How Accurate Is Your Rain Gauge?

Rain Gauge Discrepency

It isn’t uncommon for us to see spotty heavy rain across the area.  But often I will get people that E-mail and say “Hey, why are you reporting 1.5″ when I got over 3″ of rain in my rain gauge.”  I often attributed it to either a locally heavy rain, or maybe someone forgot to empty it.

Well, my father asked me to explain a very puzzling situation he has going on at his place.  He has a tipping bucket rain gauge on the roof of the house with his little weather station (yes weather runs in the family.)  The tipping bucket has nothing overhead, but a tree to the west that could potentially block a rain that is blowing in a wind from the west.  Combine that with tipping buckets under reporting rainfall in extreme heavy rain situations, I would expect it to run a little low. In addition, he also has two traditional rain gauges on the mailbox post.  One rain gauge is round and the other is like a quarter circle.  Look at the picture below to see how it looked after a recent heavy rain.

Rain Gauge Discrepency

The tipping bucket rain gauge on the roof measured 1.6″.  But the circular one measured 2.5″ with the other one measuring about 3.5″.  Both for sure were empty before the rainfall.  The official rainfall was 1.22″ for the city.  I want to point out that this isn’t a one time occurrence, but this is how things go every heavy rainfall that falls there.

This one has me perplexed. I checked to make sure the rain gauges were measuring properly and both are.  For the next rainfall I want to set a video camera up to watch and see if something changes.

Any thoughts people might have on what could cause this would be appreciated, because I for the most part am stumped.  If I can get video and figure it out, I will be sure to share!

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