Refer to figure.
An Anabatic wind is a local air current that blows up a hill or mountain slope during the day.

• The Sun heats such slope and the air in contact with the ground will be heated by conduction and will rise up the hill. Free cold air will replace the lifted air and so a light wind will blow up the hillside.
• An anabatic wind is a light wind of around 5 kt.

A katabatic wind is caused by a flow of cold air down a hill or mountain side at night, when the highlands radiate heat and are cooled.

• The air in contact with the higher-level ground is also cooled, and it becomes denser than the air at the same elevation but away from the slope; it, therefore, begins to flow downhill.
• The katabatic effect is most marked if the mountain side is snow covered, if the sky is clear to assist radiation and if the PG is slack.

Speeds average 10 kt and the flow of cold air into the valley helps frost and fog to form.