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Wind Chill Index or 'chilled' temperature of air in movement - the wind chill index
The cooling or
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The convective heat loss due to wind can be dramatic. In the table below the wind chill effect is illustrated for air velocities up to 10 m/s (2000 ft/min), or "fresh breeze" according the Beaufort wind scale.
| Air velocity | Chill effect | ||
|---|---|---|---|
| (m/s) | (ft/min) | (oC) | (oF) |
| 0.1 | 20 | 0 | 0 |
| 0.25 | 50 | 0.5 | 2 |
| 1.5 | 300 | 4 | 7 |
| 3 | 600 | 6 | 10.5 |
| 5 | 1,000 | 7 | 13 |
| 8 | 1,575 | 8 | 15 |
| 10 | 2,000 | 9 | 16 |
Wind Chill Index - Wind Velocity km/h and degrees Celsius
The "Chilled" air temperature can also be expressed as a function of wind velocity and ambient air temperature as
twC = 13.12 + 0.6215 ta - 11.37 v0.16 + 0.3965 ta v0.16 (1)
where
twC = effective "wind" temperature (oC)
ta = air temperature (oC)
v = wind velocity (km/h)
| "Chilled" Air Temperature (oC) | ||||||||
|---|---|---|---|---|---|---|---|---|
| Ambient Air Temperature (oC) | Wind Velocity (km/h) | |||||||
| 5 | 10 | 15 | 20 | 30 | 40 | 50 | 60 | |
| 10 | 10 | 9 | 8 | 7 | 7 | 6 | 5 | 5 |
| 5 | 4 | 3 | 2 | 1 | 0 | -1 | -1 | -2 |
| 0 | -2 | -3 | -4 | -5 | -6 | -7 | -8 | -9 |
| -5 | -7 | -9 | -11 | -12 | -13 | -14 | -15 | -16 |
| -10 | -13 | -15 | -17 | -18 | -20 | -21 | -22 | -23 |
| -15 | -19 | -21 | -23 | -24 | -26 | -27 | -29 | -30 |
| -20 | -24 | -27 | -29 | -30 | -33 | -34 | -35 | -36 |
| -25 | -30 | -33 | -35 | -37 | -39 | -41 | -42 | -43 |
| -30 | -36 | -39 | -41 | -43 | -46 | -48 | -49 | -50 |
| -35 | -41 | -45 | -48 | -49 | -52 | -54 | -56 | -57 |
| -40 | -47 | -51 | -54 | -56 | -59 | -61 | -63 | -64 |
- 1 km/h = 0.2778 m/s = 54.68 ft/min = 0.6214 mph = 0.5396 knot
Wind Chill Index - Wind Velocity mph and degrees Fahrenheit
The "Chilled" air temperature can also be expressed as a function of wind velocity and ambient air temperature as
twF = 35.74 + 0.6215 ta - 35.75 v0.16 + 0.4275 ta v0.16 (2)
where
twF = effective temperature (oF)
ta = air temperature (oF)
v = wind velocity (mph)
| "Chilled" Air Temperature (oF) | ||||||||
|---|---|---|---|---|---|---|---|---|
| Ambient Air Temperature (oF) | Wind Velocity (mph) | |||||||
| 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 | |
| 40 | 36 | 34 | 32 | 30 | 29 | 28 | 28 | 27 |
| 35 | 31 | 27 | 25 | 24 | 23 | 21 | 21 | 20 |
| 30 | 25 | 21 | 19 | 17 | 16 | 14 | 14 | 13 |
| 25 | 19 | 15 | 13 | 11 | 9 | 7 | 7 | 6 |
| 20 | 13 | 9 | 6 | 4 | 3 | 0 | 0 | -1 |
| 15 | 7 | 3 | 0 | -2 | -4 | -7 | -7 | -8 |
| 10 | 1 | -4 | -7 | -9 | -11 | -14 | -14 | -15 |
| 5 | -5 | -10 | -13 | -15 | -17 | -21 | -21 | -22 |
| 0 | -11 | -16 | -19 | -22 | -24 | -27 | -27 | -29 |
| -5 | -16 | -22 | -26 | -29 | -31 | -37 | -34 | -36 |
| -10 | -22 | -28 | -32 | -35 | -37 | -41 | -41 | -43 |
| -15 | -28 | -35 | -39 | -42 | -44 | -48 | -48 | -50 |
| -20 | -34 | -41 | -45 | -48 | -51 | -55 | -55 | -57 |
| -25 | -40 | -47 | -51 | -55 | -58 | -62 | -62 | -64 |
| -30 | -46 | -53 | -58 | -61 | -64 | -69 | -69 | -71 |
| -35 | -52 | -59 | -64 | -68 | -71 | -76 | -76 | -78 |
| -40 | -57 | -66 | -71 | -74 | -78 | -82 | -82 | -84 |
| Wind Chill | Possible Effects |
|---|---|
| 30oF or higher | Generally unpleasent |
| 30o to 15oF | Unpleasent |
| 14o to 0oF | Very unpleasent |
| -1o to -20oF | Frostbite possible |
| -21o to -60oF | Frostbite likely - outdoor activities dangerous |
| -61o or lower | Exposed flesh freezes within 30 seconds |
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