Definition
A warm, dry downslope wind that flows down the eastern side of the Rocky Mountains. As moist air is forced up the windward side of the range, it cools and drops most of its moisture as precipitation. The now-dry air descends the leeward side, compressing and warming rapidly, often producing dramatic temperature rises at the surface in a short period of time.
Plain English
A warm, dry wind that blows down the east side of the Rockies. It can raise the temperature on the ground by tens of degrees in just a few hours.
Context Anchor
Seen in weather discussions for mountain and foothill flying, especially near the Rocky Mountains.
Derivation
Named after the Chinook people of the Pacific Northwest. Early settlers used the name for the warm wind that seemed to come from the direction of Chinook territory. The name stuck as a label for any warm, dry downslope wind on the lee side of a mountain range.
Why Pilots Care
Sudden warming reduces air density and can quickly raise density altitude, lowering aircraft performance and potentially creating turbulence or wind shear near mountain ridges.
Grounding Statement
Imagine air being squeezed as it sinks down the back of a mountain range -- the squeezing heats it up, so what arrives at the foot of the slope is warm, dry, and often gusty.
Intuition Check
Do not assume Chinook means the helicopter here. In this weather context, it means a warm, dry downslope wind.
Example Sentence 1
The forecast called for a Chinook to develop overnight, so we expected the morning temperature at Calgary to climb well above freezing.
Example Sentence 2
Approaching the Front Range, the crew monitored for Chinook conditions that could produce strong downdrafts on the lee side of the mountains.