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Wind

Wind direction

The arrow indicates wind direction:

: North wind (from north to south).
: South wind (from south to north).
: West wind (from west to east).
: East wind (from east to west).

Wind speed

Measured in meters per second (m/s) using an anemometer.

Yandex Weather displays the wind speed at the height of 10 meters above the ground.

Wind speed is affected by:

Different atmospheric pressure and temperature in various parts of the atmosphere.
Uneven heating of the underlying surface.
Terrain features (mountain, forest, or city).


Wind speed, m/s	Wind force
0	Calm
1–5	Light
6–10	Moderate
more than 10	Strong

You can find a more detailed breakdown of wind speeds on the Beaufort scale. This is an international scale for measuring wind speed on land and at sea.

Note. In the web version of Yandex Weather, you can view the average wind speed. In the mobile version, you can see both the average and maximum wind speeds during gusts (in the detailed forecast).

Weather phenomena

To find out what the weather is going to be like, use the following icon descriptions. Icons with a sun mean daytime, and those with a crescent moon mean nighttime. Icons without a sun or crescent moon mean any time of day.


Icon	Description
/	Clear
	Fog
/	Partly cloudy
	Overcast
/	Light rain
/	Light rain
	Rain
	Rain
	Thunderstorm
	Thunderstorm with rain
/	Shower
	Shower
	Hail
	Sleet
/	Light snow
	Light snow
/	Light snow
	Snow
	Snow

Humidity

Shows the amount of water vapor in the air. Humidity is measured 2 m above ground.

High humidity increases the likelihood of dew or fog.

Humidity is affected by processes that depend on terrain features:

Moisture transfer by air flows.
Water evaporation.

The forecast shows the relative humidity of the air, i.e. the amount of water vapor in the air as compared with the maximum amount of water that the air could possibly hold at the current temperature.

Humidity is shown in the weather card on the service's homepage and in the detailed forecast.

Pressure

Pressure is affected by atmospheric circulation.

When a cyclone is coming, the atmospheric pressure decreases, and when an anti-cyclone is, it increases.

To determine the type of atmospheric circulation, open the Wind tab on the weather maps and check the direction of the air flows above your city:

Counterclockwise means a cyclone.
Clockwise means an anticyclone.

Note. In the Southern hemisphere, the cyclone makes the air rotate clockwise, and the anti-cyclone makes it go counterclockwise.

Most people are accustomed to the pressure of 760 mmHg. But the normal atmospheric pressure for each person depends on the region they live in, while the pressure of the region depends on the terrain altitude. For example, in Vienna, the average altitude is 151 m and the standard pressure for it is 744 mmHg. That's why people from Vienna would consider the pressure of 760 mmHg to be increased.


Difference from the norm for the region, mmHg	Pressure value
More than 20 below the norm for the region	Low
10–20 lower than the norm for the region	Reduced
Within 10 above the norm for the region	Standard
10–20 higher than the norm for the region	Increased
More than 20 above the norm for the region	High


Difference from the norm for the region, mmHg	Pressure value
More than 20 below the norm for the region	Low
10–20 lower than the norm for the region	Reduced
Within 10 above the norm for the region	Standard
10–20 higher than the norm for the region	Increased
More than 20 above the norm for the region	High

Magnetic field

The magnetic field is affected by the solar activity. When solar flares occur, a stream of particles reaches the Earth and impacts its magnetic field.

Researchers measure the state of the magnetic field with the Kp index. It shows the average deviation of the entire Earth's magnetic field from the norm calculated for three-hour intervals. The Kp index values range from 1 (quiet activity) to 10 (extreme magnetic storm).

In the service, the values of the Kp index correspond to the following verbal definitions:


Kp index	Field state in the service
Less than 4	Quiet
4	Unstable
5	Slightly disturbed
6	Disturbed
7	Magnetic storm
8 or higher	Strong magnetic storm

You can view the state of the magnetic field in the detailed forecast. Yandex Weather shows the state of the magnetic field for today and the next three days. No forecast is made for subsequent days, as its accuracy is low.

Magnetic field disturbances may cause a communication blackout and power system failures. Some people may be affected by the force of a magnetic storm.

Feels like

The same temperature values can be perceived differently, depending on humidity, wind force, and other factors. For example, a temperature of –5 °C feels colder when there's also a strong wind, and a temperature of +25 °C feels hotter when there's also high humidity and bright sunshine. Because of that, the forecast shows the indicator Feels like. It shows how comfortable the weather conditions are.

When calculating the “feels like” temperature, the following is taken into account:

Air temperature.
Humidity.
Wind speed.
Solar radiation.

Note. The “feels like” temperature is calculated as an average for most people. Everyone perceives temperature differently, so you might disagree with the Feels like indicator.

Daylight hours

The period from sunrise to sunset .

Yandex Weather calculates the duration of daylight taking into account atmospheric refraction. This phenomenon is about the bending and scattering of sunlight. When the light passes from the more dense layers of the atmosphere to the less dense ones (and vice versa), its speed changes and the sun rays deviate from a straight line. Atmospheric refraction is especially noticeable when the sun is near the horizon: when it is already below the horizon, you can still see the sun's disk.

Daylight duration increases due to atmospheric refraction.

In the full version

On the service's home page and in the detailed forecast. The daylight duration is also shown there.

In the mobile version

On the main page of the “Gardening” section.

In the Yandex Weather app

In the hourly forecast and in the detailed day forecast at the bottom of the page. The daylight duration is shown in the detailed forecast.

Water temperature

Shows water surface temperature.

The water temperature is only displayed for cities located near large water bodies. If the nearest weather stations to the city don't measure water temperature, Yandex Weather calculates this indicator.

You can see the water temperature on the main page of the service in the hourly forecast card and in the detailed forecast.

Air temperature

Shows the temperature at 2 m above the ground.

Calculations take into account the data received from weather stations which have special conditions for measuring air temperature:

Located at a height of 2 m from the ground.
Open to the wind.
Not affected by direct sunlight.

Home thermometers aren't always installed according to the same rules, so their readings might differ from the temperature on Yandex Weather.

UV index

Describes the level of solar radiation at the surface of the Earth and whether it's dangerous to humans.

The index value depends on the following parameters:

Seasonal activity of the sun.
The sun's position relative to the latitude, horizon, and sea level.
The condition of the ozone layer above the area.
Aerosol concentration in the air.
Terrain reflectivity.
Type of clouds.

Note. Most often, in cloudy and rainy weather, the UV index is low, while in a fog, the solar radiation is repeatedly reflected and dispersed, and the UV index increases. This effect is often visible in the mountains.

How to protect yourself from solar radiation


UV index value	WHO recommendations
0–2: low	There is minimal risk of sunburn, even if your skin is sensitive.
3–7: moderate	Try to stay in the shade from 12:00 to 16:00. Use sunscreen with SPF 15–30. Wear a hat and a long-sleeve shirt.
More than 8: very high	Avoid being outside from 12:00 to 16:00. Use 50 SPF sunscreen. Wear protective clothing and sunglasses.


UV index value	WHO recommendations
0–2: low	There is minimal risk of sunburn, even if your skin is sensitive.
3–7: moderate	Try to stay in the shade from 12:00 to 16:00. Use sunscreen with SPF 15–30. Wear a hat and a long-sleeve shirt.
More than 8: very high	Avoid being outside from 12:00 to 16:00. Use 50 SPF sunscreen. Wear protective clothing and sunglasses.

Where to find the UV index

The current UV index is shown on the service's homepage.

You can find the UV index for the next 4 days in the detailed forecast.

Moon phase

Shows how much the moon is illuminated by the sun.

On the service's homepage, in the forecast for today, you can see textual information about the phase of the moon.

In the detailed 10-day forecast, the phase of the moon is displayed as an image. The yellow portion of the disk shows the visible part of the Moon, while the dark gray one reflects its invisible part.


Icon	Moon phase	Approximate time when the moon is visible in the sky
	New moon	Not visible
	Waxing gibbous	09:00–21:00
	First quarter	12:00–00:00
	Waxing gibbous	15:00–03:00
	Full moon	18:00–06:00
	Waning crescent	21:00–09:00
	Last quarter	00:00–12:00
	Waning crescent	03:00–15:00


Icon	Moon phase	Approximate time when the moon is visible in the sky
	New moon	Not visible
	Waxing gibbous	09:00–21:00
	First quarter	12:00–00:00
	Waxing gibbous	15:00–03:00
	Full moon	18:00–06:00
	Waning crescent	21:00–09:00
	Last quarter	00:00–12:00
	Waning crescent	03:00–15:00

How Yandex Weather calculates the moon phase

The service uses the method described by Jean Meeus in his book “Astronomical Algorithms” which is based on the calculation of the Sun's illumination factor of the Moon's disk. This factor depends on the selenocentric distance of the Earth from the Sun (phase angle).

When calculating the phase angle, the distances from the Earth to the Sun and from the Earth to the Moon are taken into account, as are the longitude and latitude of the lunar subsolar point.

Depending on the day of the sidereal month (the period during which the Moon makes a complete revolution around the Earth), the distance from the Earth to the Moon and from the Earth to the Sun varies. The distance from the Earth to the Sun is considered to be equal to one astronomical unit (1 AU), which is 149,971,520 km, while the distance from the Earth to the Moon and the longitude and latitude of the lunar subsolar point are calculated for certain dates and times.

The illumination factor can take values from 0 to 1:

0 — New moon.
0.5 — First or last quarter.
1 — Full moon.

You can determine whether the Moon is growing or waning by calculating the factor for two days. If it increases for the following day, the Moon is waxing; otherwise, the Moon is waning.

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