Cloudiness is a number of clouds observed in a certain place. It is measured in percentage. Nil cloudiness means that the sky is cloudless. 100% cloudiness corresponds to the sky totally covered with clouds. 30% cloudiness means that 30% of the sky is covered with clouds.
Precipitation is the layer thickness of precipitated water, ACCUMULATED between the nearest time points indicated in the table. For example, between 10:00 and 16:00 or between 16:00 and 22:00, etc. Please pay attention that the amount of precipitation is the amount of water. It means precipitation in solid state (snow, sleet, snow grains, hail) is calculated as the corresponding amount of water. Note also that if the values of other parameters of weather (clouds, pressure, temperature, humidity and wind) refer to the MOMENT of time, precipitation belongs to the PERIOD of time between the nearest time points.To convert liquid precipitation into approximate snow depth, the ratio of 1:10 is used. For example, 1 mm of precipitation in the form of water is approximately equivalent to a 10mm depth of newly fallen snow.
Pressure is atmospheric pressure near the ground. At the sea level the average pressure is close to 760 mmHg. Deviation of pressure from the average pressure is associated with cyclonic / anticyclonic activity. In a cyclone pressure decreases and in an anticyclone it increases. The average pressure in any location is very dependent on height of the ground relative to the sea level. With increasing altitude the pressure decreases. For example, in case of the same state of the atmosphere, the atmospheric pressure in Moscow and St. Petersburg will differ due to the fact that these cities are located at different altitudes. In Moscow, at an altitude of about 156 m above the sea level, the pressure will be approximately by 15 mmHg. lower than in St. Petersburg, located at a height of about 4 m above the sea level.
Humidity is relative humidity at a height of 1.5 m. It is measured in percentage. Relative humidity is the ratio of actual absolute humidity to absolute humidity for the state of saturation at the same temperature. In its turn, the absolute humidity is the density of water vapor in the air, expressed as the number of grams of water in one cubic meter of air. Thus, the less the air is saturated with water vapor, the lower its relative humidity is. The lower the relative humidity, the drier the air feels. And the higher the relative humidity, the wetter or damper the air is.
Wind is wind direction and velocity at a height of 10 m. Direction indicates where the wind is blowing from. For example, the north wind blows from the north, the south one blows from the south. The symbols of wind direction: N - north, NE - north-east, E - east, SE - south-east, etc.
The relation between wind speed, description and land conditions is presented on the Beaufort scale.
The Moon passes through the following phases of illumination:
New Moon is a state when the Moon is not visible,
First quarter moon is a state when half of the Moon is visible,
Full Moon is a state when the Moon is fully visible,
Last quarter moon is a state when half of the Moon is visible again.
For more information see FAQ