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The winter reports by our Fell Top Assessors sometime contain specialised vocabulary, especially about snow conditions. Here are some more details about the words and phrases they use. There's also a table explaining what wind speeds mean in reality:


A projecting build-up of snow that take the form of an overhanging ledge on the lee side of a ridge or where a sharp change in slope angle occurs. One example is where a summit plateau drops away into a corrie. Cornices can be extremely unstable - particularly when freshly formed or whilst thawing. Avoid walking above them.

Cornice and avalanche on Helvellyn summit plateau

Photo: Cornice on Helvellyn summit with an avalanche, caused when the cornice slipped

Cornice cracks

Photo: Can you make out the crack in the cornice?


A type of snow that is formed from supercooled water droplets freezing onto a falling snowflake. Also known as soft hail, graupel appears as small rounded pellets similar in appearance to expanded polystyrene. When trapped between layers of snow, graupel can render the snowpack very unstable, as they can act like ball bearings between the layers.

Graupel - ball-bearing-like snow particles

Photo: Layers of graupel


Snow that has undergone several cycles of thawing and freezing which helps to consolidate the snow pack. This makes the snow strong and stable, creating good underfoot conditions for walking and climbing.

Rime ice

The white icy crust that builds up on the windward side of objects. Rime 'grows' into the wind as super-cooled water droplets freeze on contact with the surface. This often creates creating beautiful, feather-like structures which can grow to a considerable size.


Fine snow, picked up and blown around by the wind that can result in very poor visibility.


Thin, clear ice formed from the freezing of standing water – the mountain equivalent of 'black ice'. Verglas can be treacherous, particularly when hidden under a layer of loose powder snow.

Verglas - the black ice of the mountains copyright Charlie Hedley

Photo: Verglas - the black ice of the mountains

Wind chill

The cooling effect of wind, which makes the air temperature on exposed skin feel much cooler than the air temperature. The effect increases fastest at lower wind speeds up to about 15mph.


Snow that has been re-deposited by the wind. This is in contrast to powder snow which is loose, unconsolidated snow that has fallen in light winds. The turbulence of the wind breaks up the snow crystals and re-deposits them on lee slopes, where considerable accumulations may occur and become very unstable.

Wind speed: what does it mean when you're out on the fells?

Beaufort scale mph kmph What you might see What you may experience
0 Calm 0 0

1-3 Light 1-12 2-20 Surface drift of loose snow
4 Moderate 13-18 21-29

5 Fresh 19-24 30-39 Tree branches in motion
6-7 Strong 25-38 40-61

Wavelets on tarn surfaces

On most 900m summits snow or rain falls horizontally

Severe windchill where the rate of cooling at 0 degrees C is the equivalent of minus 10 degrees C
8 Gale 39-46 62-74 Poor visibility because of blowing snow, known as spindrift Leaning into the wind, your energy output doubles
9 Severe gale 47-54 75-87

Becks blown back uphill

Large trees in motion

Trailing ropes blowing outwards horizontally
10 Storm force 55-63 88-100

Raised whirlwinds of blowing snow on crests

Curtains of water being blown off tarn surfaces

Advice: Keep to lower level walks

Bent double against the wind

Walking is difficult - normal effort trebled

11 Severe storm force 64-72 101-116

Storm shroud of suspended spindrift is 100m (330 feet) thick

Advice: do not venture onto the fells

Extreme windchill
12 Hurricane over 73 over 117

Extensive structural damage

Advice: stay indoors

Needing to crawl in winds more than 80 mph

Humans can be blown off the ground if winds are over 100 mph

Useful links

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