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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 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 WRF versions of the non-hydrostatic, hybrid vertical coordinate mesoscale model (NMM) and the NCAR Advanced Research WRF (ARW) at ~5 km resolution. All runs except the Alaska domain use the NAM for initial and boundary conditions. The Alaska run uses the NCEP Global Forecast System (GFS) for initial/boundary conditions. Currently, six nested domains are being run, three large domains (East/Central U.S., West/Central U.S., Alaska) and three small domains (Hawaii, Puerto Rico, Guam). This is the current schedule:

0000Z : East/Central U.S., Hawaii, Guam

0600Z : West/Central U.S., Puerto Rico

1200Z : East/Central U.S., 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 for the remainder of the 2013 hurricane season. Preemption will be reinitiated after the 2014Q2 HIRESW upgrade is implemented.

Additional NAM/HIRESW Information


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