National Weather Service United States Department of Commerce

CoCoRaHS (pronounced KO-ko-rozz) is a grassroots volunteer network of backyard weather observers of all ages and backgrounds working together to measure and map precipitation (rain, hail and snow) in their local communities.  By using low-cost measurement tools, stressing training and education, and utilizing an interactive website, the goal is to provide the highest quality data for natural resource, education and research applications. 

Why do you need to know how much precipitation fell in my backyard?

Even in the day and age in which we live with Doppler Radar scanning the skies and automated weather observing equipment in many communities, we still need humans manually measuring the precipitation in their backyards.  These manual observations serve as ground truth for the precipitation estimates we get from Doppler Radar and automated station measurements.  Manual observations also fill in gaps where automated equipment doesn’t exist.  Plus, there are no automated instruments in our region that measure the snow.  So, we rely heavily on manual human observations to know how much snow fell.

Here’s a recent example of how rainfall varied across the “Metro Valley” between Huntington and Charleston. 

Even though we have several CoCoRaHS observers in this heavily populated area, even more are needed to accurately map the rainfall.  In more rural counties of our region, we often have no observers at all.

How do I become a CoCoRaHS observer?

Contributing your precipitation measurements each day takes less than 5 minutes (there’s even an app for that!) and it’s a fun way to learn about the wonderful natural resource that falls from the sky.  Here’s how to join and start sharing your precipitation measurements:

  • Obtain a high capacity 4” diameter rain gauge and place it in a convenient to access and unobstructed location. 
  • Take a short training delivered online.
  • Start taking precipitation measurements each day, preferably around 7 am and entering your measurements either via the website or mobile app.
    • You may be wondering why we ask you to take your precipitation measurements at 7 am?  That’s the time when forecasters compile all of the precipitation measurements received over the prior 24 hour period from human read and automated gauges.  Among it’s many uses, this data is analyzed and used to quality control radar precipitation estimates, helps forecasters understand which areas are more or less prone to flooding if additional rain is expected, and assists hydrologists with river forecasting.  If 7 am doesn’t work for you, you can still participate and enter your precipitation measurements when it’s more convenient for you.   

Have additional questions or want to learn more?

The CoCoRaHS website is a great resource to visit in order to learn more about the network and to look at precipitation measurements being collected right now across our region.  Each state has coordinators that can also help answer any questions you may have.  Links to these contacts are included below: