About a month ago, the GFS was upgraded. Among other things (like making parallel GFS data available), the upgrade notice said:

  • Include hourly forecasts out to 120 hr

Now, this seemed strange to me. The NAM (which goes out to only 84 hours) outputs forecasts every 3 hours. Indeed, with the exception of very short-range models like the RAP, HRRR, and SREF (WRF), no models output data hourly. Since the NAM is intended fine-tuning shorter-range forecasts, and the GFS for longer-range patterns, why did the NWS upgrade the GFS to hourly output out to hour 120?

  • 2
    $\begingroup$ I don't know the answer, but my guess is that the demand for hourly GFS output from the public (researchers, weather and insurance companies etc.) was sufficiently large, and making these data available on NCEP's ftp servers became feasible. Given that GFS output is used both in research analysis and to initialize limited area models, it is NCEP's interest to provide as frequent output as possible. Hourly vs 3-hourly output also increases the possibilities in terms of lateral boundary conditions in limited area models. $\endgroup$ – milancurcic Jun 1 '16 at 14:21
  • $\begingroup$ Just a guess here, but if you wanted to forecast the evolution of a feature that may dissipate within three hours, it would be profitable to see it in higher temporal resolution. As a user of WRF, this makes me happy- I won't need to interpolate boundary conditions from the GFS to run it. This also means more accurate boundary conditions too. $\endgroup$ – BarocliniCplusplus Jun 1 '16 at 15:15

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