Wind can make it feel significantly colder than the measured air temperature. This is one of the reasons that an ultralight windshirt can seem to provide a significant amount of warmth. On a recent trip to Iceland we face nearly continuous strong winds which required more clothing than I normally wear. I wanted to recalibrate my expectations of the comfort range for my clothing. To do this I reviewed how wind impacts temperature perception.
The first step was to discover what the wind speed was which is required to calculate windchill. Based on weather station data and observations I learned we faced continuous 20mph winds. In some locations the wind was regularly 30mph with gusts which exceeded 45mph.
I found that high winds seemed to cool me more than wind chill would predict. For example, I am typically comfortable walking in a pair of OR Ferrosi Pants down to freezing… but when facing 25mph winds in 50F temperatures I really appreciated wearing my rain pants which would normally cause me to overheat.
The following was largely generated via chat-gpt with some additional integration and additions based of some reference material.
Wind Speed
There are a number of scientific instruments which will measure windspeed… but they tend to be expensive and somewhat bulky. You can often get wind data through smartphone apps and websites which access weather stations. It’s also possible to estimate wind speed by observing how the wind is effecting the environment.
The Beaufort Scale is the standardized scale used to estimate wind speed based on observed conditions at sea or on land. It was originally developed in 1805 by Sir Francis Beaufort, a British naval officer, and has been widely adopted for maritime and meteorological purposes. The scale ranges from 0 to 12, with each level corresponding to specific wind speeds and associated observable effects.
- Calm: less than 1 mph (0-1.5 km/h)
- Land Observations: Smoke rises vertically, leaves are motionless.
- Sea Observations: Sea surface is smooth and mirror-like.
- Light Air: 1-3 mph (1.6-5 km/h)
- Land Observations: Smoke drifts, wind direction shown by smoke.
- Sea Observations: Ripples with the appearance of scales, no foam crests.
- Light Breeze: 4-7 mph (6-11 km/h)
- Land Observations: Leaves rustle, wind felt on face, flags start to extend, wind socks less than 45 degree angle
- Sea Observations: Small wavelets, crests do not break.
- Gentle Breeze: 8-12 mph (12-19 km/h)
- Land Observations: Leaves and small twigs in constant motion, light flags extended, wind sock at 45 degree angle.
- Sea Observations: Large wavelets, crests begin to break.
- Moderate Breeze: 13-18 mph (20-28 km/h)
- Land Observations: Small branches move, dust and loose paper raised, flags fly straight out. Smoke blows downwind and may be dispersed.
- Sea Observations: Small waves with breaking crests, some foam.
- Fresh Breeze: 19-24 mph (29-38 km/h)
- Land Observations: Small trees sway, crested waves form on inland waters, windsock will be at a 90 degree angle.
- Sea Observations: Moderate waves, many whitecaps, some spray.
- Strong Breeze: 25-31 mph (39-49 km/h)
- Land Observations: Large branches sway, wires whistle, walking against wind resistance felt. You might need to lean slightly forward to maintain balance and push against the wind. Flag flutters vigorously and may snap in the wind.
- Sea Observations: Large waves, extensive whitecaps, some spray.
- Near Gale: 32-38 mph (50-61 km/h)
- Land Observations: Whole trees in motion, inconvenience felt walking against wind. The wind may push you off balance, especially if it is gusty. You will likely need to exert significant effort to walk into the wind, and side winds might push you sideways.
- Sea Observations: Sea heaps up, foam blown in streaks.
- Gale: 39-46 mph (62-74 km/h)
- Land Observations: Twigs break off trees. Strong winds can make it hard to maintain balance, and you may be forced to stop or hold onto something to avoid being blown over. Gusts can catch you off guard and push you off course.
- Sea Observations: Moderately high waves, foam begins to be blown in dense streaks.
- Strong Gale: 47-54 mph (75-88 km/h)
- Land Observations: Slight structural damage occurs, branches break off trees.
- Sea Observations: High waves, dense foam streaks, rolling seas.
- Storm: 55-63 mph (89-102 km/h)
- Land Observations: Trees uprooted, considerable structural damage.
- Sea Observations: Very high waves with long overhanging crests, heavy sea spray.
- Violent Storm: 64-72 mph (103-117 km/h)
- Land Observations: Widespread damage, You may find it impossible to walk against the wind, and the force could knock you over.
- Sea Observations: Exceptionally high waves, sea completely covered with foam.
- Hurricane Force: 73+ mph (118+ km/h)
- Land Observations: Severe and extensive damage.
- Sea Observations: Air filled with foam and spray, sea white with driving spray.
Wind Chill
The wind chill formula calculates the perceived decrease in air temperature felt by the body due to the flow of air.
Wind Chill Temperature (°F)=35.74+0.6215T−35.75(V^0.16)+0.4275T(V^0.16)
Where:
- T is the air temperature in degrees Fahrenheit (°F).
- V is the wind speed in miles per hour (mph).
In chart form:
| T/V | 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 | 45 | 50 | 55 | 60 |
| 50 | 48.2 | 46.0 | 44.6 | 43.6 | 42.8 | 42.0 | 41.4 | 40.9 | 40.4 | 39.9 | 39.5 | 39.1 |
| 45 | 42.3 | 39.8 | 38.2 | 37.0 | 36.1 | 35.3 | 34.5 | 33.9 | 33.3 | 32.8 | 32.4 | 31.9 |
| 40 | 36.5 | 33.6 | 31.8 | 30.5 | 29.4 | 28.5 | 27.7 | 26.9 | 26.3 | 25.7 | 25.2 | 24.7 |
| 35 | 30.6 | 27.4 | 25.4 | 23.9 | 22.7 | 21.7 | 20.8 | 20.0 | 19.3 | 18.6 | 18.0 | 17.5 |
| 30 | 24.7 | 21.2 | 19.0 | 17.4 | 16.0 | 14.9 | 13.9 | 13.0 | 12.2 | 11.5 | 10.9 | 10.2 |
| 25 | 18.9 | 15.1 | 12.6 | 10.8 | 9.3 | 8.1 | 7.0 | 6.1 | 5.2 | 4.4 | 3.7 | 3.0 |
| 20 | 13.0 | 8.9 | 6.2 | 4.2 | 2.6 | 1.3 | 0.1 | -0.9 | -1.8 | -2.7 | -3.5 | -4.2 |
| 15 | 7.1 | 2.7 | -0.2 | -2.3 | -4.0 | -5.5 | -6.8 | -7.9 | -8.9 | -9.8 | -10.6 | -11.4 |
| 10 | 1.2 | -3.5 | -6.6 | -8.9 | -10.7 | -12.3 | -13.6 | -14.8 | -15.9 | -16.9 | -17.8 | -18.6 |
| 5 | -4.6 | -9.7 | -13.0 | -15.4 | -17.4 | -19.1 | -20.5 | -21.8 | -23.0 | -24.0 | -25.0 | -25.9 |
| 0 | -10.5 | -15.9 | -19.4 | -22.0 | -24.1 | -25.9 | -27.4 | -28.8 | -30.0 | -31.1 | -32.1 | -33.1 |
| -5 | -16.4 | -22.1 | -25.8 | -28.6 | -30.8 | -32.7 | -34.3 | -35.7 | -37.0 | -38.2 | -39.3 | -40.3 |
| -10 | -22.3 | -28.3 | -32.2 | -35.1 | -37.5 | -39.4 | -41.2 | -42.7 | -44.1 | -45.3 | -46.5 | -47.5 |
| -15 | -28.1 | -34.5 | -38.6 | -41.7 | -44.1 | -46.2 | -48.1 | -49.7 | -51.1 | -52.4 | -53.6 | -54.8 |
| -20 | -34.0 | -40.7 | -45.0 | -48.2 | -50.8 | -53.0 | -54.9 | -56.6 | -58.1 | -59.5 | -60.8 | -62.0 |
| -25 | -39.9 | -46.9 | -51.4 | -54.8 | -57.5 | -59.8 | -61.8 | -63.6 | -65.2 | -66.6 | -68.0 | -69.2 |
| -30 | -45.7 | -53.1 | -57.8 | -61.4 | -64.2 | -66.6 | -68.7 | -70.6 | -72.2 | -73.7 | -75.1 | -76.4 |
| -35 | -51.6 | -59.3 | -64.2 | -67.9 | -70.9 | -73.4 | -75.6 | -77.5 | -79.3 | -80.8 | -82.3 | -83.7 |
| -40 | -57.5 | -65.5 | -70.6 | -74.5 | -77.6 | -80.2 | -82.5 | -84.5 | -86.3 | -87.9 | -89.5 | -90.9 |
