AHPS Precipitation Analysis
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30 Year PRISM Normals Have Been Updated

The precipitation images, shapefiles and downloads have been reprocessed utilizing the updated 1981-2010 PRISM normals. Read More...

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Downloading Gridded Rainfall Data

Last Update: 04/17/2014 0351 GMT

(1) Choose Format (2) Select Download (3) Select Product (4) Select Date (5) Press the "Download" Button







General Information

The precipitation data are quality-controlled, multi-sensor (radar and rain gauge) precipitation estimates obtained from National Weather Service (NWS) River Forecast Centers (RFCs). The original data are in XMRG format and projected in the Hydrologic Rainfall Analysis Project (HRAP) grid coordinate system, a polar stereographic projection true at 60°N / 105°W. Our software reads each participating RFC's XMRG file and grabs the 24-hour precipitation estimate for each HRAP grid cell.

Use the form above to download these files. Alternatively you can download a program called wget that mimics ftp capability. Due to increased web security, the anonymous FTP server is no longer available.

If you wish to use wget (see above), shapefiles are stored at:
http://water.weather.gov/precip/p_download_new/

If you have any questions or problems, please contact AHPS.Precip@noaa.gov.

Metadata

The following links provide more information about the observed precipitation, normal precipitation, and derived precipitation products:

Shapefile Information

The shapefile contains the following fields:

  1. id - a unique value for each grid bin
  2. hrapx - column number of the HRAP grid cell (higher numbers are further east)
  3. hrapy - row number of the HRAP grid cell (higher numbers are further north)
  4. latitude of the HRAP grid point
  5. longitude of the HRAP grid point
  6. globvalue - 24-hour precipitation value in inches. "-2" values correspond to "Missing Data", e.g. an incomplete dataset.

The second download option "Legend File" will help you reproduce the color scheme we are using. If using Arcview, you will need to copy it into your c:\esri\av_gis30\arcview\legend_avl\ directory and load it manually through the legend editor. This file does not change from day to day.

Worldfiles (.GFW extension) and Projection files (.PRJ extension) are available at:
http://water.weather.gov/precip/p_download_new/metadata/

Please note, grids with no precipitation (i.e. 0.00") are not in the observed data shapefiles. A shapefile with all points is available at http://water.weather.gov/precip/p_download_new/nws_precip_allpoint.tar.gz.

A precipitation data legend file can be downloaded at

http://water.weather.gov/precip/p_download_new/nws_precip_legend.avl

A problem was discovered on August 9, 2007. The shapefile coordinates for each HRAP grid were indicative of the lower left corner of the grid rather than the center of the grid. The entire shapefile archive has been updated to correct the lat-lon issue. The shapefile http://water.weather.gov/precip/p_download_new/nws_precip_allpoint_conversion.tar.gz shows both the old and new coordinates for each point.

netCDF Information

The two netCDF files (one for CONUS, one for Puerto Rico), may be used independently of one another. Each file contains the following fields:

  1. hrap_xor and hrap_yor - the lower left corner of the grid
  2. hrapx and hrapy - grid dimensions
  3. amountofprecip - an array with the 24-hour precipitation values in hundredths of a millimeter (a value of 2540 corresponds to 1 inch). "-1" values correspond to "No Data", e.g. data over the ocean. "-2" values correspond to "Missing Data", e.g. an incomplete dataset.
  4. other metadata - date and time of creation, lat-lon of the bottom-left, bottom-right, top-right and top-left corners of the grids, et al.

NOTE -- Latitude and Longitude are not explicitly stated in the netCDF file. The second download option "HRAP-to-LatLon" contains source code for a C-program. The program contains a function that reprojects HRAP coordinates to Lat-Lon coordinates. The fully compiled program reads the netCDF files and writes ascii files with the following fields:

  1. id - a unique value for each grid bin
  2. hrapx - column number of the HRAP grid cell (higher numbers are further north)
  3. hrapy - row number of the HRAP grid cell (higher numbers are further east)
  4. latitude of the HRAP grid point
  5. longitude of the HRAP grid point
  6. value - 24-hour precipitation value in inches

To compile the C-program you will need to install the netCDF library on your computer. More information about using netCDF files (including the netCDF C-library) is available from the University Corporation for Atmospheric Research (UCAR).

   

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Page last modified: 26-Mar-2014 2:24 AM
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