The The Snowmelt Parametric Aggregation Calculator (SnowPAC) is a numerical tool for estimating ATI-Meltrate functions for use in Temperature Index snowmelt modeling in HEC-HMS. The tool requires daily historical time series data of temperature, snow water equivalent (SWE), and precipitation.

SnowPAC is launched from the Tools | Snowmelt | SnowPAC menu in HEC-HMS.

A project must be open to access the SnowPAC tool.

For more information, see the Technical Reference Manual.

For a step-by-step guide on using SnowPAC with example data, see the Tutorials & Guides.

SnowPAC aids in rapid estimation of ATI-Meltrate functions for use in the Temperature Index snowmelt method in HMS. SnowPAC uses three inputs of daily time series data: temperature, precipitation, and snow water equivalent (SWE). ATI-Meltrate functions can be estimated for multiple "melt events" across multiple water years for a single combination of gage inputs. ATI-Meltrate functions can be exported to DSS and to the HMS project.

SnowPAC is a wizard tool that contains 6 steps.

  1. Select unit system and time-series data
  2. Set analysis window
  3. Define melt events
  4. Refine ATI-meltrate functions
  5. Review and compare ATI-meltrate functions
  6. Export to project and DSS

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