Seasonal evolution of a warm alpine snowpack: a multi-instrument dataset of snow microstructure at Col de Porte, French Alps

Abstract. Long-term snow observation sites provide valuable datasets for understanding snowpack evolution and evaluating snow models. Recent observation campaigns have progressively enriched these monitoring programs with high-resolution measurements of snow microstructure, particularly using the SnowMicroPen. Here, we present a two-winter dataset of snow and atmospheric observations collected at Col de Porte (French Alps, 1325 m), a warm alpine environment, during the winters 2021–2022 and
2022–2023. The dataset extends the standard observation program with weekly vertical profiles of snow density, specific surface area (SSA), structural anisotropy, and penetration resistance obtained from the SnowMicroPen, X-ray tomography, density cutters, and two optical reflectance instruments (DUFISSS and HISSGraS). Tomography measurements combined fast acquisitions (42 μm) and high-resolution acquisitions (10 μm). The study (i) provides a comprehensive dataset of snow microstructural properties together with atmospheric forcing for snow model evaluation under warm snow conditions, characterized by frequent wet snow and melt-freeze crusts, and (ii) assesses the strengths and limitations of the different measurement techniques, including the feasibility of seasonal snowpack monitoring by X-ray tomography, the use of the SnowMicroPen under warm snow conditions, and the agreement between the two optical reflectance instruments. The paper describes the meteorological and snowpack conditions during the two winters, presents multi-instrument vertical profiles of snow density and SSA, and reports the characteristic ranges of density, SSA, and structural anisotropy for the different snow types encountered at Col de
Porte. The dataset is available at https://doi.org/10.6084/m9.figshare.33426472 (Calonne et al., 2026).