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This data set contains output from the NOAA National Weather Service's National Operational Hydrologic Remote Sensing Center (NOHRSC) SNOw Data Assimilation System (SNODAS). SNODAS is a modeling and data assimilation system developed by NOHRSC to provide the best possible estimates of snow cover and associated variables to support hydrologic modeling and analysis. The aim of SNODAS is to provide a physically consistent framework to integrate snow data from satellite and airborne platforms, and ground stations with model estimates of snow cover (Carroll et al. 2001). SNODAS includes procedures to ingest and downscale output from Numerical Weather Prediction (NWP) models, and to simulate snowcover using a physically based, spatially-distributed energy- and mass-balance snow model. SNODAS also includes procedures to assimilate satellite-derived, airborne, and ground-based observations of snow covered area and Snow Water Equivalent (SWE).
These data are not suitable for snow fall events or totals for specific regions. For snow fall data, please see the state climatology reports for a particular state. These are gridded data sets for the continental United States at 1 km spatial resolution and 24 hour temporal resolution. Data are stored in flat binary 16-bit signed integer big-endian format with header and metadata files, and are available from 1 October 2003 to present via FTP.
To broaden awareness of our services, NSIDC requests that you acknowledge the use of data sets distributed by NSIDC. Please refer to the citation below for the suggested form, or contact NSIDC User Services for further information. We also request that you send us one reprint of any publication that cites the use of data received from our Center. This helps us to determine the level of use of the data we distribute. Thank you.
The following example shows how to cite the use of these data sets in a publication. List the principal investigators, year of data set release, data set title and version number, dates of the data you used (for example, March to June 2004). Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.
National Operational Hydrologic Remote Sensing Center. 2004. Snow Data Assimilation System (SNODAS) Data Products at NSIDC, [list the dates of the data used]. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.
| Category | Description |
|---|---|
| Data format | Flat binary, 16-bit signed integer (big-endian) |
| Spatial coverage and resolution | Contiguous United States and parts of Canada: Southernmost Latitude: 24.9504 ° N |
| Temporal coverage and resolution | 1 October 2003 to present. 24-hour temporal resolution. See the table Daily NOHRSC SNODAS Products at NSIDC for more information. |
| Grid type and size | Grid values are 16-bit signed integers (big-endian) Grids are 6,935 columns by 3,351 rows |
| Projection Description | Projection: Geographic (latitude/longitude coordinates) Datum: WGS 1984 |
| File naming convention | FTP Daily files: SNODAS_YYYYMMDD.tar FTP Monthly files: SNODAS_YYYYMM.tar |
| File size | Compressed file sizes vary greatly depending on snow coverage; uncompressed size is 46.5 MB with a 3.6 - 3.8 KB header file. |
| Parameters | Snow Water Equivalent (SWE)
Snow Depth Snow Melt Runoff at the Base of the Snow Pack Sublimation from the Snow Pack Sublimation of Blowing Snow Solid Precipitation Liquid Precipitation Snow Pack Average Temperature |
| Procedures for obtaining data | Data are available via FTP. For subsetting options, please see the Graphical Interface for Subsetting, Mapping, and Ordering (GISMO) Web site. |
Andrew P. Barrett
National Snow and Ice Data Center
Cooperative Institute for Research in Environmental Sciences
University of Colorado
449 UCB
Boulder, CO 80309
USA
Thomas Carroll (Retired)
National Weather Service
National Operational Hydrologic Remote Sensing Center
1735 Lake Drive W.
Chanhassen, MN 55317
USA
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org
NOHRSC, located in Minneapolis, Minnesota, provides snow information in a variety of products and formats to meet operational forecasting needs. Most of these products are available from the NOHRSC Web site. NSIDC and NOHRSC have agreed that NSIDC will archive and distribute selected parameters from the NOHRSC SNODAS. These output files are valuable for hydrologists, hydrologic modelers, climatologists, ecologists, and land surface modelers. This documentation draws heavily on an assessment of SNODAS products by Barrett (2003) and on material provided by NOHRSC. Consult these sources for additional information.
The SNODAS product is model output and should not be confused with actual observations. For information on snow fall events or snow fall totals, please contact one of the climate centers listed below:
Eight driving, state, and diagnostic variables are archived by NSIDC. Driving variables are ingested from the Rapid Update Cycle 2 (RUC2) NWP model and used to force the snow model. State variables are defined here as variables that the snow model keeps track of and that describe the state of the model snow pack. State variables are modeled snow pack characteristics that are also required to initialize the model. Diagnostic variables are model output but do not describe the internal state of the model. The variables archived by NSIDC are listed in Table 1 and can be used to compute snow water balance.
SNODAS data files are supplied to NSIDC as flat binary 16-bit signed integer big-endian grids. A header file is also supplied to NSIDC as a text file, which includes metadata. The data files can be read by user-written routines such as Fortran and C programs, off-the-shelf image processing packages such as ENVI, IDL, MATLAB, and ERDAS IMAGINE, and by GIS and other mapping packages such as GMT, GRASS, and ARC/INFO. For instructions, such as importing files into ENVI, refer to Barrett (2003).
The header files contain information to georegister grids contained in the flat binary files. They also contain information about creation and modification of each file, data type of each file, georeferencing data, maximum and minimum values, calibration/scaling information, and a time stamp for each field. Two attributes of the header file that most users will want to pay attention to are the minimum/maximum x and y axis coordinates. These are the grid cell edges that define the extents of the grid.
If you are using ArcMap to display and analyze SNODAS products, the data will not display correctly and values may be modified. This modification occurs because SNODAS data are signed integers and ArcMap reads unsigned integers. You will need to perform the Map Algebra function in ArcMap in order to correct the data. For instructions on how to perform the Map Algebra function in ArcMap, go to the Importing SNODAS Data into ArcGIS document.
If you are using SNODAS products in ArcMap, the data will display improperly and the values will be off because these data are signed integers and ArcMap can only read unsigned integers. You will need to perform the Map Algebra function in ArcMap in order to byte swap the data. For instructions on how to perform the Map Algebra function in ArcMap, go to the Importing SNODAS Data into ArcGIS document.
The data and header files that are received from NOHRSC have an extension .grz. However, NSIDC tars and zips these files and renames them with the extension .tar.gz. Renaming is done in order to make the files easier to uncompress. The tarred and zipped files are then bundled into daily tar files and placed on the FTP site. Every two months, all of the daily tar files are compressed into a monthly tar file. However, the daily tar files remain in the same directory with the monthly tar file for approximately two months before they are deleted.
There are two ways to obtain data, either through the regular FTP access link or through the Graphical Interface for Subsetting, Mapping, and Ordering (GISMO). See the Data Access section of this document for more information on obtaining the data. The file naming convention is different depending on how the files were obtained. When obtaining data through the regular FTP access link, you will receive a regular file such as us_ssmv11034tS__T0001TTNATS2003102305HP001.dat, and when obtaining data through GISMO, you will receive a subsetted file such as subset_us_ssmv11036tS__T0001TTNATS2005122605HP001.dat.bil.Z.
Follow the links below to see the file naming convention for that type of file:
The data are available through the FTP site as daily tar files with the following naming convention and as described in Table 2:
SNODAS_YYYYMMDD.tar
Where:
| Variable | Description |
|---|---|
| SNODAS | Identifies this as SNODAS data |
| YYYY | 4-digit year |
| MM | 2-digit month |
| DD | 2-digit day of month |
| .tar | Identifies that this file has been tarred |
 |
| Figure 1. Example of FTP Site Daily Tar Files |
Every two months, all of the daily tar files are compressed into a monthly tar file with the following naming convention and as described in Table 3:
SNODAS_YYYYMM.tar
Where:
| Variable | Description |
|---|---|
| SNODAS | Identifies this as SNODAS data |
| YYYY | 4-digit year |
| MM | 2-digit month |
| .tar | Identifies that this file has been tarred |
 |
| Figure 2. Example of FTP Site Monthly Tar Files |
Note: The daily tar files remain in the same directory with the monthly tar file for approximately two months before the daily tar files are deleted. The unzipped monthly tar files contain all of the daily tar files for the month and year stated in the file name of the monthly tar files. See the Daily Tar Files section of this document for a description of their naming convention.
Each FTP daily tar file contains tarred and zipped data and header files with a .tar.gz extension. The .tar.gz filenames have the following format and are described in Table 4:
rr_mmmffppppSvvvvTttttooooTSyyyymmddhhIPOOO.xxx
Where:
 |
| Figure 3. Example of FTP Site Data and Header Tarred and Zipped Files |
Each .tar.gz file contains a data and a header file. The data and header files share the same filename with the exception of the file extension. Data files have the extension .dat and header files have the extension .Hdr. The.dat and .Hdr filenames have the following format:
rr_mmmffppppSvvvvTttttooooTSyyyymmddhhIPOOO.xxx
See Table 4 for a description of the variables in the file name.
 |
| Figure 4. Example of FTP Site Data and Header Files |
The tarred data files that are returned from the GISMO interface are named according to the time that they were ordered based on USA Mountain Time. If you ordered a large quantity of data, you may receive multiple tar files that are all numbered. The number begins with zero, and only the zero numbered file contains the header file. The GISMO files have the following naming convention and are described in Table 5:
YYYYMMDDHHmm-f.tar
Where:
Because GISMO subsets the data, the names of the data files are slightly different from the way they are named on the FTP site. Specifically, it adds the word subset to the beginning of the file. The naming convention is as follows:
subset_rr_mmmffppppSvvvvTttttooooTSyyyymmddhhIPOOO.dat.<user_selected_output>
The variable <user_selected_output> is dependent on the output you selected from GISMO. For a description of the other file naming variables, see Table 4.
When you order data via GISMO, you will see a .hdr file in the first tar file of the GISMO request; this tar file ends in -0.tar. The header file is named similarly to the GISMO tar file:
YYYYMMDDHHmm.hdr
Where .hdr indicates that the file is the header file. For a description of the other file naming variables, see Table 5 .
The header file information created by GISMO for data subsetted and retrieved through GISMO is different than the header file obtained through the regular FTP access link. For an example of the header file information obtained through the regular FTP access link, refer to the Sample FTP Header File in this guide document.
The GISMO header file contains:
Note: The units in the GISMO header file indicate dd for grids described in decimal degree, and should not be confused with the units of the SNODAS variables such as m/1000. Those units are given in Table 1.
The following is a sample header file for data from GISMO that has been subsetted. Note: The actual values in the header file will be different depending on the region subsetted. Currently GISMO creates one sample header file per request unless the user requests GIS output for data in a format suitable for reading into GIS systems. In that case, GISMO creates one header file per data file.
Sample GIS header file for subsetted data from GISMO request #200961710189 units dd nrows 387 from GISMO Subset Grid Height ncols 421 from GISMO Subset Grid Width nbits 16 bytes per pixel * 8 *** Varies by file, may need to be changed *** byteorder M (big-endian) layout bil band interleaved - one band. ulxmap -107.07124 Upper left longitude in degrees ulymap 39.75375 Upper left latitude in degrees xdim 0.008333334 in degrees/pixel = mapscale ydim 0.008333334 in degrees/pixel = mapscale
For more information about setting options for GISMO output, see GISMO Help. If you have any questions, please contact NSIDC User Services.
Table 6 shows the size of uncompressed header and data SNODAS files, and compressed tarred and zipped archive SNODAS files for a sampling of data collected 2003-10-23. The total size of all files is also given. Compressed file sizes for other dates will vary depending on how many cells are snow covered.
The following is a sample FTP header file associated with the file us_ssmv11034tS__T0001TTNATS2003102305HP001.Hdr.
Note: This header information may be different than that provided if data are obtained through GISMO. Refer to the GISMO Header File Naming Convention section of this guide document for more information.
Format version: NOHRSC GIS/RS raster file v1.1
Data source: RUC2, NESDIS, etc.
Created by module: sm_products
Created by module comment: number BARD codes: 0000000018 BARD codes:
58131678 58131679 75931875 37109162 58131676 18681689 87298325 5777000
58131674 68726564 9160380 87295989 12222 92757697 90881019 88954851
88955144 12229
Created year: 2003
Created month: 10
Created day: 23
Created hour: 8
Created minute: 53
Created second: 21
Last modified by module: sm_products
Last modified by module comment: Not applicable
Last modified year: 2003
Last modified month: 10
Last modified day: 23
Last modified hour: 8
Last modified minute: 53
Last modified second: 21
Satellite data: no
Satellite name: Not applicable
Satellite channel: 0
Satellite data calibrated: no
Description: Modeled snow water equivalent, total of snow layers
Thematic: no
Theme file: Not applicable
Data units: Meters / 1000.000000
Product code: 96687381
Attribute table: Not applicable
Data file pathname: us_ssmv11034tS__T0001TTNATS2003102305HP001.dat
Data type: integer
Data bytes per pixel: 2
Data intercept: 0.000000000000000
Data slope: 1.000000000000000
Minimum data value: 0.000000000000000
Maximum data value: 504.000000000000000
No data value: -9999.000000000000000
Number of columns: 6935
Number of rows: 3351
Geographically corrected: yes
Projected: no
Projection file: Not applicable
Horizontal datum: WGS84
Horizontal precision: 0.008333333333333
Elevation above datum: no
Vertical datum: Not applicable
Vertical precision: 0.000000000000000
Benchmark column: 0
Benchmark row: 0
Benchmark x-axis coordinate: -124.729583333331703
Benchmark y-axis coordinate: 52.871249516804028
X-axis resolution: 0.008333333333333
Y-axis resolution: 0.008333333333333
X-axis offset: 0.003749999996645
Y-axis offset: -0.003750483193850
Minimum x-axis coordinate: -124.733749999998366
Maximum x-axis coordinate: -66.942083333334011
Minimum y-axis coordinate: 24.950416183471813
Maximum y-axis coordinate: 52.875416183470698
Start year: 2003
Start month: 10
Start day: 23
Start hour: 6
Start minute: 0
Start second: 0
Stop year: 2003
Stop month: 10
Stop day: 23
Stop hour: 6
Stop minute: 0
Stop second: 0
Compressed: no
Compression file: Not applicable
Number of color tables: 0
Color table 01 descriptor: Not applicable
Color table 02 descriptor: Not applicable
Color table 03 descriptor: Not applicable
Color table 04 descriptor: Not applicable
Color table 05 descriptor: Not applicable
Color table 06 descriptor: Not applicable
Color table 07 descriptor: Not applicable
Color table 08 descriptor: Not applicable
Color table 09 descriptor: Not applicable
Color table 10 descriptor: Not applicable
Color table 11 descriptor: Not applicable
Color table 12 descriptor: Not applicable
Color table 13 descriptor: Not applicable
Color table 14 descriptor: Not applicable
Color table 15 descriptor: Not applicable
Color table 16 descriptor: Not applicable
Color table 01 file: Not applicable
Color table 02 file: Not applicable
Color table 03 file: Not applicable
Color table 04 file: Not applicable
Color table 05 file: Not applicable
Color table 06 file: Not applicable
Color table 07 file: Not applicable
Color table 08 file: Not applicable
Color table 09 file: Not applicable
Color table 10 file: Not applicable
Color table 11 file: Not applicable
Color table 12 file: Not applicable
Color table 13 file: Not applicable
Color table 14 file: Not applicable
Color table 15 file: Not applicable
Color table 16 file: Not applicable
Histogram: no
Histogram file: Not applicable
The data represent snow cover in the contiguous United States, extending into Canada for certain drainage basins. The spatial coordinates of the area are listed below:
Northernmost Latitude: 24.9504 ° N
Southernmost Latitude: 52.8754 ° N
Easternmost Longitude: 124.7337 ° W
Westernmost Longitude: 66.9421 ° W
Figure 5 is an example of the SNODAS SWE field displayed as an image.
 |
| Figure 5. Sample SWE Output from SNODAS |
For data accessed via the FTP site, the grid is 6935 columns by 3351 rows; the grid size from data accessed and subsetted via GISMO will depend on the area subsetted. Grid values are 16-bit, signed integers (big-endian). The first value at (1,1) is the top-left corner of the array (NW corner in this context). The file is structured so that values are read across the rows. For example, the second value to be read would be the second column of the first row (2,1). Grid cells have a 30-arc second spacing (nominally 1 km on the ground). Model output and precipitation variables are point estimates for the center of each grid cell and not an areal estimate. However, for the purposes of hydrologic and snow cover forecasts, these point estimates are assumed to represent average conditions in each grid cell.
The x- and y- axis coordinates are listed in the header files (.hdr) associated with each data file. See a sample header file. The x-axis coordinate of the center of the upper left hand cell is given in the Benchmark x-axis coordinate, and the x-axis coordinate of the left edge of the upper left hand cell is given in the Minimum x-axis coordinate. The y-axis coordinate of the center of the upper left hand cell is given in the Benchmark y-axis coordinate, and the y-axis coordinate of the top of the upper left hand cell is given in Maximum y-axis coordinate.
The X-axis offset and the Y-axis offset in the header files are the distances between the origin and the center of the pixel that lays over the origin. The purpose of those parameters is to provide an easy way of confirming whether or not two grids are aligned, without regard to whether or not they occupy the same region.
SNODAS fields are grids of point estimates of snow cover in latitude/longitude coordinates with the horizontal datum WGS 84. Estimates of SWE and snow depth, as well as other parameters, have no real areal extent. Therefore, projecting SNODAS output to a particular projection may not be necessary. Moreover, different users prefer different projections. For example, federal agencies are likely to use the Albers Equal Area projection, while researchers may prefer an alternative such as one of the projections used for the Equal Area Scalable Earth (EASE-Grid). Refer to All About EASE-Grid for more information. Given that SNODAS outputs are essentially point estimates, the decision to project the data and choice of projection can be left to individual users.
NSIDC archives fields representing the model state for 06:00 Universal Time (UTC). The time 06:00 UTC was chosen because this is closest to midnight for the United States. Snow data are for 01:00 local time for the East Coast and 22:00 for the West Coast. SWE, snow depth, and snow pack average temperature represent the state of the snow pack at 06:00 UTC. Snow melt runoff, sublimation and evaporation, and precipitation parameters that describe sources and sinks of snow pack water are integrated for the previous 24 hours, giving daily totals. Note that output for 06:00 UTC is a best estimate of snow pack characteristics. Because SNODAS only updates snow fields once a day, 18 out of 24 time steps in each day's model run do not use observations to update model estimates. Therefore, hourly data from SNODAS is model output only and does not represent the best possible estimate of the snow pack.
NSIDC has scripts that run several times a day. If new SNODAS files are found, these scripts will automatically post them to our FTP server. If you need data sooner than the normal timeframe that NSIDC uploads files to our FTP site, you can contact NOHRSC, as they distribute the data for operational users.
NSIDC has not conducted an assessment of these data. For information, please refer to Barrett (2003), or contact NOHRSC.
Data are available via FTP. For subsetting options, please see the section on Subsetting Data Using GISMO.
Note: NSIDC cannot always post data as soon as NOHRSC makes it available. Occasionally one or more files are missing from the NOHRSC output. Generally, files are available from NSIDC within one day of production at NOHRSC. However, users should have no expectation that NSIDC will consistently have all files within one day of production. Occasionally, NSIDC does not receive data; thus, you should check the SNODAS Data Products at NSIDC missing files list to see which files are not available. Users needing files in a timely manner for operational use should contact NOHRSC directly to make arrangements.
For information on how to ingest SNODAS data into an image processing software such as ENVI, see Appendix B in the National Operational Hydrologic Remote Sensing Center Snow Data Assimilation System (SNODAS) Products at NSIDC Special Report.
The tarred FTP files can be opened with WinZip. When WinZip opens them, however, it corrupts the file and makes its size too large. To ensure that WinZip does not corrupt the files, apply a configuration option to WinZip by following these steps when untarring the .tar.gz files:
Note: These instructions may vary depending on which version of WinZip you are using.
GISMO is a tool that was developed by NSIDC for working with gridded data sets. Please note that you need to register as a GISMO user in order to obtain the user name and password necessary to log into the GISMO interface. After you have registered, you can select the SNODAS Interface link at the top of the GISMO Home page. You can subset the SNODAS data set by parameter, date, and spatial extent. For example, you might use GISMO if you want to order snow depth data for Michigan on a single date. See the Collection Summary
link
in the sidebar of the GISMO application for information on the characteristics of the SNODAS data in GISMO. For information regarding GISMO error sources, please see the Error Sources section of this document.
NOHRSC supplies NSIDC with files that only have the eight variables contained in this data set. No additional processing is done at NSIDC except for the renaming of the file extension. See the reference information on NOHRSC processing.
When ordering data through GISMO, the data set comes with a .pcf file, a .hdr file, and latitude and longitude files. However, the corners, the dx, and the dy of the latitude and longitude files do not agree with the stated corners, dx, and dy in the .hdr and .pcf files. There is a known problem with the GISMO subsetting tool where the backend processing cuts a rectangle out of the data and tries to calculate what the corner points should be. Originally, GISMO was designed to work with 25 km and 12.5 km data and the tool works fine calculating the corner points accurately. However, the SNODAS data is nominally 1 km data, which does not work as well in GISMO. Thus, NSIDC recommends that you use the latitude and longitude files instead of the .pcf file. However, there is still a slight discrepancy of approximately half a pixel between the .pcf file and the latitude and longitude files. It appears that GISMO is using the outside corners of the grid cells whereas the latitude and longitude files are referencing the center. Since 1 km is approximately 0.01 degrees, half a pixel would be about 0.005 degrees.
Barrett, Andrew. 2003. National Operational Hydrologic Remote Sensing Center Snow Data Assimilation System (SNODAS) Products at NSIDC. NSIDC Special Report 11. Boulder, CO USA: National Snow and Ice Data Center. 19 pp.
Carroll, T., D. Cline, G. Fall, A. Nilsson, L. Li, and A. Rost. 2001. NOHRSC Operations and the Simulation of Snow Cover Properties for the Conterminous U.S. Proceedings of the 69th Annual Meeting of the Western Snow Conference, pp. 1-14.
Carroll, T. 2005. Overview of the Center's Web Site and Products . National Operational Hydrologic Remote Sensing Center, 15 pp.
Jordan, R. 1990. User's guide for USA-CRREL one-dimensional snow temperature model (SNTHERM.89). USA Cold Regions Research and Engineering Laboratory (CRREL), 18 pp.
Visit the NOHRSC Web site for additional NOHRSC snow products and tools.
In Colorado, the Bureau of Reclamation and Colorado Water Conservation Board are assessing SNODAS for hydrological forecasting purpose. Visit the U.S. Department of the Interior Bureau of Reclamation Web site Snow Data Assimilation System (SNODAS) Colorado Data Plots and the Western Water Assessment for more information.
This data set and documentation were developed with the assistance of NOHRSC Director Thomas Carroll and NOHRSC staff, and NSIDC’s Andrew Barrett. The product team at NSIDC consisted of Lisa Ballagh, Florence Fetterer, Alejandro Machado, and Keri Webster. Ross Swick developed GISMO and the GISMO SNODAS interface.
Development and distribution of the data set from NSIDC is supported by funding from NOAA's National Environmental Satellite, Data, and Information Service (NESDIS) and the National Geophysical Data Center (NGDC).
Table 7 lists acronyms used in this document.
| Acronym | Description |
|---|---|
| EASE-Grid | Equal Area Scalable Earth |
| FTP | File Transfer Protocol |
| GISMO | Graphical Interface for Subsetting, Mapping, and Ordering |
| NESDIS | National Environmental Satellite, Data, and Information Service |
| NGDC | National Geophysical Data Center |
| NOAA | National Oceanic and Atmospheric Administration |
| NOHRSC | National Operational Hydrologic Remote Sensing Center |
| NSIDC | National Snow and Ice Data Center |
| NWP | Numerical Weather Prediction |
| RUC2 | Rapid Update Cycle 2 |
| SNODAS | SNOw Data Assimilation System |
| SWE | Snow Water Equivalent |
| UTC | Universal Time |
| WGS | World Geodetic System |
This documentation was written by Keri Webster and Florence Fetterer and is based on the publication National Operational Hydrologic Remote Sensing Center Snow Data Assimilation System (SNODAS) Products at NSIDC.
November 2004
18 June 2009: A. Windnagel updated the Grid Description section with information on the order of the array.
14 May 2009: A. Windnagel updated the File Naming Convention section that was missing some information, added information on opening the .tar.gz files with WinZip, added information on obtaining near-real-time data, and added a glossary.
07 August 2008: D. Miller updated guide doc with edits from Florence Fetterer and Andy Barrett.
01 April 2008: D. Miller reformatted and reorganized the guide documentation based on comments from User Services (Kara Gergely) to make the guide documentation easier to use. USO was receiving a lot of questions about this data set.
02 February 2007: F. Fetterer made the following changes: Added link to the Bureau of Reclamation and WWA Web sites, added units and product code to table, added information on using GISMO formerly found in the FAQ.
02 February 2006: F. Fetterer added links to a Frequently Asked Questions page authored by L. Ballagh.
22 December 2005: F. Fetterer added text describing the renaming of .grz files at NSIDC. Renaming was instituted in December 2005 for the following reasons: 1) .grz is not a standard data type or file extension, 2) The compression and storage of the files is accomplished by tarring each set and then compressing them using the gzip compression program. This has several recognized filename extensions, but the most prevalent is .tar.gz. Changing the extension to this more recognized format will help alleviate user confusion while at the same time not altering the actual distributed data files contained within the tarred file.
19 December 2005: F. Fetterer added text advising users needing data on an operational basis to contact NOHRSC.
09 May 2005: F. Fetterer added information on subsetting options.
http://nsidc.org/data/docs/noaa/g02158_snodas_snow_cover_model/index.html
