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Access Data

NDFD Grids

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.

NDFD Horizontal Datum

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 Servicedegrib 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.
 

NDFD Vertical Datum

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

Grid Locations and Extent

CONUS Grid Image of the CONUS Grid
Northern Hemisphere Grid Image of the Northern Hemisphere Grid
Alaska Grid Image of the Alaska Grid
Guam Grid Image of the Guam Grid
Hawaii Grid Image of the Hawaii Grid
Puerto Rico Grid Image of the Puerto Rico Grid
Northern Pacific Grid Image of the Northern Pacific Grid
Oceanic Grid Image of the Oceanic Grid

Details of NDFD Grids Found in GRIB2 Meta Data

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.

CONUS and Northern Hemisphere Grids

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

Guam, Hawaii, Puerto Rico Grids, Northern Pacific and Oceanic Grids

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

Alaska Grid

Grid Parameter Alaska
Number of Points 456225
Projection Type Polar Stereographic
Shape of Earth sphere
Earth Radius 6371.2 km
Number of Points on the parallel 825
Number of Points on the Meridian 553
Latitude1 40.530101
Longitude1 181.429000
u/v vectors relative to easterly/northerly
Dx 5953.125 m
Dy 5953.125 m
GRIB2 grid, scan mode 64 (0100)
Scan i/x direction positive
Scan j/y direction positive
Consecutive points in i/x direction
Adjacent rows scan in same direction
Mesh Latitude 60
Orientation Longitude 210
Which Pole is on the Plane north
Is Projection Bi-polar no
Tangent Latitude1 90
Tangent Latitude2 90
Southern Latitude 0
Southern Longitude 0

GRIB2 Links

GRIB2 Documentation

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

GRIB2 Decoders

Sources of GRIB2 Files