Tuesday, April 8, 2014

CoCoRaHS Observations Served Up on NWS Web Sites

CoCoRaHS observations are now accessible through an interface on National Weather Service office web sites.  The observations are available using a tool called NOWData (NOAA Online Weather Data) found under the Local Climate option on the web site menus.

The main left-hand menu on the NWS office home page (top), and the window showing the NOWData tab (bottom)

NOWdata has been a feature on NWS climate pages for a couple of years, but a recent upgrade added new capabilities and access to CoCoRaHS observations, data from Remote Automated Weather System (RAWS) network, data from the USDA SNOTEL network, as well as from the NWS U.S. Cooperative Network stations. RAWS stations are largely used in the western U.S. for fire weather support, so your area may not have nay RAWS stations nearby depending on where you are.

If you would like to look at data from the U.S Cooperative Network stations, choose a station from the list in the list box on the left-hand side.

NOWData menu for the NWS Lincoln, IL office

CoCoRaHS and RAWS data are only accessible through the map interface. To access the map, click the View Map button on the left-hand side of the window.  The initial map that displays will show the NWS County Warning Area (CWA) shaded with push pin symbols representing the U.S. Cooperative Network stations. If you hold your mouse over a symbol on the map the name of the station will display in the lower left corner of the map window.

To view the CoCoRaHS stations available (stations that have reported in the past year), click the "Show more stations" button at the bottom of the window.  The map will get cluttered, but you will see the CoCoRaHS symbols on the map. You can zoom in on an area by dragging/panning the area you are interested in to the middle of the window, then click on the "+" symbol as many times as needed to zoom into the area you want, or you can use your mouse wheel. Again, holding your mouse over a symbol will display it's name in the lower left hand corner of the screen. Click on a symbol to select that station.

The NOWData map window displaying U.S. Coop an CoCoRaHS stations

The data is available in tables and in charts. Since we don't record temperature as part of CoCoRaHS none of the temperature products will be relevant.  here are examples of the products using data from my CoCoRaHS station, IL-CP-1.

Daily data for a month is similar to the Station Precip Summary on the CocoRaHS web site.

Daily precipitation for the current month. You can list daily precipitation for any month in the record.

The Daily Almanac provides you with your statistics for today and the month and year to date, as well as record highest and lowest amounts and accumulations.

Daily Almanac product on NOWData

Monthly and annual summary product on NOWData.
Monthly Summarized Data is also useful. With this you can view your monthly totals, the daily maximum or minimum for each month, the mean monthly precipitation, and the number of days where precipitation is equal to a great than an amount you specify. However, one serious drawback to the monthly summarized data is that it does not currently include multi-day amounts.  When I first pulled up my data I was amazed at the number of "M"s (missing) appeared in the monthly totals. If data is missing for any day in the month, then the sum is set to missing, and if any month is missing, the annual total is set to missing. I do not have any days missing in my CoCoRaHS record. However, I have a number of multi-day accumulations, as many of us do. The underlying database for the NOWData tool does not at this time assimilate the multi-day amounts, so days included in a multi-day period are set to "M". I've been told that this should be resolved in the future. In the meantime, your can use the Station Precip Summary option on the CoCoRaHS web site to get your actual monthly totals.

Accumulation graphs can also be generated for a time period you specify. The graphs display the highest, lowest, and the actual data for the period you specify.  When you mouse over a data point on one of the lines in the chart it will display the data, observed precip, accumulation to date, and the highest and lowest accumulation for the period to date for the station selected.

Accumulated precipitation for 2014 for my CoCoRaHS station.

Accumulated snow fall for my station for the winter of 2013-2014.

Take some time to jump on to your NWS office web site and play around with NOWData. It's a pretty cool tool. Here is a link to a page which lists and links to all of the NWS offices by state:

NOWData - NOAA Online Weather Data


  1. Great information. Too bad it is so difficult to access. You cannot even bookmark it.

  2. There is only a representative sample of CoCoRaHS stations that I see in my area of the map

  3. Max, I'm not sure what you are trying to bookmark, but you -can- bookmark the NowData page.

  4. Trail Cam Photos, only CoCoRaHS stations that have reported in the past 12 months are shown on the map. Otherwise, the map in many areas would be cluttered beyond being useable.

  5. Maybe I misunderstood. The above article said "stations that have reported in the last year" but maybe its stations that have been reporting for an entire year, as I just started in October of 2013.

  6. If you have been reporting you should be on the map. May I ask what your station number is?