Waves are flowing on the WeatherRadar, not in the ocean but in the sky over parts of the UK.

Friday morning, as cloud cover stretched across much of the UK, cool, moist air in the northerly Jet Stream flow was also forced to ascent to higher altitudes producing the phenomenon known as Lee waves.

An oscillating up and down motion of the flow as the airstream interacts with the terrain results in cloud lines, at right angles to the wind direction which appear upon hitting mountainous, or hilly, areas.

Air ascending up a mountain range happens all the time if the wind direction is right. What is crucial during a lee wave event is an inversion, a stable layer of air that acts as a "lid" above the cool, moist air mass below.

Every time the air rises, it cools and forms a cloud that sits at each crest of the wave. When this airflow hits the inversion it subsides and dries again.

Have you seen any near you? If so, send us a picture, we would love to see them. Upload yours here!