NDFD data are stored as points on regular grids. There are 6 grids with each grid derived from points projected from a sphere of radius 6371.2 km. The CONUS and Northern Hemisphere grids use a Lambert Conformal projection while the Guam, Hawaii, Puerto Rico, and Northern Pacific grids use a Mercator projection. The Alaska grid is based on a Polar Stereographic projection. Additional meta-data on NDFD grids are available in three grid definition tables below.

The NDFD uses the World Geodetic System 1984 (WGS84) ellipsoid for its horizontal datum.

Any latitude and longitude value provided as input to an NWS NDFD service (i.e. Simple Object Access Protocol Web Service, degrib custom sectors, etc.) or returned in output from one of these services has a horizontal datum defined by the WGS84.

**NOTE**: For users planning to reconstruct grids using GRIB2 files, please see the grid meta-data section below.

The NDFD uses elevation values referenced to mean sea level as represented by the WGS84 geoid.

CONUS Grid

Northern Hemisphere Grid

Alaska Grid

Guam Grid

Hawaii Grid

Puerto Rico Grid

Northern Pacific Grid

Oceanic Grid

The NDFD grids, as described in the tables below, are the result of projecting a sphere onto a flat surface. The corner of the grid is found at the point identified in the grid parameters tables as latitude1 and longitude1. Each table lists the number of points in the grid which is the product of the number of points on the parallel and meridian. Grid points are seperated by Dx meters along the x axis (longitude) and Dy meters along the y axis (latitude). The projection type, earth radius, and other grid definition parameters are provided in the tables below. For more information on decoding GRIB2 files, see the section on GRIB2 Links.

Grid Parameter | CONUS 5km | CONUS 2.5km | Northern Hemisphere |
---|---|---|---|

Number of Points | 739297 | 2953665 | 1509825 |

Projection Type | Lambert Conformal | Lambert Conformal | Lambert Conformal |

Shape of Earth | sphere | sphere | sphere |

Earth Radius | 6371.2 km | 6371.2 km | 6371.2 km |

Number of Points on the parallel | 1073 | 2145 | 1473 |

Number of Points on the Meridian | 689 | 1377 | 1025 |

Latitude1 | 20.191999 | 20.191999 | 12.189999 |

Longitude1 | 238.445999 | 238.445999 | 226.541000 |

u/v vectors relative to | easterly/northerly | easterly/northerly | easterly/northerly |

Dx | 5079.406 m | 2539.703 m | 5079.406 m |

Dy | 5079.406 m | 2539.703 m | 5079.406 m |

GRIB2 grid, scan mode | 64 (0100) | 64 (0100) | 64 (0100) |

Scan i/x direction | positive | positive | positive |

Scan j/y direction | positive | positive | positive |

Consecutive points in | i/x direction | i/x direction | i/x direction |

Adjacent rows scan in | same direction | same direction | same direction |

Mesh Latitude | 25 | 25 | 25 |

Orientation Longitude | 265 | 265 | 265 |

Which Pole is on the Plane | north | north | north |

Is Projection Bi-polar | no | no | no |

Tangent Latitude1 | 25 | 25 | 25 |

Tangent Latitude2 | 25 | 25 | 25 |

Southern Latitude | -90 | -90 | -90 |

Southern Longitude | 0 | 0 | 0 |

Grid Parameter | Guam | Hawaii | Puerto Rico | N. Pacific | Oceanic |
---|---|---|---|---|---|

Number of Points | 37249 | 72225 | 75936 | 1580529 | 4512981 |

Projection Type | Mercator | Mercator | Mercator | Mercator | Mercator |

Shape of Earth | sphere | sphere | sphere | sphere | sphere |

Earth Radius | 6371.2 km | 6371.2 km | 6371.2 km | 6371.2 km | 6371.2 km |

Number of Points on the parallel | 193 | 321 | 339 | 1473 | 2517 |

Number of Points on the Meridian | 193 | 225 | 224 | 1073 | 1793 |

Latitude1 | 12.349884 | 18.072699 | 16.977485 | -25.000000 | -30.4192 |

Longitude1 | 143.686538 | 198.474999 | 291.972167 | 110.000000 | 129.906000 |

u/v vectors relative to | easterly/northerly | easterly/northerly | easterly/northerly | easterly/northerly | easterly/northerly |

Latitude2 | 16.794399 | 23.087799 | 19.544499 | 60.643999 | 79.991525 |

Longitude2 | 148.280000 | 206.130999 | 296.015600 | 250.871000 | 10.689223 |

Dx | 2500.0 m | 2500.0 m | 1250.0 m | 10000.0 m | 10000.0 m |

Dy | 2500.0 m | 2500.0 m | 1250.0 m | 10000.0 m | 10000.0 m |

GRIB2 grid, scan mode | 64 (0100) | 64 (0100) | 64 (0100) | 64 (0100) | 64 (0100) |

Scan i/x direction | positive | positive | positive | positive | positive |

Scan j/y direction | positive | positive | positive | positive | positive |

Consecutive points in | i/x direction | i/x direction | i/x direction | i/x direction | i/x direction |

Adjacent rows scan in | same direction | same direction | same direction | same direction | same direction |

Mesh Latitude | 20 | 20 | 20 | 20 | 20 |

Orientation Longitude | 0 | 0 | 0 | 0 | 0 |

Tangent Latitude1 | 0 | 0 | 0 | 0 | 0 |

Tangent Latitude2 | 0 | 0 | 0 | 0 | 0 |

Southern Latitude | 0 | 0 | 0 | 0 | 0 |

Southern Longitude | 0 | 0 | 0 | 0 | 0 |

Grid Parameter | Alaska 6km | Alaska 3km |
---|---|---|

Number of Points | 456225 | 1822145 |

Projection Type | Polar Stereographic | Polar Stereographic |

Shape of Earth | sphere | sphere |

Earth Radius | 6371.2 km | 6371.2 km |

Number of Points on the parallel | 825 | 1649 |

Number of Points on the Meridian | 553 | 1105 |

Latitude1 | 40.530101 | 40.530101 |

Longitude1 | 181.429000 | 181.429000 |

u/v vectors relative to | easterly/northerly | easterly/northerly |

Dx | 5953.125 m | 2976.5625 m |

Dy | 5953.125 m | 2976.5625 m |

GRIB2 grid, scan mode | 64 (0100) | 64 (0100) |

Scan i/x direction | positive | positive |

Scan j/y direction | positive | positive |

Consecutive points in | i/x direction | i/x direction |

Adjacent rows scan in | same direction | same direction |

Mesh Latitude | 60 | 60 |

Orientation Longitude | 210 | 210 |

Which Pole is on the Plane | north | north |

Is Projection Bi-polar | no | no |

Tangent Latitude1 | 90 | 90 |

Tangent Latitude2 | 90 | 90 |

Southern Latitude | 0 | 0 |

Southern Longitude | 0 | 0 |

- World Meteorological Organization FM92 GRIB, Edition 2, Code Form and Tables publication
- GRIB2 Use at NCEP