How do you measure rainfall?

General Discussions: ASK John: How do you measure rainfall?

By jack_in_ct on Sunday, July 27, 2008 - 09:03 pm: Edit Post

Out here in Connecticut we have been getting a lot of rain in the last few days. I saw a total today of 3.19 inches for the month of July and couldn't believe it. Based on the level in my pool we have received at least 5 inches this week (from near drought to flooding in some areas).
What do the weather people use to measure the rainfall? I figure if you have a little tubular rain gauge its level would go up the same as my 21 foot pool since they are both basically cylinders.


By admin on Monday, July 28, 2008 - 10:02 am: Edit Post

Most NWS offices use an automated rain gauge, but also have a manual one for backup/calibration.

With the manual ones, it is pretty straight forward, you have a collection container, usually a cylinder that collects the rainfall and there are graduations on the cylinder that indicate how much rain has fallen. Many collection containers have a smaller, inner container that is attached to a funnel at the top of the larger container. The smaller diameter makes it easier to measure the fractions of inches of rain that fall.

If you think your measuements are different from that reported, it could very well be true. Rainfall from thunderstorms can vary wildly from one locale to another, even in the space of a mile or two.

-John


By jack_in_ct on Thursday, July 31, 2008 - 08:29 pm: Edit Post

Thank you for the reply. Based on what you wrote I asked around and found out that they measure our local rainfall at the airport which is located right on Long Island Sound.
I live a few miles inland from there.
The guy I talked to said it is not unusual for the rain to basically go horizontal at the shoreline because of winds at various altitudes over the water and then fall inland as the trees and buildings break up the airflow. He said where he lives (a few more miles inland from me) he tends to get lots more rain and snow but less wind than what he sees at the airport when he makes his reports.


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