How snow is measured
There are three main variables that are collected by weather stations and trained individuals when collecting snow data:
- Snowfall: The amount of new snowfall that has fallen.
- Snow Depth: The depth of the snow on the ground – this will vary with new snow fall, existing snow fall and melting.
- Water Equivalent of Snow: The amount of water that would have fallen if the snowfall was melted. This allows for comparison with rainfall.
Snow observations are quite difficult to measure and meteorological organizations provide detailed guidance on how to measure snow. For example, the snow depth can be significantly influenced by the presence of blowing snow so that the true new snowfall is impacted by existing snowfall moving around and either reducing or increasing the apparent snow depth.
Because of the difficulty in accurately measuring snow data, unlike many other weather variables where the observation can be automated with a high degree of accuracy, snow data often relies on a trained network of observers. For this reason, snow data observations are often made on daily basis (or six hourly interval).
In the Visual Crossing Weather Data, we will interpolate daily measurements to provide data at the hourly level. For example if the snow depth is measured as 10 inches at midday on day one and 15 inches at midday on day two, we will provide hourly values that linearly increase the values from 10 to 15 inches for that 24 hour period.
In the United States, the National Weather Service train individuals via the ‘COOP National Program (COOP)‘. This has a network of over 8700 volunteers who are trained to take weather observations including snowfall data.
Snow measurement units
Snowfall is measured in centimeters (cm) in the metric units and in inches in US units. The accuracy of measurements is made to 0.1 inch in the United States.
Snow data in the weather forecast
The VIsual Crossing Weather Data products and API provide hourly snow depth and snowfall predictions as part of the weather forecast.
Snow data in the weather history requests
We recently expanded our historical snowfall data to include data from 1000s of additional officially trained snowfall observers. When a weather station does not report automated snow data, we will include the closest snowfall data from nearby trained snow data.