Orographic lift: why one side of a range gets more snow

Orographic lift is what happens when wind pushes moist air up the side of a mountain range. The air cools as it rises, its moisture condenses, and it drops snow on the slopes facing the wind. By the time the air crosses the crest it has lost much of its moisture, so the far side, the lee, usually gets less. That is why two ski areas a short drive apart can report very different totals from the same storm.

Windward, leeward and the rain shadow

• Windward slopes face into the incoming storm. Rising air cools and squeezes out snow, so they generally see the most.
• The crest often does well too, because air is still rising as it reaches the top.
• Leeward slopes sit on the far side. Air sinks and warms there, clouds thin out, and snowfall drops off. A strongly dry lee is called a rain shadow.

The effect is strongest when the wind blows straight at a range, when the wind is strong, and when the air is moist. A storm arriving from an unusual direction can reverse the usual pattern and favor mountains that normally miss out.

When sinking air on the lee side is also warm and windy, it can become a Chinook. Chinook winds and snow covers what that does to the snowpack.

Why forecasts struggle with it

Orographic snow depends on terrain details that weather models smooth over. A coarse model may treat a range as a broad hill and spread snow too evenly across both sides. Finer models capture more of the terrain but cover shorter time ranges. This is one reason forecasts for the same mountain can disagree; see why snow forecasts disagree.

What SkiBuds does, and deliberately does not, do

The SkiBuds forecast engine contains a terrain-alignment calculation that compares wind direction with the direction a slope faces. It does not use it to change snowfall totals yet. In the current forecast the orographic adjustment is fixed at no change: the engine keeps each source's own amount for each elevation, because neither surface wind direction nor an unverified wind reading from higher in the atmosphere proves how much more snow a windward slope will get.

A correction like this can make a forecast look more precise while making it less accurate. SkiBuds will only apply one once it has been checked against observed snowfall. Until then, the base, mid-mountain and summit views in the app show the forecast sources' elevation amounts without an extra terrain multiplier.

How to use storm direction when choosing a mountain

• Read the storm track, not just the total. Note where the wind is coming from as the storm arrives. Mountains facing that direction are the likely winners.
• Compare sides of a range. If one side of a pass usually gets more snow from westerly storms, an easterly or upslope storm can flip that.
• Favor elevation and the crest when snow levels are marginal. Rising air at the top keeps producing snow even when lower slopes are borderline.
• Check observations after the storm. Measured snowfall and the resort's report settle which side actually did best; see snow depth vs snowfall vs SWE.

How to read a ski resort snow forecast explains base, mid-mountain and summit forecasts, and the mountain region guides help you compare nearby resorts. The SkiBuds app is being rebuilt for iOS and Android and is coming soon.