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Abstract. Modeling the multidimensional flow of liquid waterthrough snow has been limited in spatial and temporal scales to date. Here,we present simulations using the inverse TOUGH2 (iTOUGH2) model informed by the modelSNOWPACK, referred to as SnowTOUGH. We use SnowTOUGH to simulate snowmetamorphism, melt/freeze processes, and liquid water movement intwo-dimensional snowpacks at the plot scale (20 m) on a sloping groundsurface during multi-day observation periods at three field sites innorthern Colorado, USA. Model results compare well with sites below the treelineand above the treeline but not at a site near the treeline. Results show theimportance of longitudinal intra-snowpack flow paths (i.e., parallel toground surface in the downslope direction and sometimes referred to aslateral flow), particularly during times when the snow surface (i.e.,snow–atmosphere interface) is not actively melting. At our above-treelinesite, simulations show that longitudinal flow can occur at rates orders ofmagnitude greater than vertically downward percolating water flow at a meanratio of 75:1 as a result of hydraulic barriers that divert flow. Our near-treeline site simulations resulted in slightly less longitudinal flow thanvertically percolating water, and the below-treeline site resulted innegligible longitudinal flow of liquid water. These results show theincreasing influence of longitudinal intra-snowpack flow paths withelevation, similar to field observations. Results of this study suggest thatintra-snowpack longitudinal flow may be an important process forconsideration in hydrologic modeling for higher-elevation headwatercatchments.