Snow Accumulation Forecasting Using NWP
Introduction
Forecasting snow accumulation is a difficult task, and not just because initial observational uncertainties and subtle atmospheric processes can lead to major precipitation type and intensity forecast errors. The various NWP models and ensembles use different numerical methods and post-processing techniques, resulting in important differences in how snow accumulation products are derived. In addition, snowfall forecast graphics on AWIPS and found on various websites and social media platforms use different assumptions, which can create a lot of confusion and uncertainty. The purpose of this guide is to help forecasters learn the assumptions and limitations associated with the creation of snowfall accumulation forecast products derived from NWP models and ensembles.
In the following pages, you will learn more about the physical process associated with snow accumulation (part 1), uncertainties associated with how snow is measured (part 2), how numerical models determine precipitation type (part 3), how models internally calculate snowfall accumulation (part 4), and how AWIPS and websites create snowfall accumulation graphics (part 5). Finally, there is a reference document for how different models parameterize, calculate, and produce output for snowfall (part 6). This guide is intended to be a living document, and changes will be incorporated as they are documented.
This guide is not intended to cover the broader topic of forecasting winter weather, but instead focuses on snow accumulation products derived from NWP models and ensembles. For more a more comprehensive overview of forecasting hazardous winter weather, visit the Warning Decision Training Division’s Winter Warning Operations Course.