# Meteorology question - rain accumulation measurement

It’s raining here. Hard. I look on the deck, and several water dishes that were dry are now nearly brim-full.

My question: If a straight-walled open container accumulates ‘X’ inches of water, does it mean that ‘X’ inches of rain fell? If not, what constitutes a good eyeball method of measurement?

That’s what it means. Right there over the top of the container that’s how much rain fell. In your case there might be some splashing from your roof though, best practice is in an open area or top of a building. You also have to know when they were dry to determine the time period that rain fell, or at least mark the previous water level from some known time.

Or get a rain gauge.

Official meteorological precipitation measurement is most often done by tipping bucket rain gauge. That means that the official measurement isn’t “collect rain in a straight-sided measured jar”, it’s “funnel precipitation into a tipping bucket device such that each .01” of fallen liquid precip flips the bucket from one side to the other, triggering an electrical pulse, and have the computer count the pulses."

But that’s still a low-maintenance proxy* for “how much has accumulated in this calibrated container?”

*“low-maintenance” because you have to empty out a container, whereas tipping-bucket meters are self-emptying – once you’ve measured .01" of liquid in the tipping bucket, the bucket empties onto the ground. No more observer going out to the gauge, reading it, and manually emptying it out.

Huh. So then - It’s raining harder than I thought. The dishes were emptied and dry after the dogs’ last romp last night at around 11pm. By noon today, they’d accumulated approximately two and a half to three inches. (they’re well away from the roof overhang) Not scientific, but useful in a kind of non-useful way.

Thanks!

Note that most actual dishes aren’t straight-sided. If the bottom is at all narrower than the top, then the depth will be greater than the rainfall measurement.

There are three - two which taper, one which doesn’t (it’s technically a cassarole dish). The tapered dishes were indeed more full (they also have greater capacity). The one with the most taper (~30 degrees) is quite full.

And people think the geometry they learned in school isn’t going to come in handy!

Dennis

Splatter can affect the accuracy of your dishes … one way around this is to install a funnel at the top of the container … just remember to calibrate the system … if the funnel has the same opening diameter as the inside of your container … then it’s a simple one-to-one conversion … but if your funnel has twice the area at it’s opening, then your container readings will need to be multiplied by two …

Or if you live in the Pacific Northwest … just count how many times you have to empty your 5-gallon buckets … I think I’m up to seven times this winter already …