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         MISSION / VISION    |    About EMC


The North American Mesoscale Forecast System (NAM) is one of the primary vehicles by which NCEP's Environmental Modeling Center provides mesoscale guidance to public and private sector meteorologists. It is run four times daily at 00z, 06z, 12z, and 18z and consists of the following components:

- The NOAA Environmental Modeling System (NEMS) version of the Non-Hydrostatic Multi-scale Model in B-grid (NMMB) The NAM run makes forecasts for the following domains in one execution of the production run:

  1. Full North American 12 km parent domain to 84-h
  2. Four fixed nested domains run to 60-h, which are all one-way nested inside the parent 12 km domain:
    1. 4 km CONUS nest
    2. 6 km Alaska nest
    3. 3 km Hawaii and Puerto Rico nests

  3. One very high-resolution nest run to 36-h (1.33 km if over CONUS, 1.5 km if over Alaska) that is placed at different locations each cycle. During the summer fire weather season the location of this nest is usually determined by the National Interagency Fire Center and is used primarily to provide high-resolution guidance to IMETS. During the rest of the year the location is set based on requests from the NCEP Service Centers and NWS Offices.

- The NCEP regional Grid-Point Statistical Interpolation (GSI) analysis

The NAM is initialized with a 12-h run of the NAM Data Assimilation System, which runs a sequence of four GSI analyses and 3-h NEMS-NMMB forecasts using all available observations to provide a first guess to the NAM "on-time" analysis.

The NCEP High-Resolution Window Forecast System (HIRESW) consists of daily runs of the NEMS Non-hydrostatic Multiscale Model on B-grid (NEMS-NMMB) and the NCAR Advanced Research WRF (ARW) at ~3-4 km resolution. Initial conditions are provided by the NCEP Global Forecast System (GFS) for the Alaska, Hawaii, Puerto Rico, and Guam domains. The Rapid Refresh (RAP) analysis initializes the CONUS domain.

Currently, five nested domains are being run, two large domains (CONUS, Alaska) and three small domains (Hawaii, Puerto Rico, Guam). This is the current schedule:

0000Z : CONUS, Hawaii, Guam

0600Z : Alaska, Puerto Rico

1200Z : CONUS, Hawaii, Guam

1800Z : Alaska, Puerto Rico

IMPORTANT NOTE : As of 9/19/2013, preemption of the HIRESW run by the NCEP hurricane model runs has been suspended until further notice.

Additional NAM/HIRESW Information


Please mail comments, questions, suggestions about the Mesoscale Modeling Branch to Geoff DiMego, Branch Chief, at