Katabatic winds blow downhill, while Anabatic winds blow uphill. Use whatever crazy mnemonic you like, but I always imagine a cat (katabatic) rolling down a hill.

Katabatic winds are caused when air above a slope is cooled, becomes denser, and then flows down the slope to replace warmer air below, such as in a valley. You might experience this if you are kayaking in a lake or river at the bottom of such a valley. In some cases, the cooling of air at the top of a mountain is caused by the lower temperature at that altitude. Snow or ice at elevation may contact the air, causing it to cool. The cooler, denser air then falls down the slope under the force of gravity.

Anabatic winds are caused when the air above a hillside or mountaintop is heated, causing it to become less dense, and therefore rise to replace denser air above. For example, over the course of a day, the sun may beat down on a hillside, causing the air above the hillside to become warmer. By the time afternoon comes around, the heated air is moving up, which may be towards the peak of the hill, or may be upstream in a river valley. If you are kayaking in a lake or river at the bottom of the hillside, you may perceive this as a wind blowing upstream or towards shore.

Anabatic (uphill) winds tend to occur in the daytime, while katabatic (downhill) winds occur in the evenings. Katabatic winds are potentially stronger and faster than anabatic winds. If you are hit by some crazy wind, you can look for slopes around you along with areas where some uneven heating of the air might be occurring. True, it might not save you from having to paddle through it, but you can file in the back of your brain for future reference.

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