Strong winds can increase the rate of heat loss in cold weather. Wind chill attempts to score this effect based on the effect of wind on human skin exposure. To calculate the coolness of the wind in your home, all you need is temperature and wind speed measurements. Both can be taken from the weather forecast. You can even measure wind speed at home using just a small paper cup and a plastic straw.
Step
Method 1 of 3: Calculating Wind Coolness Yourself
Step 1. Measure the temperature T
Use a thermometer or check the current outdoor temperature from a weather forecast site. You can measure temperature in degrees Fahrenheit or Celsius, but read the next step carefully to find out which unit to use for wind speed.
Wind chill is undefined for temperatures below 50 F (10 C). If the temperature is higher, the wind has little effect on the apparent temperature
Step 2. View or measure the wind speed, V
You can find wind speed forecasts in your area from most weather forecasting sites, or by typing "wind speed + (name of your city)" in a search engine. You can measure wind speed using an anemometer (you can make your own using the instructions below). If you are using F for temperature measurement, use wind speed measurement in miles per hour (mph). If you use C, use kilometers per hour (km/h). If necessary, use this website to convert from knots to km/h.
- If you are using an official wind speed measurement taken at a value of 10 meters, multiply it by 0.75 to get a rough estimate of the wind speed at a value of 1.5 m, a common height for a human face.
- Winds below 3 mph (4.8 km/h) had no significant wind cooling effect.
Step 3. Plug these values into the formula
There are several wind coolness formulas that have been used for years and are used in various regions, but we will use one of the formulas currently used by the UK, US and Canada, This formula was created by an international team of researchers. Plug all values into the formula below, replacing T with temperature and V with wind speed:
- If you use F and mph: wind chill temperature = 35.74 + 0.6215 T - 35, 75 V0, 16+ 0, 4275 TV0, 16
- If you use C and km/h: wind chill temperature = 13.12 + 0.6215 T - 11, 37 V0, 16+ 0, 3965 TV0, 16
Step 4. Adjust the sunlight
Bright sunlight can increase the apparent temperature by +10 to +18ºF (+5.6 to +10ºC). There is no official formula for measuring this effect, but be aware that sunlight will make the air appear warmer than the coolness formula suggests.
Step 5. Understand what wind chill means
Wind chill is a concept created to describe how wind increases heat loss in exposed skin. In extreme conditions, this can be a major factor in measuring how quickly frostbite takes effect. At wind chill temperatures below -19 F (-28 C), frostbite will develop on exposed skin in 15 minutes or less. Below -58 F (-50ºC), exposed skin can freeze within 30 seconds.
Method 2 of 3: Using a Wind Coolness Calculator
Step 1. Look for wind chill calculators online
Try using the calculator at the US National Weather Service, freemathhelp.com, or onlineconversion.com.
All of these calculators use the wind chill formula which was recently adopted by the US and other countries in 2001. If you use a different calculator, try to find one that also uses this formula; old formulas can give misleading results
Step 2. Look at the temperature and wind speed
Both types of information are usually available from weather forecasting websites, television stations, radio stations, and newspapers.
Step 3. Multiply the wind speed by 0.75
Unless the forecast determines the wind speed at ground level, multiply the speed by 0.75 to get a more accurate estimate of the wind speed at human face height.
This estimate is based on a standard wind speed measurement height of 10 meters, and general atmospheric conditions. Using wind speed measured at a height of 1.5 meters will be more accurate, but can usually only be done with the help of an anemometer
Step 4. Enter all values into the calculator
Make sure you select the unit (such as mph or C) that fits your measurement. Click 'OK or similar button, and you will see the new pseudo-wind coolness temperature.
Method 3 of 3: Measuring Wind Speed
Step 1. Decide whether to make or buy an anemometer
Anemometer is a tool to measure wind speed. You can buy it online, or easily make your own in about 30 minutes using the steps below. If you bought one, skip to the step to calculate the rotation, or just read the wind speed directly if you have a digital display.
Step 2. Make a hole in the small paper cup
Take four small paper cups, and make a hole in each one about 1.25 cm from under the rim of the glass. Take the fifth glass, then pierce four holes with the same distance, about 6 mm below the rim of the glass, then make a fifth hole in the middle of the bottom of the glass.
You can use a pencil to make holes, if you don't have anything sharper
Step 3. Create half of the base shape
Insert a plastic straw into the hole in the glass, about 2.5 cm deep. Push the end of the straw through the two holes of the five-hole glass. Insert the free end of the straw into another glass with one hole. Rotate the two glasses with one hole so that they are pointing in opposite directions, along the same plane as the straw. Clamp the straw to the glass.
Step 4. Finish the basic shapes
Repeat with another straw, threading it through the remaining two holes of the five-hole glass in the center. Rotate these two new glasses until each glass opening is closer to the bottom of the next. In other words, the top glass is pointing to the right, the right glass is pointing down, the left glass is pointing down, and the left glass is pointing up. Clamp all straws and all glasses.
Step 5. Create the base of the anemometer
Slide the two straws until all four glasses are an equal distance from the center. Insert a small pin through the junction of the two straws. Insert the tip of the eraser into the pencil through the hole in the bottom of the center glass, and gently push it into the pin. Now you can hold the anemometer with the tip of a pencil and use it to measure wind speed.
Step 6. Count the number of rotations that the anemometer creates
Hold the anemometer upright in windy areas. Look at one glass (draw on it with a marker to make it easier to follow) and then count the number of times the glass rotates. Use a stopwatch or have a friend watch the seconds hand tick for 15 seconds, then stop when the time is up. Multiply your count by four to get the number of revolutions per minute (rpm).
For greater accuracy, count the number of rotations in 60 seconds (and do not multiply by anything)
Step 7. Calculate the circumference
Measure the distance from one edge of the anemometer to the other to find the diameter of the rotating circle, d. The circumference of a circle is equal to d. This is the distance covered in one revolution.
If a calculator is not available, you can use a value of 3, 14 as an estimate of, or simply 3 for a rough estimate
Step 8. Calculate the wind speed
Change the calculated circumference to a more useful unit for measuring wind speed (miles or kilometers). Multiply the result by the calculated rpm to get the total distance traveled in one minute. Multiply the result by 60 to get the distance traveled in one hour (mph or km/h). Here is the complete formula, both in imperial and metric units:
- Imperial: (_ circumference _ inches/revolution) * (1/12 ft/inch) * (1/5,280 mile/ft) * (_ rpm _ revolutions/minute) * (60 minutes/hour) = _ wind speed _ in miles per hour.
- Metric: (_ circumference _ cm/revolution) * (1/100,000 kilometers/centimeter) * (_ rpm _ revolutions/minute) * (60 minutes/hour) = _ wind speed _ in kilometers per hour.
Tips
- Wind cools people and objects more quickly than cools in still air, and does not cause the internal temperature to drop below the actual temperature of the surrounding air. Practically speaking, this makes the coolness of the wind useful when talking about humans or animals, but not in inanimate objects that do not generate their own body heat.
- The apparent temperature (rate of heat loss) is also affected by humidity, air pressure, physical activity, and natural differences between individuals. There is currently no general formula that uses these values.
