Weather Data Documentation

The Visual Crossing Weather Data platform provides the ability to easily access weather data sets including weather forecast data, weather history data and historical weather summary data. The data is available for download through the Weather Data Query Page and the Timeline Weather API.

Core weather columns

These columns are common to most weather data sets unless disabled. Advanced weather elements are also available including agricultural and energy elements.

Element	Description	US	metric	UK
tempmax	Maximum Temperature	F	C	C
tempmin	Minimum Temperature	F	C	C
temp	Temperature (or mean temperature)	F	C	C
dew	Dew Point	F	C	C
feelslike	Feels like	F	C	C
precip	Precipitation	inches	mm	mm
precipprob	Precipitation chance	%	%	%
precipcover	Precipitation cover	%	%	%
preciptype	Precipitation type	–	–	–
snow	Snow	inches	cm	cm
snowdepth	Snow depth	inches	cm	cm
windspeed	Wind speed	mph	kph	mph
windgust	Wind gust	mph	kph	mph
winddir	Wind direction	degrees	degrees	degrees
visibility	Visibility	miles	km	miles
cloudcover	Cloud cover	%	%	%
humidity	Relative humidity	%	%	%
pressure	Sea level pressure	mb	mb	mb
solarradiation	Solar radiation	W/m2	W/m2	W/m2
solarenergy	Solar energy	MJ/m2	MJ/m2	MJ/m2
uvindex	UV index	–	–	–
severerisk	Severe Risk	–	–	–
sunrise	Sunrise time	–	–	–
sunset	Sunset time	–	–	–
moonphase	Moonphase	–	–	–
icon	A weather icon	–	–	–
conditions	Short text about the weather	–	–	–
description	Description of the weather for the day	–	–	–
stations	List of weather stations sources	–	–	–

Temperature (temp, tempmax, tempmin)

There are three main columns for indicating temperature – Minimum Temperature, Maximum Temperature and Temperature. These will return data in Fahrenheit, Celsius or Kelvin depending on the unit group. The three temperature columns indicate the minimum, maximum and average (mean) temperature for the time period in question. For example, if you request daily data then you will receive the data for minimum, maximum and mean temperature for each day. If you request data for the shortest available timeframe for that request (typically one hour), the minimum, maximum and mean are returned with the same value. All data sets will include all three columns even if the values are the same to ease consumption of the data sets and keep data set consistency.

Wind (wspd, wdir, wgust)

Wind data includes wind speed, wind gust and wind direction.

Wind speed and wind direction (wspd, wdir)

The wind speed and wind direction indicate the wind speed for the location and time period requested. The hourly speed and direction values are the average (mean) of the speed and direction for the two minutes prior to the measurement being record. Daily and other time period values display the maximum of the hourly values. In the Timeline Weather API, the mean and minimum daily windspeed values are also available.

The units of the data will be in miles per hour, kilometers per hour or m/s depending on the unit group.

Wind speed is typically measured 10m above ground in a location with no nearby obstructions.

The wind direction indicates the direction from where the wind is blowing from. The units of the wind direction is degrees from north. The value ranges from 0 degrees (from the North), to 90 degrees (from the east), 180 degrees (from the south), 270 (from the west) back to 360 degrees.

Wind gust (wgust)

Wind gust is the maximum wind speed measures over a short amount of time (typically less than 20 seconds). Note that a wind gust requires the measured short term wind speed to be significantly more than mean wind speed. Typically, the wind speed should be 10 knots more (11mph or 18kph). When the wind gust does not meet these criteria, a null/empty value is returned.

The wind direction indicates the direction from where the wind is blowing from. The units of the wind direction is degrees from north. The value ranges from 0 degrees (from the North), to 90 degrees (from the east), 180 degrees (from the south), 270 (from the west) back to 360 degrees.

Precipitation (precip, precipchance and precipcover)

Precipitation is the sum of the amount of liquid equivalent rainfall, snow or other precipitation that fell is predicted to fall in the period. Three output variables cover precipitation:

Precipitation (precip)

The amount of precipitation that fell or is predicted to fall in the specified time period. The values are indicated in inches or mm.

Chance of precipitation (precipchance)

The possibility of precipitation for the given time period expressed as a percentage change from 0-100%. This applies to the forecast queries only.

Precipitation Coverage

This is the proportion of time for which measurable precipitation was recorded during the time period, expressed as a percentage. For example, if within a 24 hour day there are six hours of measurable rainfall, the precipitation coverage is 25% (6/24*100). This information is only available for historical weather observation data and historical summaries. Note that where as trace precipitation is considered zero value for the precipitation column, a trace precipitation report will be considered as precipitation for the precipitation coverage column. Therefore it is possible to observe zero reported precipitation with a non-zero precipitation coverage.

Precipitation Type (preciptype )

(Forecast only) Provides the type(s) of precipitation expected. Possible values include rain, snow, freezing rain and ice.

Cloud cover (cloudcover)

Cloud cover is the amount of sky that is covered by cloud expressed as a percentage. The cloud coverage is for all altitudes. Daily values include the mean of the hourly cloud coverage values.

Snow and Snow Depth (snow, snowdepth)

Snow is the amount of new snow that has fallen in the time period. Snow depth is the average amount of snow currently on the ground for the time period. Snow depth will increase with additional snowfall and decrease with melting and compaction. Both snow and snow depth are expressed in inches or centimeters.

Relative Humidity, Feelslike, Heat Index and Wind Chill (humidity, heatindex, windchill)

Relative humidity (humidity)

Relative humidity is the amount of water vapor present in the air compared the maximum amount possible for a given temperature, expressed as a mean percentage. Human comfort levels are typically found between 30-70%. Values higher than 70% are considered humid. Values lower than 30% are considered dry.

Feelslike, Heat Index and Wind chill

Heat Index is a measure of how hot it feels combining the actual air temperature with the relative humidity. High humidity is associated with discomfort by making the apparent temperature hotter than it would otherwise feel. Values are expressed in the same units as temperature. Heat index values are only calculated when the temperature is greater than 80F (about 26.7C) and the relative humidity is greater than 40%. An empty value is returned outside of these ranges.

Wind chill is the measure of how cold it feels combining the actual air temperature with the wind speed. Wind makes temperatures feel colder than when the air is still. Values are expressed in the same units as temperature. Wind chill values are only calculated when the temperature is less than 50F (about 10C) and the wind speed is greater than 3mph (5kph). An empty value is returned outside of these ranges.

Temperature, heat index and wind chill are combined into a single ‘feelslike’ element for clarity and ease of use. The daily maximum (feelslikemax) and minimum (feelslikemin) are included in daily values. See What is the difference between temperature, heat index, wind chill, feels like temperature, apparent temperature and RealFeel Temperature? for more information.

Visibility

Visibility is the distance that can be seen in daylight. This accounts for weather phenomenon such as haze, mist, fog or smoke. The distance is expressed in miles or kilometers.

Sea Level Pressure (sealevelpressure)

The atmospheric pressure at a location that removes reduction in pressure due to the altitude of the location. This is expressed in millibars.

Solar radiation and energy

Solar radiation and solar energy are available in the forecast and historical observations datasets. The solar radiation measures the power (in W/m²) at the instantaneous moment of the observation (or forecast prediction). The solar energy (in MJ/m² ) indicates the total energy from the sun that builds up over an hour or day. See the full solar radiation data documentation.

UV Index

A value between 0 and 10 indicating the level of ultra violet (UV) exposure for that hour or day. 10 represents high level of exposure, and 0 represents no exposure. The UV index is calculated based on amount of short wave solar radiation which in turn is a level the cloudiness, type of cloud, time of day, time of year and location altitude. Daily values represent the maximum value of the hourly values.

Severe Weather (CAPE, CIN, severe risk)

Severe risk is value between 0 and 100 representing the risk of convective storms (e.g. thunderstorms, hail and tornadoes). Severe risk is a scaled measure that combines a variety of other fields such as the convective available potential energy (CAPE) and convective inhibition (CIN), predicted rain and wind. Typically, a severe risk value less than 30 indicates a low risk, between 30 and 70 a moderate risk and above 70 a high risk.

CAPE – convective available potential energy. This is a numbering indicating amount of energy available to produce thunderstorms. A higher values indicates a more unstable atmosphere capable of creating stronger storms. Values lower than 1000 J/kg indicate generally low instability, between 1000-2500 J/kg medium instability and 2500-4000 J/kg high instability. Values greater than 4000 J/kg indicating an extremely unstable atmosphere.

CIN – convective inhibition. A number representing the level of atmospheric tendency to prevent instability and therefore prevent thunderstorms.

Weather Type (conditions)

Notable weather conditions reported at a particular location such as any thunderstorms, rainfall etc. The availability of this data is dependent on the weather station that observed the information and is not reported by all weather stations – the absence of a particular weather type should not be considered evidence that the weather type did not occur. Weather type is only available for historical datasets and relies on the weather stations providing the data.

See Weather Data Conditions for more information.

Astronomical information

Sunset & sunrise

The time of the sunrise and sunset for the date and location in question. Times are given in the local time zone.

Moonphase

A decimal value representing the current moon phase between 0 and 1 where 0 represents the new moon, 0.5 represents the full moon. The full cycle can be represented as:

• 0 – new moon
• 0-0.25 – waxing crescent
• 0.25 – first quarter
• 0.25-0.5 – waxing gibbous
• 0.5 – full moon
• 0.5-0.75 – waning gibbous
• 0.75 – last quarter
• 0.75 -1 – waning crescent

Icons

The icon field holds a text value that users can use to indicate which icon to show when displaying the weather data. For more information, and sample icons sets, please see Defining the icon set parameter in the Weather API.

Descriptions and language support

The text descriptions that are included can be returned in different languages using the ‘lang’ API parameter.

For more information, please see the Timeline Weather API documentations and How to create or modify language files.

Contributing Stations

For historical observations, indicates the weather stations that were used for creating the observation. This is a list of weather station names, their ID within the Visual Crossing weather data platform and the distance from the requested location to the weather station. For more information on how weather station data is combined, please read more.

General weather data structure

We aim to keep the data set structure as consistent as possible between the three main categories of data – weather forecast, historical weather observations and historical weather summaries. This allows you to easily switch between using data for weather forecast and historical records within the same data and can be useful in many applications. All the data sets include the following characteristics:

Data Set Structure

All data sets are a simple table structure which is available in multiple formats including plain text delimited such as CSV, JSON and ODATA. The data includes a single row of headers information indicating the information in the column. These column headers will either be in a human readable header that may be translated or in a single, short form which is not translated. The short form is typically used for Weather API usage to make it easier to consume the data. When using the Weather API, the shortColumnNames parameters indicates whether or not short column names will be used.

Hourly and Daily Dataset Aggregation

All data within the a system is calculated at the hourly data level for accuracy and consistency. When requests are made for longer time periods, such as daily weather forecast or monthly historical summaries, the hourly data is aggregated using average (mean), sum, minimum or maximum functions. The individual column documentation below explains the aggregation method used.

Unit group

The units of the data are specified by the overall unit group requests such as metric, US units etc. This unit group defines the unit of measure used for each column type – all columns of the same variable type will have the same unit. For example, Celsius will be used for all temperature related quantities when the unit group is set to metric.

Common columns

Data sets will typically include information about the location, period or data time. If the requested data includes address, the address information is included in the return value. In addition, the latitude and longitude of the requested locations are returned using decimals degrees. The longitude value are zero based at the prime meridian. Values west of the prime meridian are negative and east are positive.

For more information on how dates and times are returned in the Weather API results, see Dates and Times in the Weather API.

Empty values

Empty values (or null values) are used within the data set to indicate an absence of data, such as missing weather information or unknown data. They are not used to indicate a zero value. For example, an unknown precipitation value will be marked as empty or null. A zero amount of precipitation will be indicated by the value zero.

Weather element availability

We aim to include all weather elements such as temperature, wind, precipitation etc. for all locations. Unfortunately not all locations report all weather elements. In those cases the columns will be included in the data but include null values. We continue to expand the availability of weather elements as we add additional data sets and data processing.

Questions or need help?

If you have a question or need help, please post on our actively monitored forum for the fastest replies. You can also contact us via our support site or drop us an email at support@visualcrossing.com.