NWC REU 2015
May 26 - July 31



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Assessing the Skill of Updated Precipitation Type Diagnostics for Rapid Refresh With mPing

Tomer Burg, Kim Elmore, and Heather Grams


What is already known:

  • Previous studies using mPING observations showed that the Rapid Refresh (RAP) significantly under-forecasted ice pellets with near zero skill.
  • A modified ice pellet diagnostic algorithm was implemented in the RAP.
  • Parallel runs of the RAP with and without the upgrade provide an opportunity to evaluate whether precipitation type forecasts have improved.

What this study adds:

  • Statistical analysis shows that bias slightly improved for ice pellets, snow and freezing rain; skill scores improved for ice pellets and snow; and bias degraded for rain.
  • The upgrade to the RAP generates more realistic spatial distributions of precipitation type transition zones.
  • While these differences are statistically significant, they may not be practically significant.


Previous work shows that the Rapid Refresh (RAP) model severely under-represents ice pellets in its grid, with a skill near zero and a very low bias. An ice pellet diagnostic upgrade was devised at the Earth System Research Laboratory (ESRL) to resolve this issue. Parallel runs of the experimental ESRL- RAP with the fix and the operational NCEP-RAP without the fix provide an opportunity to assess whether this upgrade has improved the performance of the ESRL-RAP, both for the models overall and for individual precipitation types, using the meteorological Phenomena Identification Near the Ground (mPING) project as verification. The overall Gerrity Skill Score (GSS) for the ESRL-RAP is improved relative to the NCEP-RAP at 3 hour lead time but degrades with increasing lead time, a difference which is statistically significant but may not have much practical significance. Some improvement was found in the bias and skill scores of ice pellets and snow in the ESRL-RAP, although the model continues to under-represent ice pellets, while rain and freezing rain were generally the same or slightly worse with the fix. The ESRL-RAP was also found to depict a more realistic spatial distribution of precipitation types in transition zones involving ice pellets and freezing rain.

Full Paper [PDF]