single spot and fan out downhill, entraining wet snow. Usually small, and dangerous mainly for what they carry you into — a wet loose slide over a cliff or into a gully is serious.

They are the earliest warning sign of the day. Rollerballs — small snowballs rolling down a slope — and pinwheels mean the surface has lost cohesion and wet activity is starting. This is a direct, visible instruction to move to a shadier aspect or to go down.

Wet slab avalanches

Much more serious and much harder to predict. These occur when meltwater percolates through to a buried weak layer or a crust and lubricates it, releasing a large slab of heavy, wet snow.

Wet slabs are dense — far heavier than dry snow — and they set like concrete when they stop. Burial in wet debris is very difficult to survive and extremely difficult to dig out.

They are notoriously hard to forecast, and forecasters are often explicit about that uncertainty. The high-risk situations are recognisable: the first significant warm spell of spring, the first rain on snow, a night with no refreeze, and any period when water is reaching layers it has not previously reached.

The overnight freeze is the whole thing

Check it before you go, and check it on the ground.

A good freeze needs clear skies — cloud cover traps radiated heat and prevents refreezing — and air temperatures below freezing for a decent portion of the night.

A poor freeze, or none at all, means the snowpack starts the day already wet and weak. On those days, the correct decision is often to not go into avalanche terrain at all, because there is no safe window: the pack never regains strength.

On the ground, the test is simple. Boots and skis should not penetrate a firm crust in the morning. If you are punching through at dawn, that is the answer.

The timing discipline

Start extremely early. Genuinely early — the classic spring start is before dawn, and the aim is to be on the summit shortly after sunrise and descending as the surface softens.

Be off steep, sun-exposed terrain by mid-morning to late morning depending on aspect and conditions. East-facing slopes get sun first and deteriorate first; south faces get the strongest sun; west faces hold until afternoon and then go quickly; north stays cold longest.

Plan the route around aspect and time together: climb the aspect that will be firm on the way up, ski the aspect that will be softening as you descend, and be off both before they are wet.

The reliable rule: when you start sinking in past your boot, the window has shut. Descend.

Other spring hazards

Cornices fail readily in the afternoon warmth. Stay well back on ridges and do not linger beneath them.

Glide cracks — the whole snowpack sliding slowly on a smooth ground surface — open in spring, and glide avalanches release with essentially no warning and no reliable prediction. Do not travel under or camp beneath an open glide crack.

Snow bridges over creeks and crevasses weaken through the day. A crossing that held in the morning may not hold in the afternoon.

Sun. Reflected ultraviolet off snow at altitude is intense. Sunburn under the chin and in the nostrils is a spring speciality, and snow blindness is a real and miserable injury. Good glasses, high-factor sun cream, applied repeatedly.

Water. You will need more than you think. Warm days, long climbs and dry air at altitude add up.

The mindset shift

Winter touring is dominated by snowpack assessment: what layers are in there, what is the forecast problem. Spring touring is dominated by the clock and the thermometer.

The question changes from "is this slope stable" to "how long until this slope stops being stable, and will I be off it by then". That is a different discipline and, once you have it, spring offers some of the most reliable and most enjoyable conditions of the whole year.