Topic: Precip Rate 0 in/hr even though its raining

[nincehelser]

Truly “instant” readings are not possible with tipping buckets.



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[Mapantz]

Truly “instant” readings are not possible with tipping buckets.



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It's about as close as you can get with a PWS. As soon as the second tip occurs, you have your rain rate. As I mentioned in my last post, my rain rate records are almost identical to radar reflectivity at that point in time.

[galfert]

Truly “instant” readings are not possible with tipping buckets.



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I respectfully disagree.

A tipping bucket is doing nothing more than measuring a specific amount of water and counting each tip as a 0.01 inches. Count the number of tips in a given amount of time and you can project the instantaneous rain rate. Not any different than how a car calculates its instantaneous speed by each revolution of a wheel. Same exact principle. The water amount is constant and known 0.01 inches and the circumference of the wheel is known.  Which is why you can't change wheel/tire size without throwing the whole calibration off. Much like you can't change the size of the tipping bucket or diameter of the rain funnel as that would also have you needing to recalibrate.

A car's speed is nothing more than it's projection that if you were to keep that constant rotation of wheel spins per given time frame, it yeilds how far you'd travel in 1 hour. Rain rate is the same thing. If it keeps raining at that rate how much would fall in the next hour. Hence instantaneous rain rate. Same as car speed. How often the calculation is made does not matter. The more frequent the better. Take speed at every wheel revolution and rain rate at every tip and you have the lowest and best granularity possible for greatest accuracy. All weather stations measure at 0.01 in (or 0.2 mm) so they can yeild the same exact results.

Different weather stations report to the console at different intervals. But that doesn't matter. No rain is lost. You just apply the proper time frame into the measurement calculation. Much like I can measure a car's speed by timing distance traveled over time. I decided to measure car speed in my neighborhood. Without a radar gun I did it by measuring a point from one tree as a marker to another. Knowing this distance all I need now is a stopwatch and I can know other car speeds. So the reporting time doesn't mater. If I make it longer distance then the time is longer. If you don't report at the exact moment of every tip doesn't mater you then report at 2 tips. Changing the number of tips is like changing the measuring distance. What matters is to keep a known distance or in the case of rain a constant amount of water.

I could likewise change my car speed determination method by keeping my timing interval set to a specific reporting interval. Say for example I use 10 seconds. Then after those 10 seconds I count the number of wheel revolutions, but that is not practical so I can accomplish the same thing and instead measure the distance traveled. In this case I'm keeping measuring time constant. That would be more analogous to the weather station and the results are the same. You learn the speed or rain rate. Same exact principle. If I only have a yard stick without markings then I lose some precision. But if I have a yard stick with markings then I gain precision. Either way speed or instantaneous rain rate is just a projection of what is to come if things stay constant.

[nincehelser]

Don’t need your lecture.

It’s a discontinuous function.



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[nincehelser]

Truly “instant” readings are not possible with tipping buckets.



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It's about as close as you can get with a PWS. As soon as the second tip occurs, you have your rain rate. As I mentioned in my last post, my rain rate records are almost identical to radar reflectivity at that point in time.

“About as close as you can get” is true. 



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[WSWeather]

It’s a discontinuous function.

Unless you measure flow with a continuous electronic sensor I'm not sure what *isn't* a discontinuous function.

[galfert]

Don’t need your lecture.

It’s a discontinuous function.



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I thought we were exchanging in dialog. A lecture is one sided.

f(x) = tips * 0.01 * 6
Where tips = number of gauge tips within the last 10 minutes.

Seems pretty straightforward to me. Looks like I can graph it and plot points and then extrapolate and connect these points. Same as what is done with temperature.

[nincehelser]

Tips aren’t continuous.


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[nincehelser]

It’s a discontinuous function.

Unless you measure flow with a continuous electronic sensor I'm not sure what *isn't* a discontinuous function.

Which what you need if you want an instantaneous reading.


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[WSWeather]

It’s a discontinuous function.

Unless you measure flow with a continuous electronic sensor I'm not sure what *isn't* a discontinuous function.

Which what you need if you want an instantaneous reading.


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And you won't get it unless you're willing to spend well over $1,000 for a rain sensor.  Not really practical for a PWS hobbyist, and even then they're only accurate to around +/-10% so I'm not sure why a calculation using time and volume is any less valid.

[galfert]

Tips aren’t continuous.


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Tips are continuous because they represent the amount of water that is continuous. You can infinitely divide the amount of water.

If one tip increases the amount of water from some quantity A to B and a second tip increases the amount of water from B to C then the tips are continuous. You could also divide a tip into half a tip or a quarter of a tip and so on because it would change the amount of water by some divisible amount. Just because the tips seem to happen in whole tips is inconsequential for proving that tips are divisible if you wanted.

A dozen eggs is not continuous but if you scramble the eggs then they are continuous. If a hen lays lays 3 eggs in 3 days then the rate is 7 eggs a week. We can make that assessment very simply. Some days the hen may not lay an egg but that doesn't matter as the rate is just an assumption that if the rate continued it would be 7 eggs in one week. You can still have a function for hen egg laying rate and you can graph it. And we are basically scrambling the tips when they tip.

Therefore continuity is irrelevant to the fact that we can assess a rate to rain fall which is measured in determined set amounts just like speed is measured in set amounts that is the diameter of the wheel.

This is all simple Calc 1 stuff. I'm not a mathematician but I went through Calc 2. What's next talking about limits to prove that speed or rainfall is continuous. I'm not interested. At this point I feel that you are being argumentative for the sake of it.

[nincehelser]

Is am not interested in “discussion” with you either. 




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[lightmaster]

Both are valid methods for measuring rain rate. A better question is which is more useful. If you're in the middle of a storm, you'd care more about how hard it is raining at that particular moment, is it pouring out there, or has it let up to a drizzle. In this case, the (nearly) instantaneous rate is more important since it tells you how hard it is raining at that moment.

On the other hand, after a storm has passed, how much it rained at any one moment is less important. Now the amount of rain per hour is more important.... however, with such a long time frame for measuring, the usefulness of "how much rain did it rain per hour" more closely resembles the total rainfall.

Taking galfert's car analogy, which is more important to someone watching you drive, how fast you're going at that moment, or a summation of the total miles/kilometers you've driven in the past hour. "I'm sorry officer, I know your radar says I was going 60mph in a 45mph zone, but I've only been driving for 10 minutes so really I've only gone 10mph so far this hour".

[nincehelser]

It’s a discontinuous function.

Unless you measure flow with a continuous electronic sensor I'm not sure what *isn't* a discontinuous function.

Which what you need if you want an instantaneous reading.


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And you won't get it unless you're willing to spend well over $1,000 for a rain sensor.  Not really practical for a PWS hobbyist, and even then they're only accurate to around +/-10% so I'm not sure why a calculation using time and volume is any less valid.

No disagreement there.  Like I said, you aren’t going to get “real” instantaneous values on tipping bucket hardware.

Rain rate is bit more difficult subject than some people realize.  That’s why wunderground set their protocol and method to give comparable results among differing hardware.  It’s not perfect, but it does well enough.


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[Carbon]

Back to the original topic - WU is certainly rounding to the nearest inch on the new layout. It's really a shame that I have to go to the old layout to get any sort of useful rain rate data. When I passed 0.5 in/hr it went to 1 in/hr. Anything less than 0.5 in/hr shows as 0 in/hr. Here's to hoping it gets fixed soon.

[lightmaster]

Back to the original topic - WU is certainly rounding to the nearest inch on the new layout. It's really a shame that I have to go to the old layout to get any sort of useful rain rate data. When I passed 0.5 in/hr it went to 1 in/hr. Anything less than 0.5 in/hr shows as 0 in/hr. Here's to hoping it gets fixed soon.

Whoever thought to have inches of rain as a whole number has never dealt with weather information before. Honestly though, I prefer the old pws pages and hope they don't get rid of them.

[Carbon]

I'm guessing it might have been a lazy webpage coding sort of thing (treat every value the same way) and not necessarily that they thought rounding to the nearest inch for rain rate was a good idea. With the nature of rain rate, rounding to the nearest inch makes it almost useless. I recall reading a post at some point saying they won't shut off the old site until they fix the outstanding issues, but that it will be gone eventually.

But hey, look on the bright side... at least they're not rounding 30.44 inHg to 30 inHg...

[lightmaster]

I recall reading a post at some point saying they won't shut off the old site until they fix the outstanding issues

That's good, it'll never go away then.

[Bswartz95]

Just found this topic.

I've been trying to make sense of my rainfall rate.  It seems to go up with total rainfall once an event begins.  Also, after the event ends, the rainfall rate slowly decreases to 0.00" over an extended amount of time.   According to what I'm reading in this thread, that is normal for AcuRite (Atlas), as they do NOT display instantaneous rainfall rates?

My neighbors, who have a Davis PWS shows over 2.00"/hour in a heavy storm, but my Atlas rate goes up incrementally (see pic).  Just a different way of recording rates?

[galfert]

According to what I'm reading in this thread, that is normal for AcuRite (Atlas), as they do NOT display instantaneous rainfall rates?

Seems to me like you are understanding the concept perfectly.