Weather
Wind and its effects
The felt temperature, or wind chill index, is the temperature we would need in calm conditions to experience the same cold as under the existing wind and temperature conditions (the Norwegian Meteorological Institute, n.
Contents
Effective temperature
The felt temperature, or wind chill index, is the temperature we would need in calm conditions to experience the same cold as under the existing wind and temperature conditions (the Norwegian Meteorological Institute, n.d. a).
The table shows how wind makes the felt temperature colder. This is due to conduction. NB! The table is somewhat offset between air temperature and index. Read the table carefully! Table: the Norwegian Meteorological Institute
Risk of frostbite
The table shows when there is a risk of frostbite, along with good advice for avoiding frostbite. The table is taken from the Norwegian Meteorological Institute (n.d. a).
| Effective temperature | Degree of danger | Effect on the body | Good advice |
|---|---|---|---|
| 0 to -10 | Slight | Mild discomfort | Dress warmly with the outdoor temperature in mind. |
| -10 to -25 | Moderate | Uncomfortable. Bare skin feels cold. Risk of hypothermia during longer stays without suitable protection | Dress warmly. Windproof outer garments are important. Remember headwear, a scarf and mittens; and keep moving. |
| -25 to -45 | High | Risk of frostbite, watch your fingers and toes, your face (especially the nose and ears for numbness and a white colour). Risk of hypothermia during longer stays without suitable protection. | Dress warmly, preferably several layers with windproof outer garments. Cover all bare skin, especially the face and hands. Wear headwear, mittens, a scarf; ideally a balaclava. Avoid bare skin facing the wind and keep moving. |
| -45 to -59 | Extreme | Bare skin can freeze within minutes; check the face, arms and legs frequently for numbness and a white colour (frostbite). High risk of hypothermia* during longer stays outdoors. | Take care! Dress very warmly, several layers with a windproof garment on the outside. Cover all bare skin with suitable clothing, especially the face and hands. Limit outdoor activities to short periods, be prepared to limit or cancel outdoor activities. Keep moving the whole time. |
| -60 and colder | Extreme | Outdoor conditions are life-threatening, bare skin can freeze in less than two minutes. | Stay indoors. |
This is how long it takes to get frostbite, in minutes
The scale shows how long it takes to get frostbite, counted in minutes. Table: Gina Wigestrand, Snuitide. Made on the basis of a table on Yr.
| Colour code | Degree of danger | Minutes before frostbite |
|---|---|---|
| Star * | Very slight | Frostbite unlikely |
| Grey | Slight | 11 —> |
| Light purple | Moderate | 6 - 10 |
| Pink | High | 3 - 5 |
| Purple | Extreme | 1- 2 |
The Beaufort scale – the effects of wind
The Beaufort wind scale is used to indicate wind force by name and number. The strength designations and speed intervals in the table refer to the mean value of the wind, that is, the average wind force. In a further development of the Beaufort wind scale, the effect the wind can be expected to have is also indicated (Seter and the Norwegian Meteorological Institute, 2021).
| Wind force in knots | Norwegian designations | Beaufort | Metres per second | In the mountains | At sea | On land |
|---|---|---|---|---|---|---|
| < 1 | Calm | 0 | 0.0–0.2 | Snowflakes drift down more or less straight, often in a swinging motion. | The sea is mirror-smooth (glassy calm) | Smoke rises straight up |
| 1–3 | Light air | 1 | 0.3–1.5 | Just perceptible. It is clear that the snowflakes are drifting with the wind. | Ripples form on the surface of the sea | The wind direction is shown by the drift of smoke |
| 4–6 | Light breeze | 2 | 1.6–3.3 | Clearly perceptible in severe cold. The snowflakes move more horizontally than vertically. | Small, short, but distinct waves with smooth crests that do not break | Felt, stirs the leaves of trees, lifts a pennant |
| 7–10 | Gentle breeze | 3 | 3.4–5.4 | The wind is clearly noticeable and can be a nuisance. Falling snow appears to move much faster horizontally than vertically. | Small, short, but distinct waves with smooth crests that do not break | Leaves and small twigs stir, the wind stretches light flags and pennants |
| 11–16 | Moderate breeze | 4 | 5.5–7.9 | Unpleasant in cold weather and gives noticeable resistance. Falling snow swirls along with the wind. The drifting snow against the face is very bothersome. | The waves grow longer. Some foam crests | Lifts dust and loose paper, stirs twigs and small branches, stretches larger flags and pennants |
| 17–21 | Fresh breeze | 5 | 8.0–10.7 | It becomes hard work to ski into the weather. Drifting wind-blown snow along the ground is whirled up so high that visibility is reduced. The drifting snow lashes the face. | Medium-sized waves with a more pronounced elongated form and many foam crests. Spray from the tops can occur | Small trees in leaf begin to sway |
| 22–27 | Strong breeze | 6 | 10.8–13.8 | It is very tiring to make headway into the weather. Drifting snow reduces visibility to under 1 km. Difficult to hold an unprotected face into the wind for any length of time. Most people should not set out on a trip across the open mountains at this and higher wind forces. | Large waves begin to form. The foam crests are larger everywhere. Often some spray | Large branches and smaller trunks stir, the telephone wires whine, you feel resistance when walking |
| 28–33 | Near gale | 7 | 13.9–17.1 | Into a headwind you have to lean forward over your skis and put great force into your pole strokes, even on flat ground. It can be difficult to stay on your feet in the gusts. Drifting snow reduces visibility to a few hundred metres. Difficult to orientate yourself in the terrain. A ski trip in the mountains at wind force 7 is a great strain for most people. | The sea heaps up, and white foam from breaking wave tops begins to blow in streaks in the wind direction | Whole trees stir, awkward to walk into the wind |
| 34–40 | Gale | 8 | 17.2–20.7 | The mountain is in a turmoil. Twigs and lichen from the trees drift with the wind. Very difficult to ski. Almost impossible to carry the skis on your shoulders. Drifting snow reduces visibility to under 100 m. Impossible to orientate yourself in the terrain. Very difficult to follow even well-staked trails. Do not set out on a trip! | Moderately high waves of greater length. The wave crests begin to break up into spindrift, which drifts in clearly marked streaks with the wind | Breaks twigs off the trees, hard to walk into the wind |
| 41–47 | Strong gale | 9 | 20.8–24.4 | Wind and drifting snow make it impossible to make headway on skis across the mountains. Even in clear weather and little drifting snow the strain can become so great that a snow cave or cabin is the only refuge. | High waves. Dense streaks of foam drift in the wind direction. The sea begins to ‘roll’. The spindrift can reduce visibility | Whole large trees sway and heave, roof tiles can be blown down |
| 48–55 | Storm | 10 | 24.5–28.4 | This and higher wind forces are something most people will never encounter. Trees fall over telephone and power lines. Log walls creak. Light small houses are torn from their foundations. | Very high waves with long overhanging crests. The foam drifts with the wind in dense white streaks, so that the sea takes on a whitish appearance. The rolling becomes heavy and jolting. Visibility is reduced | Rare inland, trees are uprooted, great damage to houses |
| 56–63 | Violent storm | 11 | 28.5–32.6 | Roads and railway lines are blocked. There is chaos on the telephone and power networks. Forest is laid waste. | Exceptionally high waves (small and medium-sized ships can disappear for a time in the wave troughs). The sea is completely covered with long white sheets of foam lying in the direction of the wind. Everywhere the wave crests are blown into froth-like foam. | Very rare, accompanied by great destruction |
| > 63 | Hurricane | 12 | > 32.6 | If a built-up area is hit, it becomes a natural disaster that will often claim several human lives. | The air is filled with foam and spray that reduces visibility considerably. The sea is completely white with drifting foam | Extremely rare. Unusually great destruction |
(Seter and the Norwegian Meteorological Institute, 2021)
Next steps
- Weather forecasting — checking wind forecasts
- The trip meteorologist — interpreting the wind in the forecast
- Avalanches — The weather — wind and avalanche danger in winter
- Winter clothing — dressing against the wind
Learn more
- Yr.no — the Norwegian Meteorological Institute’s weather forecast
- The Norwegian Meteorological Institute — specialist material and research
- Varsom — hazard warnings (avalanches, floods, landslides)
- Storm Geo — commercial meteorology