Global Forecast System (GFS) Model

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Global Forecast System (GFS) Model

• Previous called the Aviation (AVN) and Medium
  Range Forecast (MRF) models.
• Spectral global model and 64 levels
• Relatively primitive microphysics.
• Sophisticated surface physics and radiation
• Run four times a day to 384 hr (16 days!).
• Major increase in skill during past decade
  derived from using direct satellite radiance in
  the 3DVAR analysis scheme.
• T574 (27 km) over the first 192 hours (8 days)
  of the model forecast and T190 (70 km) for 180
  through 384 hours--major implications for
  resolution change!

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GFS

• Vertical coordinates are hybrid sigma/pressure
  sigma at low levels to pressure aloft.

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Vertical coordinate comparison across North
America
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GFS Data Assimilation

• Has a later data cut-off time than the mesoscale
  modelsand thus can get a higher percentage of
  data.
• Uses much more satellite assets..thus improve
  global analysis and forecasts.
• Major gains in southern hemisphere
• Data assimilation based on 3DVAR (they call it
  GSI)

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Skill Improvements (ECMWF)

• Useful skill until
• - day 5
• 2000 - day 7
• 2003 - day 8

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GFS