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What is Humidex?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

Humidex is a value which is used to express the perceived temperature by combining temperature and humidity data in one number. The Humidex reflects temperatures in Celsius, because it was developed in Canada. Canadian meteorologists developed the Humidex in response to a desire to come up with a formula which could more accurately express the way the temperature felt, combining the factors of heat and humidity.

As you may have noted, when the weather is humid, it feels much warmer. This is because the humidity makes it difficult for sweat to evaporate from the body, which makes it harder to cool down. The accumulated sweat may also leave people feeling slick or sticky, increasing their discomfort. Residents of notoriously humid areas often have to take steps in warm weather to ensure that they stay healthy and comfortable, such as using dehumidifies and fans in their homes.

Humidex combines the temperature and humidity to create the perceived temperature.
Humidex combines the temperature and humidity to create the perceived temperature.

The formula used to derive the Humidex is a bit complex, but essentially it combines the dew point and measured temperature. A Humidex of 40, which would be equivalent to 104 degrees Fahrenheit, is considered “uncomfortable.” When the Humidex hits 45 (113 Fahrenheit), it starts to become dangerous, and at 54 (almost 130 degrees Fahrenheit), heat stroke is imminent. Recordings in the 50s are relatively rare.

The Humidex can be a more accurate way to calculate how the weather will feel on any given day than considering the temperature alone.
The Humidex can be a more accurate way to calculate how the weather will feel on any given day than considering the temperature alone.

As a general rule, people ignore the Humidex when it is below 30 (equivalent to 86 degrees Fahrenheit), because this temperature is viewed as safe for most people. It is only when the Humidex starts to creep towards 40 that people may begin to be concerned. Numbers above 45 may result in high temperature warnings, alerting people to the danger so that they can adjust their lives accordingly until the temperatures cool down.

People should become concerned when the humidex approaches 40, as they risk heat disorders if exposed for long periods of time.
People should become concerned when the humidex approaches 40, as they risk heat disorders if exposed for long periods of time.

The Humidex debuted in 1965 in Canada, and has since spread to other regions of the world. This useful measure can be a useful rule of thumb for quickly assessing weather conditions to determine whether or not they are potentially hazardous. Looking at temperature predictions alone, it is sometimes possible to miss potentially dangerous weather, which could result in a variety of health problems associated with higher temperatures.

Frequently Asked Questions

What exactly is Humidex and how is it calculated?

Humidex, short for humidity index, is a Canadian innovation that combines air temperature and humidity to reflect the perceived temperature. It's calculated using a formula that incorporates the dew point temperature to assess human discomfort due to combined heat and high moisture levels. The higher the Humidex, the more uncomfortable you're likely to feel.

Why is Humidex important to consider in daily weather forecasts?

Humidex is crucial because it provides a more accurate representation of how hot it feels, rather than just the actual air temperature. This is particularly important for public health and safety, as high Humidex values can lead to heat stress and heat-related illnesses. It helps individuals plan their activities and take precautions during hot and humid conditions.

How does Humidex differ from the "feels like" temperature or Heat Index?

While Humidex is specifically used in Canada, the "feels like" temperature or Heat Index is commonly used in the United States. Both indices aim to describe how hot it feels by considering temperature and humidity, but they use different formulas. The Heat Index also factors in wind speed and solar radiation, providing a slightly different comfort measure.

At what Humidex level does the weather become dangerous?

When the Humidex reaches 30, it indicates discomfort, while a reading of 40 or above signifies dangerous heat levels, potentially leading to heat stroke if proper precautions are not taken. According to Environment Canada, a Humidex of 45 is considered extremely high, and such conditions warrant public warnings due to the risk of heat-related illnesses.

Can Humidex values affect outdoor activities and how should one prepare?

High Humidex values can significantly impact outdoor activities by increasing the risk of heat exhaustion and dehydration. It's advisable to schedule strenuous activities during cooler parts of the day, stay hydrated, wear light clothing, and take frequent breaks in shaded or air-conditioned areas to mitigate the effects of high Humidex readings.

Is the Humidex scale used internationally?

The Humidex scale is primarily used in Canada. Other countries have their own indices, such as the Heat Index in the United States and the Apparent Temperature in Australia. Each index is tailored to regional climatic conditions and serves a similar purpose: to inform the public about the potential impact of heat and humidity on health and comfort.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

Discussion Comments

anon1004548

Great explanation, Mary.

I am just wondering, if the Humidex scale was developed in 1965 by Canadian meteorologists, how can a Canadian company from 1989 have it as registered trade mark?

That is not only very confusing, but does it mean one has to include a small r every time the Humidex index is discussed?

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    • Humidex combines the temperature and humidity to create the perceived temperature.
      By: fpdress
      Humidex combines the temperature and humidity to create the perceived temperature.
    • The Humidex can be a more accurate way to calculate how the weather will feel on any given day than considering the temperature alone.
      By: Silkstock
      The Humidex can be a more accurate way to calculate how the weather will feel on any given day than considering the temperature alone.
    • People should become concerned when the humidex approaches 40, as they risk heat disorders if exposed for long periods of time.
      By: Maridav
      People should become concerned when the humidex approaches 40, as they risk heat disorders if exposed for long periods of time.