Java Precipitation Map Information

Of the hydrological and meteorological variables routinely available, daily rainfall and snowfall totals are of perhaps greatest interest to a wide range of users outside the hydrologic community. As with many scientific products, their utility is determined to a large extent by their timeliness and accessibility. Daily precipitation totals (measured from 1200 UTC to 1200 UTC) are available from approximately 3000 stations that report hourly precipitation totals in the HADS data stream, and from an additional 4000+ stations that report daily totals only.

We thank Mike Baldwin and Sid Katz of the National Centers for Environmental Prediction for his help in accessing the data displayed in this web site.

About the Java applet:

The overview window:

The show overview button on the applet reveals or hides a small window showing a national map. The region shown in the main applet window is indicated as a rectangle in the overview window. You may move the rectangle in the overview window by dragging with the mouse. The rectangle's new location will be reflected in the main window shortly after you release the mouse button (1-2 seconds on my 166 MHz machine). Tip: if you lose track of the overview window, try clicking the overview button twice. Another tip: you can always use the reset button of the applet to bring the map back to its initial configuration (while still showing the currently loaded data).

Daily total precipitation data:

These data are shown as color coded values on the map, and as numerical values near the cursor. Values are in inches. Stations reporting every hour are shown with solid symbols; stations with missing hours are shown with hollow symbols. For stations in the daily data stream, we show the values as they are reported to GSD. For HADS data, the daily total is the sum of the hourly values received.

Map backgrounds:

The map consists of 325 state boundary segments, 537 river segments (at 15 km resolution), and 3860 county boundary segments (at 20 km resolution). These segments, originally in latitude/longitude coordinates, were remapped to Lambert's conformal conic projection, tangent to the globe at 20 degrees north latitude, and centered at a longitude of 95 degrees west. Points on the segments were coded as 2-byte signed integers in the range 0 to 32000, where the point (0,0) is the upper left hand corner of the map. We call this coordinate system 'java-conus-1'

Station Information:

The format of the file containing station information (station_info.bin) is as follows:

1. number of characters in station name = n_name (1 byte)
2. station name (n_name bytes)
3. x,y location in the java-conus-1 coordinate system (signed short, 2 bytes each)
4. number of characters in description = n_disc (1 byte)
5. station description (n_disc bytes)

Data files:

The Daily data, HADS daily totals, and HADS time series' are stored in separate files for each day.

The format of the daily files (suffix .day.bin) is as follows:

1. index to the station information (signed short, 2 bytes)
2. check character (4th char of station name) (1 byte)
3. tot rain reported in period (signed short, 2 bytes)

The format of the HADS totals files (suffix .3t24.bin) is as follows:

1. index to the station information (signed short, 2 bytes)
2. check character (4th char of station name) (1 byte)
3. tot rain reported in period (signed short, 2 bytes)
4. number of reports in period (signed short, 2 bytes)
5. index to the time-series data, or -1 if no time-series data exists (signed short, 2bytes)

The format of the HADS time series files (suffix .3ts.bin) is as follows:

• For the case when total reported rain > 0,
  1. number of reports in period (signed short, 2 bytes)
  2. for each hour reported:
     1. hour (1 byte)
     2. rain in hundredths of an inch (signed short, 2 bytes)
• For the case when total reported rain = 0 AND the number of reports is less than 24,
  1. minus the number of reports in period (signed short, 2 bytes)
  2. for each hour reported:
     1. hour (1 byte)
• (For the case of 24 reports and no rain, no time series record exists.)