What historical weather measures are available?

When you are exploring historical weather data for business and personal use, it is important to know what weather measures are available. In this article we’ll provide a overview of the available weather metrics (also known as weather variables and weather parameters) grouped by theme. In addition, we’ll supply links to more detailed information where so that you can do more in-depth learning. The ultimate source of this information, the full documentation, is also available for your edification as well.

Overview of available weather measures

— Temperature Average (mean) temperature during the period
— Minimum TemperatureMinimum temperature during the period
— Maximum Temperature Maximum temperature during the period
— PrecipitationTotal amount of rain, snow, etc. converted to liquid
— Precipitation Coverage The proportion of hours where there was non-zero precipitation
— SnowSnow that fell during the period
— Snow DepthDepth of snow on the ground
— HailSolid precipitation the fell during the period
— Wind SpeedWind speed at the time of the report
— Wind DirectionWind direction at the time of the report
— Wind GustMaximum very short-term wind speed
Clouds and Visibility
— VisibilityHorizontal visibility
— Cloud coverPercentage of sky obscured by clouds
“Feels like”
— Heat IndexBodily discomfort related to hot temperature & humidity
— Wind ChillBodily discomfort related to cold temperature & wind
— SunriseTime at which the sun rises
— SunsetTime at which the sun sets
— Moon PhaseCurrent phase of the moon
Human Readable
— ConditionsGeneral text describing weather conditions
— Weather TypeText describing significant weather conditions if any
IconWeather icon to display for the reported conditions
Relative HumidityAmount of water vapor in air relative to total possible
Sea Level PressureAtmospheric pressure adjusted for height above sea
Solar EnergyAmount of energy in the solar radiation hitting location
Contributing StationsWeather stations queried for this weather record

Temperature measures

Temperature data is composed of three values, and they are Minimum Temperature, Maximum Temperature, and average (mean) Temperature. The first two represent the minimum and maximum temperatures respectively reported during the period of this weather record. For example, if the weather record is a daily weather record, the minimum temperature value is the minimum temperature reported for that day. The maximum value is the maximum reported for that day.

The average temperature is the mean temperature calculated by combining all of the weather reports during the period of this weather record. For example, if the record is a daily weather record, then the temperature reported is the the average (mean) value for temperature across the entire day.

To learn more about temperature measures, keep reading here.

Precipitation measures

There are several important precipitation measures. These include Precipitation itself, Precipitation Coverage, Snow, Snow Depth, and Hail. Precipitation is the total amount of precipitation of any type that fell during the period. This value includes not only the amount of rain but also the amount of snow and any other non-liquid precipitation. In the case of non-liquid precipitation, the value is reported as if it were converted into water.

Precipitation coverage is a useful value that tells the length of time during the reporting period that precipitation occurred. It is always expressed as a percentage of the total time in the reporting period.

Snow and snow depth are related in that they both deal with snow. The first measure, snow, tells how much fresh snow fell from the sky during the reporting period. The snow depth measure tells how much snow is currently on the ground in areas that have not be plowed or piled.

The Visual Crossing Weather API also offers hail data. However, due to the nature of hail data, the use is somewhat different than that of the standard weather measures described above. For more information, see our article on extreme weather including hail.

To learn more about precipitation measures, keep reading here.

Wind measures

Wind data is composed of three values, and they are Wind Speed, Wind Direction, and Wind Gust. In the case of an hourly weather record, the wind speed measure reports the average wind speed over the past two-minute time window before the report. In the case of a daily weather record, wind speed reports and maximum of those hourly records throughout the day. Wind direction is closely related to wind speed. Wind direction reports the average direction of the wind during the wind speed reports. The unit shows degrees from 0 to 359 in whole numbers, where 90 equivalents to direction ‘East’, 180 to ‘South’, 270 to ‘West’ and 0 to ‘North’.

Wind gust is a weather measure that is reported only when the very short-term wind speed exceeds the reported 2-minute wind speed by more than 10 knots (11mph or 18kph). The “very short-term” period is typically defined as about 20 seconds. So, if there is a 20 second period where the wind is blowing more than 10 knots above the normally reported wind speed, this short-term wind speed is reported as a gust.

Standard wind speed is reported at 10 meters (33 feet) above the ground and recorded with an anemometer in an open area.

To learn more about wind measures, keep reading here.

Cloud and visibility measures

The two key measures, Visibility and Cloud Cover, are related in their ability to measure the visibility of the sky and the surrounding views on Earth. The visibility measure describes the horizontal opacity of the atmosphere. That is, if you are looking out at other points on the Earth, the visibility measure tells you how far away objects can be and still be identifiable.

Cloud cover tells a similar story in the vertical dimension. It tells us how much of the sky is blocked by clouds at a given time from a given location. The more clouds, the less able we are to see stars, planets and other objects in the sky including the sun for solar power.

To learn more about visibility measures, keep reading here.

“Feels like” measures

The two key “feels like” measures , Heat Index and Wind Chill, are related in their ability to measure how the body perceives a given temperature. Heat Index is a calculation that combines both temperature and humidity. The higher the combination of those two measures, the more oppressive the weather conditions feel to people and animals. However, the same temperature combined with less humidity would feel much more acceptable. Heat index is reported in degrees as a value that higher than the temperature alone.

Wind Chill is essentially the mirror of heat index for cold temperatures. However, instead of humidity being the major additional factor in the comfortable level, the culprit weather measure is wind. The wind chill calculation combines temperature and wind speed to estimate how the body “feels” in the current conditions. Wind chill is reported as a number reported in degrees that is lower than the temperature alone.

To learn more about “feels like” weather measures, keep reading here.