Meteorological Methodology & Formulas

WeatherCA is engineered according to the official equations established by Environment Canada, the Meteorological Service of Canada (MSC), and Health Canada.

1. Canadian Wind Chill Index (T_wc)

Introduced in 2001 by Environment Canada in cooperation with the US National Weather Service, the modern Wind Chill formula calculates convective heat loss from human skin based on wind speed measured at standard anemometer height (10 meters aloft):

T_wc = 13.12 + 0.6215 * T_air - 11.37 * (V_10)^0.16 + 0.3965 * T_air * (V_10)^0.16

• T_air = Air temperature in degrees Celsius (°C)

• V_10 = Wind speed in kilometers per hour (km/h) measured at 10 meters

Frostbite Threshold Timelines

-28 to -39 Wind Chill

Risk of frostbite within 10 to 30 minutes

-40 to -47 Wind Chill

Frostbite occurs within 5 to 10 minutes

-48 and Below

Severe danger: skin freezes in under 2 to 5 minutes

2. Canadian Humidex (H)

Developed in 1965 by Canadian meteorologists J.M. Masterton and F.A. Richardson, the Humidex is a dimensionless index indicating perceived summer warmth by incorporating atmospheric vapor pressure:

Humidex = T_air + (5 / 9) * (e - 10)

Where vapor pressure e (in millibars / hPa) is derived from the dew point temperature:

e = 6.11 * 10 ^ ((7.5 * T_dew) / (237.3 + T_dew))

3. Air Quality Health Index (AQHI)

Canada’s AQHI differs from the US AQI by measuring the combined multi-pollutant health risk from ozone (O3), fine particulate matter (PM2.5), and nitrogen dioxide (NO2) based on excess mortality epidemiology:

AQHI = (10 / 10.4) * 100 * [ (exp(0.000871 * NO2) - 1) + (exp(0.000537 * O3) - 1) + (exp(0.000487 * PM2.5) - 1) ]