Probabilistic Forecasting of Winter Weather: HREF Applications

Probabilistic Forecasting of Winter Weather: HREF Applications

High-Resolution Ensemble Forecast (HREF) systems are the next generation of ensemble prediction systems. HREFs provide high-resolution probabilistic forecast information, including the location of mesoscale precipitation bands, and the probability of exceeding important temperature, precipitation, and wind thresholds at the scale of the HREF.

For Impact-based Decision Support Services (IDSS), many emergency managers and other NWS core partners base decisions on specific thresholds for snow accumulation, temperature, and other weather elements. Probabilistic forecasts can help inform the likelihood that these thresholds are met.

This lesson addresses the application of the NWS HREF to an early winter storm in the New York City region. This lesson includes the following sections:

  • A description of the HREF produced at the Environmental Modeling Center (EMC),
  • The types of products currently provided for winter weather guidance, and
  • The case example where the probabilistic winter weather guidance is used.

We will also provide additional information on statistical methods used to produce the weather elements available from the HREF, including:

  • Percentiles / probability of exceedance
  • Conditional vs unconditional probability of precipitation Type
  • Point Probability / Neighborhood probability / Ensemble Agreement Scale (EAS) probability