Operational Forecasting Models

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Operational Forecasting Models
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NWS Operational Models

• Global Forecasting System (GFS)
• North American Mesoscale (NAM)
• Eta (ETA)
• Nested Grid Model (NGM)
• Rapid Update Cycle (RUC)

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Global Forecasting System (GFS)

• The GFS model was previously called the Aviation
  (AVN) model and the Medium Range Forecast (MRF)
  model.
• The GFS model was developed by the NWS as part of
  the Global Data Assimilation and Forecast System
  (GDAS).

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GFS (Cont.)

• The GFS model was originally developed to improve
  forecasts of global, longwave weather systems.

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GFS (Cont.)

• The GFS model
• is a global model,
• is a spectral model,

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GFS (Cont.)

• The GFS model
• has 64 vertical levels,
• uses sigma as the vertical coordinate.
• is a hydrostatic model,

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GFS (Cont.)

• The GFS model
• has a horizontal grid resolution of approximately
  80 km,
• is run to produce forecasts out to 384 hours.

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The North American Mesoscale (NAM) Model

• The North American Mesoscale (NAM) model is
  designed to provide forecasters with high
  resolution guidance over the U.S. for short range
  forecasts.
• The Weather Research and Forecasting (WRF) model
  replaced the Eta model as the NAM model on June
  20, 2006.

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NAM (Cont.)

• The NAM model
• is a regional model,
• is a grid-point model,

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NAM (Cont.)

• The NAM model
• has 60 levels,
• uses sigma as the vertical coordinate,
• is a non-hydrostatic model.

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The NAM (Cont.)

• The NAM model
• has a horizontal grid resolution of 12 km,
• is run to produce forecasts out to 84 hours.

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The Eta (ETA) Model

• The ETA model was designed to provide forecasters
  with better guidance about convective
  precipitation, mesoscale flash floods and severe
  weather events.

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ETA (Cont.)

• The Eta coordinate was developed to try to reduce
  errors in the computation of the horizontal
  pressure gradient force that can occur with the
  sigma vertical coordinate.
• The Eta coordinate is sometimes called the step
  mountain coordinate.

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ETA (Cont.)

• The ETA model
• is a regional model,
• is a grid-point model.

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ETA (Cont.)

• The ETA model
• has 60 levels,
• uses Eta as the vertical coordinate,
• is a hydrostatic model.

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ETA (Cont.)

• The ETA model
• has a horizontal grid resolution of 12 km,
• is run to produce forecasts out to 84 hours.

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Nested Grid Model (NGM)

• The Nested Grid Model (NGM) was introduced by the
  National Weather Service in 1985 as part of the
  Regional Analysis and Forecast System (RFAS).

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NGM (Cont.)

• The purpose of the NGM was to provide improved
  numerical guidance through 48 hours, with
  principal emphasis on improved prediction of
  quantitative precipitation and significant
  weather events.

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NGM (Cont.)

• The NGM has not been changed since 1990.

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NGM (Cont.)

• The NGM
• is a regional model,
• is a grid-point model.

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NGM (Cont.)

• The NGM
• has 18 levels,
• uses sigma as the vertical coordinate
• is a hydrostatic model.

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NGM (Cont.)

• The NGM
• has a horizontal grid resolution of 80 km,
• is run to produce forecasts out to 48 hours.

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Rapid Update Cycle (RUC) Model

• The Rapid Update Cycle (RUC) model was designed
  to provide accurate forecast guidance for weather
  sensitive users for the next 12 hour period.
• The RUC model was originally implemented in 1994
  and the current version is called RUC-13.

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RUC Model (Cont.)

• The RUC model
• is a regional model,
• is a grid-point model.

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RUC Model (Cont.)

• The RUC model
• has 50 levels,
• uses a hybrid isentropic-sigma coordinate,
• is a hydrostatic model.

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RUC Model (Cont.)

• The RUC model
• has a horizontal grid resolution of 13 km,
• is run to produce forecasts out to 12 hours,
• is run every hour, as new data arrive.

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Other Forecast Models

• Numerous other government agencies, universities,
  and private businesses in the U.S. and around the
  world run meteorological models to produce
  forecast guidance.

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NOGAPS

• The U.S. Navy run the Naval Operational Global
  Atmospheric Prediction System (NOGAPS) which is a
  global spectral model with 30 vertical levels and
  a horizontal grid resolution of 55 km.

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MM5

• The Penn State/NCAR Mesoscale Model version 5
  (MM5) is a grid-point model that can be
  configured to run for any location around the
  world.
• The Byrd Polar Research Center (BPRC) at Ohio
  State runs a version of MM5 centered on Ohio with
  a horizontal grid resolution of 30 km.

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AFWA

• The Air Force Weather Agency (AFWA) runs a
  non-hydrostatic version of MM5 with 42 vertical
  levels and three nested grids with horizontal
  resolutions of 45 km, 15 km and 5 km.

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GEM

• The Canadian Meteorogical Centre runs a Global
  Environmental Multiscale (GEM) model that has 58
  vertical levels and approximately a 50 km
  horizontal grid resolution.

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UKMET and ECMWF

• Both the United Kingdom Meteorological Office
  (UKMET) and the European Center for Medium Range
  Weather Forecasting (ECMWF) run global models for
  weather forecasting.

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Ensemble Forecasts

• Ensemble forecasts refer to the process of
  combining forecasts from multiple sources.
• For example, an ensemble model forecast might
  combine the results of different models, or
  combine the result of runs of the same model
  initialized with slightly different conditions.

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NWS Global Ensemble

• The NWS runs a simplified version of the GFS in
  order to create its global ensemble guidance.
• The GFS ensemble consists of 20 members plus a
  control run.

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NWS Global Ensemble (Cont.)

• The simplified version of the GFS model used for
  the ensemble runs
• has 28 levels, and
• has a horizontal grid resolution of approximately
  300 km.