Precipitation Shapefile Download

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 hourly precipitation estimate for each HRAP grid cell.

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

At this time, data files prior to 2008 are unavailable from this page.

If you have any questions or problems, please contact SR-TUA.Precip@noaa.gov.

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 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. globvalue - 24-hour precipitation value in inches. "-1" values correspond to "No Data", e.g. data over the ocean. "-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.

About the Hourly Precipitation Analysis Pages

These pages graphically show the latest short-term observed precipitation across the majority of the National Weather Service (NWS) CONUS and Puerto Rico.

Observed Precipitation

"Observed" data is derived from output from NWS River Forecast Centers (RFCs) , and is displayed as a gridded field with a spatial resolution of 4x4 km. "Observed" data is expressed as a short-term duration total ending at the hour indicated in UTC (same as Greenwich Mean Time, or GMT). For example 1200 GMT coincides with 8 AM EDT, 7 AM EST, 7 AM CDT, 6 AM CST, etc.

When viewing "NWS" data, you may notice that "Observed" data extends beyond the U.S. border into Mexico. The West Gulf RFC has service areas that extend beyond the U.S. border, in order to model rivers that flow into the United States, (i.e. tributaries of the Rio Grande along the Texas-Mexico border.) Although no forecasts are provided outside of U.S. boundaries, precipitation estimates are created over these areas in order to simulate streamflow along these rivers as they cross into the United States. When viewing the data, it may be helpful to turn on the "RFC Boundary" overlay as a geographic reference.

Observation Methods

RFCs derive the "Observed" precipitation field using a multisensor approach. Hourly precipitation estimates from WSR-88D NEXRAD are compared to ground rainfall gauge reports, and a bias (correction factor) is calculated and applied to the radar field. The radar and gauge fields are combined into a "multisensor field", which is quality controlled on an hourly basis. In areas where there is limited or no radar coverage, satellite precipitation estimates (SPE) can be incorporated into this multisensor field. The SPE can also be biased against rain gauge reports.

Quality of Data

"Observed" data is vulnerable to inaccuracies that can be caused by either radar or precipitation gages. For radar, problems would include freezing or frozen precipitation, low topped convection, bright banding, the reflectivity/rainfall relationship in use, calibration of the radar, radar location and elevation, range degradation, and the radar's effective coverage. For precipitation gages, problems come from freezing precipitation, windy conditions, gage siting, under measurement by tipping bucket gages in high intensity rainfall, and gage maintenance.

Production / Update Times

The hourly precipitation analysis pages are routinely updated each hour, at approximately 50 minutes past the hour. The data for each hour are preliminary and subject to change, they are neither official nor certified. Please contact the National Climatic Data Center for certified past weather information.

Data Formats

The precipitation fields are provided in GIF format for viewing, and shapefile and netCDF formats for download and use in other projects and research. More information about using netCDF files is available from the University Corporation for Atmospheric Research (UCAR).

Other Useful Information

"How much rain fell, and where?" These pages help answer this question, but the real question is "How can I use this information to make decisions?" This page provides links to various National Weather Service resources that you may find relevant. The list is by no means exhaustive, so please visit http://www.weather.gov for more information.

• Local weather forecast by "City, St" or zip code:   
   
• Forecast Precipitation for the next five days
• Live Radar Imagery

• Advanced Hydrologic Prediction Service (AHPS) - Impacts of high water or flood, impacts of low stage or level, agricultural impacts, short-term and long-term hydrologic forecasts, water supply forecast

• Palmer Drought Severity Index
• Palmer Crop Moisture Index
• U.S. Drought Monitor
• Seasonal Outlook

• National Climatic Data Center (NCDC) - The world's largest weather archive, the only source for official, certified past weather data.
• National Weather Service Climate Pages - Drill down to the your local Weather Forecast Office for free past-weather information.

• The National Operational Hydrologic Remote Sensing Center (NOHRSC) is the definitive site for snow information from the National Weather Service. Using their Interactive Snow Information interface, you can browse through their suite of snow information, including snow cover, snow depth, snowfall total last 24 hours, and more.

• Water Supply Information from:
  • Arkansas-Red Basin River Forecast Center
  • Colorado Basin River Forecast Center
  • California-Nevada River Forecast Center
  • Middle Atlantic River Forecast Center
  • Missouri Basin River Forecast Center
  • North Central River Forecast Center
  • Northeast River Forecast Center
  • Northwest River Forecast Center
  • West Gulf River Forecast Center
• Fire Weather from the Storm Prediction Center
• Frost Depth from the North Central River Forecast Center

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