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The High Resolution Ensemble Forecast (HREF) produces ensemble products from several different models running at ~3 km horizontal grid spacing. Three of the models utilized in HREF come from the High Resolution Window: two different configurations of the Advanced Research Weather Research and Forecasting (WRF-ARW) model and a single Nonhydrostatic Multiscale Model on B-grid (NMMB) run. For the CONUS HREF, the North American Model (NAM) 3 km CONUS nest also is utilized. Information from these models is used in a time-lagged fashion, with the two most recent runs of each system combined into an 8-member ensemble (CONUS) and a 6-member ensemble for HI, AK, and PR (two fewer members as NAM nest output is not used for these domains). This system produces ensemble products for four different domains on the following schedule, with output at hourly temporal resolution to 36 h:

00Z (CONUS and Hawaii)
06Z (CONUS, Alaska, and Puerto Rico)
12Z (CONUS and Hawaii)
18Z (CONUS, Alaska, and Puerto Rico)

Five different types of output are produced:
*mean: Arithmetic mean of all members.
*pmmn: A “probability matched” mean, which combines information from the ensemble
mean with the amplitude of the individual members.
*avrg: An averaging of the mean and pmmn output.
*sprd: The spread of the ensemble, which is a measure of how different the individual
model runs are for a variable at a given point (smaller spread indicates better
agreement within the ensemble)
*prob: Probabilistic output; the percentage of the membership meeting a specified threshold
such as > 0.5” of accumulated precipitation in a 6 h period).


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