This data set contains snow change measurements from interval boards collected as part of the NASA SnowEx21 time series field campaign. Surveys were conducted at field sites across the Western United States 18 November 2020 and 12 May 2021. Snow change measurements from interval boards record the height of new snow (HN) and snow water equivalent (SWE) over weekly, and in some cases biweekly, intervals. Measurements were taken using a 30 cm Snowmetrics Snow Tube and spring scale. The interval board network was expanded from the <a href="https://nsidc.org/data/snex20_ts_ib/versions/1">2020 Time Series campaign</a> to capture a broader spatial domain than previously done. A network of 4-6 interval boards accompanied a single snow pit study area varying in elevation and other physiographic characteristics. During each visit, if new snow had accumulated on the board, three samples were collected before the board was cleared and placed at the top of the snow surface. Height of new snow was measured to the nearest 0.5 cm and SWE to the nearest mm. Observers also recorded a qualitative Yes/No regarding evidence of melt on the board. These data were collected to provide ground validation for the <a href="https://nsidc.org/data/snex_uavsar/versions/1"> airborne UAVSAR L-band flights</a>. Although the variable is referred to as "height of new snow", it represents the change in snow height and SWE depth over a given interval and is therefore subject to snow settlement and/or melt between visits.