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
Cloud cover
Total cloud cover (%)
CO
Carbon monoxide concentration in the air (µg/m3)
Coastal zone
Portion of the coastline about 50 nautical miles long, extending up to 10 nautical miles from the coast.Particularly suitable for coastal sailing and usually for day sailing.They are proposed for Europe, the Mediterranean and the Lesser Antilles.
Cold front
Boundary between a warm air mass and a cold air mass. Cold air behind the front replaces warm air. This front is associated with a sudden deterioration in the weather (clouds, precipitation and wind). It is represented on frontology maps by a blue line with triangles.
D
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)
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).
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)
Fresh Snow
Recent snow still composed of recognizable particles.
G
Gusts of wind (10 m)
Gusts of wind are sudden, abrupt variations in instantaneous wind speed
10 m above ground.
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”
Occluded front / occlusion
Boundary that forms when a cold front catches up with a warm front, with the warm sector being pushed aloft. It is associated with gloomy weather with precipitation which is heaviest near the center of the depression. It is represented on frontology maps by a purple line with alternating triangles and semicircles.
Offshore sea
Significant height of total wave height offshore, combining wind sea and swell (in m)
Offshore wind
Offshore wind average speed (km/h)
Offshore zone
A stretch of sea or ocean 150 to 200 nautical miles long, extending from 10 miles to about 100 miles from the coast.More suitable for offshore sailing and longer crossings (one to several days).They are proposed for the Atlantic, the Mediterranean and the Caribbean
Open sea zone
A stretch of sea or ocean approximately 250 nautical miles in length and width encompassing the so-called high seas or international waters.Intended for very long crossings (e.g. from continent to continent, over one or more weeks).
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
Stationary front
Boundary between two air masses with different characteristics which slide past each other without any interaction. The stationary front tends to stagnate for several days in the same area.
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)
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
Warm front
Boundary between a warm air mass and a cold air mass. Warm air behind the front replaces cold air. This front is associated with a progressive deterioration of the weather (high-altitude clouds then precipitation). It is represented on frontology maps by a red line with semi-circles.
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)
* Parameter available for METEO PRO and METEO PRO+ data
