Waves off the west coast of Scotland have reached heights of around 20 metres (65ft) amid warnings of severe weather from forecasters.
Researchers recording waves off the north-west coast of the Isle of Lewis said average peaks measured between 13 and 14 metres (42-45ft) during the day. It comes as high winds and snow were predicted to hit much of Scotland on Monday, with conditions in the mountains described as "atrocious".
A number of sensors in the sea monitor wave frequency and direction all year round as part of the Hebridean Marine Energy Futures project based at Lews Castle College in Stornoway.
Senior research engineer Arne Vogler said: "It gives us a very good understanding of what is going on out there and I have to say it is pretty horrendous.
"During the winter we would see five or six metre (16-19ft) waves, that is quite normal. Then we get your everyday gale and they would go up to seven or eight (22-26ft). But we have strong westerly winds, with gusts up to hurricane force and waves of 20 metres, with an individual wave of 21.8 metres (72ft) at around 11.30am."
The Met Office issued amber "be prepared" warnings for snow for the Highlands and Western Isles, Strathclyde, the South West, Lothian and Borders, Central, Tayside and Fife. Forecasters said some heavy showers and blizzards could be expected at times, with up to 10 to 20cm of snow accumulations on higher-level routes.
It said exposed areas on the west coast are also likely to see unusually high sea and swell conditions as a yellow "be aware" alert for high winds was put in place in many regions including Orkney and Shetland, the Highlands, Western Isles and Strathclyde.
Julian Mayes, a forecaster with MeteoGroup, the weather division of the Press Association, said: "It's going to be windy throughout the day, with the highest wind speeds on the west coast. There will be maximum gusts of 60 to 70mph at any time today and this evening."
Transport minister Keith Brown said: "Looking at the latest Met Office forecast for frequent and at times heavy snow combined with gales force winds will mean a testing journey for many."
Many ferry services faced disruption, with cancellations in the Western Isles, including the Oban to Lochboisdale sailing. Ferries to Orkney and Shetland were also affected. The strong winds forced the closure of the Forth Road Bridge, the Erskine Bridge, Clackmannanshire Bridge and Skye Bridge to high vehicles.