Local winds
What Is Katabatic Wind? Night Winds Off High Land
Published · Last checked October 2026
A katabatic wind is cold, dense air flowing downhill under gravity, usually at night when high ground cools. It pours down slopes and valleys and out over the water near the coast. Most UK katabatics are light to moderate breezes, but off steep mountains, fjords and lochs they can arrive suddenly and gust strongly, catching out boats at anchor in apparently sheltered bays.
How katabatic wind forms
On a clear night, land loses heat quickly by radiation. The air in contact with high ground cools, becomes denser than the air around it and starts to slide downhill, much like water. Valleys funnel the flow, so the strongest katabatic winds come out of valley mouths, lochs and gaps in mountain ranges.
The opposite effect, warm air rising up slopes during the day, is called an anabatic wind and is usually weaker. Both are local winds driven by heating and cooling, like the sea breeze and land breeze.
When and where to expect it
- Clear, calm nights, when the land cools fastest.
- Steep high ground near the sea: Scottish sea lochs, Norwegian fjords, Mediterranean mountain coasts and the Lake District.
- Valley mouths and gaps, where the cold air is funnelled.
- Snow-covered or very high land, which can drive much stronger flows.
| Wind | When | Direction | Typical strength in the UK |
|---|---|---|---|
| Sea breeze | Sunny afternoons | Sea to land | Force 3 to 4, sometimes more |
| Land breeze | Clear nights | Land to sea | Light |
| Katabatic | Clear nights | Downhill, out to sea | Light to moderate; can be strong off mountains |
| Anabatic | Sunny days | Uphill | Light |
Some famous strong winds are partly katabatic, such as the Bora on the Adriatic coast of Croatia, which can rise to gale force with little warning and is a real hazard for cruising yachts.
What it means for sailors
The danger is surprise. You anchor in a calm bay under a hillside, expecting a quiet night, and in the small hours a strong, gusty wind starts pouring off the land. In a loch, it can whip up a short chop over a surprisingly short fetch, and in a fjord it may blow straight out of the valley across your anchorage.
- Look at the chart and terrain around an overnight anchorage: steep slopes and valley mouths are warning signs.
- Lay out ample scope and set the anchor well. See how to anchor a yacht.
- Choose a spot where an offshore katabatic would blow you out to open water, not onto rocks.
- Set an anchor alarm and keep a watch if you are uneasy.
- In the Mediterranean, read local forecasts for named winds like the Bora.
The anchoring lesson and weather awareness lesson cover choosing a safe overnight spot.