The SnowEx Science Plan describes the science traceability matrix (STM), which was developed for SnowEx mission objectives and ancillary questions, mission requirements, and data deliverables that will help address the overarching and fundamental questions. The STM was developed after the 2016-2017 SnowEx campaign and was based on science questions and requirements articulated by the wider community at prior workshops (e.g., SnowEx, iSWGR) and in the recent Decadal Survey, as well as motivating questions and outcomes of the first SnowEx campaign. A catalog of community-identified questions was compiled and rated by the NASA THP-16 investigators in regards to perceived importance to SnowEx. This was the basis for the overarching and fundamental questions in the STM. The set of four Mission Objectives/Ancillary Questions (column 1 in STM) derive from the two fundamental questions, and include subcomponents to address gaps in our knowledge of state variables, fluxes, physical processes, and measurement techniques. The measurement requirements, instrument functional requirements, investigation functional requirements, and data deliverables (columns 2-4 in STM) were originally articulated in the SnowEx 2016-2017 STM and maintain relevance to the multi-year campaign. The intent of the developed STM is to provide fundamental science questions and associated mission objectives and ancillary questions that are specific and granular enough to support campaign- scale planning, yet also have sufficient scope and diversity to enable multiple years of SnowEx scoping and implementation, depending on resource availability, PI participation, and instrument development and application, among other factors.