Rain gauge

[Spider-Vice]

I'm getting sick of my rain gauge in my Fine Offset. So I saw mods around here to increase its height so it doesn't spill in strong rain, so I did that mod. The first rainfall event went well, 24mm, all right. Now it's also been raining and other stations have nearly double of what I have, and it is raining and it takes so long to accumulate.
Probably my mod's height is too much. I don't have pictures at the moment. I was thinking of increasing the catchment area but I would need to know the dimensions of the rain gauge and probably the math to apply the correction on Cumulus, but that only after I've decided what to do... Suggestions are welcome. I will probably try to decrease the height of the anti-spill mod.

[NO0C]

Hi Spider-Vice,

The first thing I would do is move the sensor outside

24 mm ? Wow that's a lot of rain compared to this drought stricken area of the world.

I'm not sure what height has to do with accuracy, unless it's a wind issue.

What do you mean by spillage? Sensor won't take the rain fast enough. If that's the case, a larger catch area is really going to be a problem unless you throttle down the flow.

Increasing the catchment area and applying the math is a simple chore.

Compute the area of the new catchment = N

Compute the area of the old catchment = O

O/N = multiplication factor to apply.

Good luck.

Regards,

[Spider-Vice]

Yeah it's been raining a lot here. What I mean is that the FO's rain gauge is too shallow for strong rain, so it spills and readings are missed, so I increased its height a little bit to avoid spillage.

[Charlie]

It's hard to believe you could make it too high. Perhaps you could post a picture, and some numbers of measured vs. expected.

[Spider-Vice]

Measured vs expected I can give you now: 16mm vs 28. It's a huge discrepancy, it could have to do with the FO mucking up during this storm but I'm not sure. For now I can't give you pictures because I can't go to the roof, the shingles are wet.
It did measure surprisingly well in the first storm the mod passed through though!

[Charlie]

How is it mounted? It really should not be on the roof if you can avoid it.

You may have a bad reed switch. There is a failure mode where the switch will give about 1/2 the expected counts - I had this failure with my anemometer. Replaced the switch and all was well.

[Spider-Vice]

I live on a high building, I can only have it on the roof. Anyway it did measure well yesterday, when I can I'll try diagnosing that!

[BillW]

Hi,
This sort of issue seems to re-occur time and time again. I have had a few consumer grade tipping buckets and whilst they're definitely the most convenient they always seem to fall short.

If you have regular access to your roof space you could always consider an old fashioned measuring cylinder.

I seem to be saying this a lot recently but a few years worth of experience has shown me it is the way to go.

Sure it takes a bit of time but it's nice to go out and note down a reading, I find it put's you in touch with the weather more and at least you actually get to look at the sky whilst outside.

cheers,
B.

[Tau Bootis]

Hi

Your main problem is the location of the rain gauge.

It has been known for a few hundred years that the higher you site your rain gauge the lower the catch will be and wind is the main factor, if there is no wind your results will be more accurate.

There are many web pages on the subject here are just a couple
http://www.nws.noaa.gov/om/coop/standard.htm

http://www.nws.noaa.gov/om/csd/pds/PCU6 ... posure.htm

With regard to the height of your mod that should be OK and will prevent splash out but a tipping bucket will have its limits, once the rate at which the bucket can tip is reached any excess will be lost, this is where a manual gauge becomes very useful.

If you decided to increase the area of the funnel (as I have done) then the point at which it reaches its maximum rain rate will be reduced.

Trying to compare your readings with other local sites can be very misleading, I have a tipping bucket and two manual gauges one of which is along side the tipping bucket and the other 4 m away, sometimes all three are the same and sometimes all three are different.
At the end of the day you are measuring rain at the location of your gauge and nowhere else.
If you are considering getting a manual gauge and are on a budget then this cheap plastic one:

http://www.amazon.co.uk/Bosmere-k140-K1 ... 557&sr=8-2

was very accurate when tested over several months along side this more expensive one:

http://www.weathershop.co.uk/shop/tfa-4 ... naloutdoor