A

Accumulation of precipitations*
Total amount of rain falling in x hours (between 0H and 23h59) in mm

Air quality index (AQI)
European air quality index which includes 6 levels (from 0-50 good to 301-500 dangerous)

Air quality index (ATMO)
French air quality index which includes 6 levels (from 1 good to 6 extremely bad)

Air quality index (CAQI)
American air quality index which includes 5 levels (from 0-25 good to 301-500 very bad)

Allergy risk index
Index which establishes, on a scale of 1 to 5, the allergy risk, taking into account the different types of pollen and the air quality

Amount of precipitations
Amount of precipitations (rain, snow, hail...) falling in 1 hour (mm)

C

CO
Carbon monoxide concentration in the air (µg/m3)

Cloud cover
Total cloud cover (%)

D

DJU (Unified Degree Day)*
This is the difference between the outside temperature and a reference temperature which makes it possible to make estimates of thermal energy consumption to keep a building comfortable in proportion to the severity of winter or the heat of the summer (°C).

Dew point temperature*
This is the temperature at which air must be cooled in order for the water vapour it contains to condense into dew or rime ice (°C)

Dust
Dust concentration in the air (µg/m3)

F

Felt temperature
Felt temperature is calculated using the air temperature, and integrating wind, humidity and sunshine (°C)

G

Gusts of wind (10 m)
Gusts of wind are sudden, abrupt variations in instantaneous wind speed 10 m above ground. Gust speed is displayed in our forecasts only when the difference with average wind speed is above or equal to 5 knots (about 9 km/h).

H

High cloud*
High altitude cloud cover (beyond 6,000 m) in %

Humidex*
This is a comfort index calculated using the air temperature and integrating relative humidity. It ranges from under 30 which corresponds to no felt discomfort, to over 54 for impending heat stroke

Humidity
Water vapour quantity in the air 2 metres high (%)

L

Low cloud*
Low altitude cloud cover (up to 2,000 m) in %

Luminosity index*
Technical parameter indicating the forecast luminosity compared to the maximum luminosity possible at a given location

Luminous flow*
Quantity of visible light received on the surface of Earth, in lumen (lm)

M

Medium cloud*
Medium altitude cloud cover (between 2,000 and 6,000 m) in %

Medium wind (10 m)
Average wind speed 10 metres above ground

N

NO2
Nitrogen dioxide concentration in the air (µg/m3)

O

O3
Concentration in tropospheric ozone (µg/m3), i.e. ground level ozone located in the troposphere (between 0 and 10 km altitude), not to be confused with stratospheric ozone (over 10 km altitude) which is famous for the phenomenon known as the “Ozone hole”

Offshore sea
Significant height of total wave height offshore, combining wind sea and swell (in m)

Offshore wind
Offshore wind average speed (km/h)

P

PET (Potential Evapotranspiration)*
This is the emission of water vapour caused by soil and vegetation cover transpiration (in mm/h). It depends on soil surface, air temperature, sunshine and wind.

PM10
Concentration in fine particles 10 µm and smaller in the air (µg/m3)

PM2.5
Concentration in fine particles 2.5 µm and smaller in the air (µg/m3)

Pollen - Mugwort
Mugwort pollen concentration in the air (in µg/m3)

Pollens - Alder
Alder pollen concentration in the air (in µg/m3)

Pollens - Ambrosia
Ambrosia pollen concentration in the air (in µg/m3)

Pollens - Birch
Birch pollen concentration in the air (in µg/m3)

Pollens - Grasses
Grass pollen concentration in the air (in µg/m3)

Pollens - Olive tree
Polive tree pollen concentration in the air (in µg/m3)

Pressure
Calculation of the atmospheric pressure at sea level, making it possible to compare ground-level atmospheric pressures whatever the altitude of the considered location (hPa)

R

Rain/snow line
Elevation at which precipitation type transitions from rain to snow (m)

Risk of fog*
Fog probability, in %

Risk of precipitations
Precipitation probability, in %

Risk of rain*
Rain probability, in %

Risk of snow*
Snowfall probability, in %

Risk of thunderstorm*
Thunderstorm probability, in %

S

SO2
Sulphur dioxide concentration in the air (µg/m3)

Soil temperature*
Temperature measured at ground surface (°C)

Speed at altitude (20m)*
Average wind speed 20 metres above ground

Speed at altitude (50m)*
Average wind speed 50 metres above ground

Sunshine*
Number of hours during which the sun can be seen, depends on the cloud cover. For example: 100% cloud cover over one hour amounts to 0h sunshine, 50% cloud cover amounts to 0.5h sunshine

Swell height
Primary swell wave height (m)

Swell period
Time between two swell crests (in seconds)

T

Temperature
Air temperature 2 metres high under shelter (°C)

Tidal current
Direction and speed of currents only generated by tide (in ° and m/s)

Tide height
Sea level height compared to the theoretical height without the influence of tide (hydrographic level)

Total wave height
height estimate (trough to crest) of the expected highest individual wave, resulting from the concentrated energy of several waves into a single one whose height is significantly higher than the significant wave height (m). However, the value indicated on our website does not take into account rogue waves, which are unpredictable and whose height can be well over twice the significant wave height.

Total wave height or significant wave height
average height (trough to crest) of the highest third of the waves created by wind and swell. This value is close to an observer’s visual estimate (m)

Type of precipitations
Rain, freezing rain, rain and snow mixed, snow, hail, ice pellets

U

UV
Index used to evaluate ultraviolet solar radiation which includes 5 levels (from 0-2 low to >11 extreme)

V

Visibility
Visibility 2 metres high from the ground (in m or km)

W

Wave length
Wave length associated with total wave height, meaning the distance between 2 crests (m)

Wind sea
Height of waves generated by the wind (m)

Z

Zero degree isotherm
Altitude in which air temperature is at 0°C (m)
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