Context-For a better understanding of how much water is contained in each winter’s snowfall and how much will be available when it melts in the spring, NASA has launched a seasonal campaign — part of a five-year programme called SnowEx, initiated in 2016-17.

• While the geographical focus of SnowEx is North America, NASA’s overall target is optimal strategies for mapping global snow water equivalent (SWE) with remote sensing and models leading to a Decadal Survey “Earth System Explorer” mission.
• SnowEx assesses where snow has fallen, how much there is and how its characteristics change as it melts. It uses airborne measurements, ground measurements and computer modelling.