The challenges of measuring snow accurately

The snowfall reports that came in from eastern Nova Scotia and Prince Edward Island during the snowstorm earlier this month, while accurate, are incredible.

There was a lot of drifting, and people have been asking how accurate measurements can be taken when drifting was such an issue. It's tough but possible.

Atlantic Canada has manned weather stations at most airports and some Canadian Forces bases. Most, but not all, take measurements at several points to avoid drifting and calculate the average of these observations.

This data is included in a Meteorological Terminal Aviation Routine Weather Report (METAR) and Environment Canada's database. It's valuable but doesn't often represent city centres in our region, and the quality of the data is often called into question.

Most other Environment Canada weather stations have automatic snow measurements using acoustic snow sensors to register snow on the ground.

There are quality control issues here, too, as high winds will lead to drifting that causes the sensor to determine amounts much higher or lower than what's fallen.

“Canadian In Situ Snow Cover Trends for 1955–2017 Including an Assessment of the Impact of Automation” was a study published in 2021 and found the number of sites measuring daily snow depth has fallen 50 per cent since 1995 (Brown et al., 2021), with a large drop in ruler measurements in favour of automated sensors.

Environment Canada stations can also be few and far between, especially in rural areas, but dedicated volunteers are working to fill in the gaps.

The Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) is a network of volunteer weather observers that report precipitation, including snow, into an online database. These volunteers use a ruler and a snowboard for their measurements but will take a variety of measurements to get an average when drifting is a problem.

These dedicated volunteers are doing great work and make up most snowfall reports. However, there are still significant gaps in the official and volunteer networks.

Those interested in weather should look further into CoCoRaHS volunteering to help fill these gaps.