Knowledge Base

How do I import SNODAS data into ArcGIS?

Follow the steps below, which are also linked to from the SNODAS user guide. These steps will work for all 8 SNODAS variables using ArcGIS 10.0 or higher.

Before working through the rest of this tutorial, we would like to make you aware of a small spatial data shift that occurs on Oct 01, 2013 in the SNODAS period of record. On this date, the data provider, National Operational Hydrologic Remote Sensing Center (NOHRSC) slightly changed the center coordinates of the grid to align with an integer value of latitude and longitude. The resulting shift is minute, and on the order of 1/4 of a 1km grid cell. If you decide your study is insensitive to this change, please use the static geospatial bounds presented within the examples. If you wish to account for the shift in your study, you can find the spatial bounds for the data both before and after the Oct 01, 2013 change in Appendix 2 of this How To document. In addition, you may wish to reference the .Hdr files that are provided with the .gz data files for the precise geolocation information for each file.


1. Create one of the following header files based on your dates and give it the same name as "filename" but with a .hdr extentsion. Remember to place in the same directory as "filename.dat".

For masked data processed before Oct 01 2013 (files beginning with 'us'):

nrows 3351
ncols 6935
nbands 1
nbits 16
pixeltype signedint
byteorder M
layout dat
ulxmap -124.729583333331703
ulymap 52.871249516804028
xdim 0.00833333333
ydim 0.00833333333

For masked data processed after Oct 01 2013 (files beginning with 'us'):

nrows 3351
ncols 6935
nbands 1
nbits 16
pixeltype signedint
byteorder M
layout dat
ulxmap -124.733333333333
ulymap 52.8749999999999
xdim 0.00833333333
ydim 0.00833333333 

For unmasked data processed before Oct 01 2013 (files beginning with 'zz'):

nrows 4096
ncols 8192
nbands 1
nbits 16
pixeltype signedint
byteorder M
layout dat
ulxmap -130.517083333328
ulymap 58.2329166666644
xdim 0.00833333333
ydim 0.00833333333 

For unmasked data processed after Oct 01 2013 (files beginning with 'zz'):

nrows 4096
ncols 8192
nbands 1
nbits 16
pixeltype signedint
byteorder M
layout dat
ulxmap -130.516666666661
ulymap 58.2333333333310
xdim 0.00833333333
ydim 0.00833333333

2. Start ArcMap and click on the 'Add Data' icon located in the main toolbar. Browse, select, and open the .dat file to the map document. To add the file in a different format, follow step 3.

3. Start ArcMap and open ArcToolbox. Select Conversion Tools > To Raster > Raster to Other Format. The Raster to Other Format window will appear. In the Input Raster box, browse and select the .dat file. In the Output Workspace box, select the location to store the new data set. In the Output Format box, select the format you wish to create (e.g. TIFF, ENVI DAT, etc.). Click OK.

Appendix 2.  Masked spatial bounds for pre and post Oct 01 2013.

Pre Oct 01 2013: -124.73375000 52.87458333 -66.94208333 24.87458333

Post Oct 01 2013: -124.73333333 52.87500000 -66.94166667 24.95000000

Last Updated 30 November 2018

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