Description

National Weather Service River (NWS) Forecast Centers (RFCs) use areal extent of snow cover products developed at the NWS National Operational Hydrologic Remote Sensing Center (NOHRSC) to help with lumped model calibration. Using CD-ROMS provided by NOHRSC, we have extracted snow cover data over the DMIP 2 Sierra Nevada basins during the prescribed DMIP 2 calibration period. The grids are snapshots of available days during 1990 to 1997.

This page provides grids clipped by the latitude longitude rectangle [-122W, 37.5N, -119W, 40N].

The cells in the grids provided contain one of three values:

50 = no snow
100 = clouds
250 = snow

Click here for more information about how NOHRSC derived these images.

Downloading the Data

Gzipped ASCII files are downloadable from three different directories on our ftp site (1990_95, 1996, 1997). Click here to obtain data from ftp site.

The same data are available in JPEG format. Click here to obtain the JPEG images of these files zoomed in on the American and Carson basins. The images show snow covered areas (green), cloud covered areas (gray), and areas with no snow or no clouds (white). Areas with missing data are black. The images also show the elevation contour used by the RFC to split the basins into zones in their modeling. The elevation splits for the American and Carson respectively are 1500 m and 2100 m.

File Format and Coordinate System

The data grids are provided in geographic (latitude/longitude coordinates). All files are provided in a gzipped ASCII format. The first several lines of the ASCII files give spatial reference information such as:

    nrows = number of rows
    ncols = number of columns
    xllcorner, yllcorner = coordinate for the lower left corner of the lower left cell
    cellsize (units are decimal degrees)
    NODATA_value

Data following the header information are listed in row-major order with the top (northernmost) row on the first line.

For users of ESRI software, data can be imported into Arc/Info using the "asciigrid" command or imported in to the ArcView Spatial Analyst using the File --> Import Data Source option.