Introduction

Gridded hourly precipitation files for the period of January, 1987- Dec 2002 are produced from daily, hourly Coop stations and SNOTEL data. Hourly gridded precipitation are produced using three data sources for the period of 1987-2002: 1) hourly cooperative observer (coop) gauges, 2) daily total coop gauges, and 3) SNOw pack TELemetry (SNOTEL) daily precipitation gauges. The daily values are disaggregated to hourly using the nearest hourly gauge values. The list of all stations used is provided in Table 1. The hourly values, expressed as fraction of normal, are then interpolated to approximately 4-km Hydrologic Rainfall Analysis Project (HRAP) (Greene and Hudlow, 1982) grids using an inverse-distance method. Finally, Parameter-elevation Regressions on Independent Slopes Model (PRISM) (http://prism.oregonstate.edu/) monthly precipitation climatology grids are used to compute fractions of normal at gage locations prior to the inverse distance interpolation and to convert interpolated fractions of normal to precipitation amounts at each grid point. The quality of this product is tested by comparing the mean areal precipitation from operational time series to the mean areal precipitation generated from the grids provided here. In addition, the derived data were run through a hydrologic model to verify that a reasonable water balance is achieved. A description of the methodology and the test is provided in Moreda et al. (2006).

Data Description

Times step: hourly
Unit: stored as hundredths of mm in xmrg files
Period January 1987- December 2002
Pixel resolution 1 hrap
File format: xmrg
Files are compressed using the Unix compress command.

The precipitation data cover the two basins (NF American River and The EF Carson River basin). The extent in HRAP coordinates is:

ncols 48
nrows 39
xllcorner 61.0
yllcorner 429.0
cellsize 1.0

A pdf file (sierra_nevada_data_extent.pdf) is available to illustrate the spatial coverage of these precipitation data relative to the basin boundaries.

A Shapefile of the HRAP cell centers converted to latitude-longitude coordinates is also available for reference:

snhrappts_ll.tar

Note that in the attribute table for this Shapefile only the HRAP integer ID is listed (lower left corner of the cell). The points in the Shapefile are actually located in the center of the cells so the lower left point in the shapefile is located at (61.5, 429.5) and the latitude/longitude listed in the attribute table also corresponds to the cell center.

Each hourly file is saved in XMRG format. Files from different years are stored in different directories. Click here to obtain data from ftp site.

Information on how to read and georeference xmrg files.