Definition
A wind that blows up the side of rising terrain, such as a mountain slope or hillside. As the air is forced upward along the surface, it cools and expands, and if it rises far enough it may reach saturation, producing clouds, fog, or precipitation on the windward face of the terrain.
Plain English
Wind that pushes air up the side of a hill or mountain. As the air goes up it cools, and that often forms cloud, mist, or rain along the rising ground.
Context Anchor
Seen in mountain weather, ridge flying, and airport weather discussions near hills or rising terrain.
Derivation
From 'up' plus 'slope' (the angled surface of terrain). The name simply describes what the wind is doing: moving up a slope. Naming it this way distinguishes it from a downslope wind, which flows down the same terrain and behaves very differently.
Why Pilots Care
These winds can create clouds, reduced visibility, precipitation, and turbulence that affect routes and safety in mountainous areas.
Grounding Statement
Picture wind hitting the eastern foothills of a mountain range; it has nowhere to go but up the slope, cooling as it climbs and often forming a deck of cloud against the high ground.
Intuition Check
Upslope wind does not mean the airplane is climbing into the wind. It means the wind itself is moving uphill along the terrain.
Example Sentence 1
An upslope wind off the plains was forecast to bring low ceilings and light snow to the foothills throughout the afternoon.
Example Sentence 2
During preflight the pilot checked for upslope flow that could bring fog into the valley from the nearby range.