Rain Gauge- inaccuracy

[Jimmy1234]

I have a wh 1088 station and it seems to be behind in rain recording.
I've looked through some of the other threads on this issue, last night my rain sensor registered 6.0mm of rain and my towns weather station registered 11.6mm and i only live about 0.5 a Km away. now i realize it wont be the same reading not being side by side, but with the town one registering nearly double what mines logging dosent seem right. it was a steady rain and virtually no wind while it was actually raining, only pre.

I've mounted it about 1m above my roof. will i have to extend the sides somehow to make it catch more?

Any advice appreciated,

Cheers

[nking]

How long has it been on the roof, is it clean inside?

[Jimmy1234]

Yeah brand new at xmas, i've since checked (3-4 days ago) it and nothing at all inside.

[Ned]

Building up the sides will help. A rooftop collector is not ideal due to wind carrying rain past it - official gauges are mounted close to the ground to reduce wind effects. May not have been a factor in your last reading, but it will affect you in future. I suggest you obtain a cheap manual rain gauge and compare readings over time and use the calibration facility in Cumulus to get a reasonable agreement.
BTW, you're not in Gore are you?

[wd40]

Seems like we focus on the wind sensor more than we should leaving the other sensors in less than perfect setting.

The best thing I ever did was mount everything on a short steel post. That gave me a chance move it around while watching it in action with wind and rain as well as an occasional shake and thump. At the end of playing around with it I knew just what I wanted in a mounting set up. Once installed I zeroed out everything to start fresh.
Here some of the things I learned.

The rain gauge needs to be checked often for debris.
The distance from the ground for the temperature measurement is much more critical than I would have thought.
You need a good solar shield.
Swaying mast trips the rain gauge.
Extending the sides up on the rain gauge really helps.
You will loose sensor contact sooner or later.
Freezing rain freezes wind sensors.

Randy

[MickinMoulden]

will i have to extend the sides somehow to make it catch more?

Any advice appreciated,

Cheers

Only make it catch more if it's meant too. And you will need to know how much by.
You can make it "hold" more by increasing the wall height so that no rain bounces out (100mm will do). But you will need to make sure it is accurate before you do this. What is the catchment area? And what is it's minimum measurement (eg. 0.3mm, 1mm)?

[Super-T]

Are you sure that your town's rain gauge is correct?

[MickinMoulden]

Are you sure that your town's rain gauge is correct?

Excactly! All you can do is make yours the best it can be, or as accurate as can be then you'll know who is: (a) getting accurate results and (b) who's getting more or less rain. So, what's the measurements of the collector?

[wd40]

I extended my sides straight up 2" using aluminum tape so the area is still the same. So far, it is dead-on. Before I added the sides it fell behind the manual rain gauge about 10%.

Randy

[Station House]

Hi - there are a number of threads on here where people have 'adapted' the rain gauge by fitting a funnel - beleive you then need to calculate the increased collection area (good old pi from school maths!) and recalibrate in cumulus

If I can see a thread I'll attach a link - there again Gina might get there before me!


Try this link:

https://cumulus.hosiene.co.uk/viewtopic.p ... nel#p23251

There are others if you search on 'rain gauge' in the forum

[Jimmy1234]

Building up the sides will help. A rooftop collector is not ideal due to wind carrying rain past it - official gauges are mounted close to the ground to reduce wind effects. May not have been a factor in your last reading, but it will affect you in future. I suggest you obtain a cheap manual rain gauge and compare readings over time and use the calibration facility in Cumulus to get a reasonable agreement.
BTW, you're not in Gore are you?

Yep, i'm in gore ned, um i guess its a standard rain gauge with the see saw type arrangement, 0.3mm per closure, i'll probably build the sides up a bit on it like alot of people say. I've bought a nylex 120mm manual rain gauge today and mounted it just across from the electronic one, suppost to get rain tomorrow night so i'll see what the story is then, if theres a difference, the met service one could be wrong who knows..

Cheers

[m0clx]

I have fitted a cheap funnel (diy store) and an upside down plant pot with the bottom cut out. It has increased the collecting area a bit so I use a correction factor 0.7 (calculated this - difference in areas) and it seems pretty spot on. I think the original 'bucket' value of O.2 mm is ok, but with the shallow sides most of the water is blown off or sticks as rain drops which evaporate quickly!
The sensor is quite sensitive to being shaken - so the mast needs to be stable in high winds.
If in doubt take the lid off and flick the bucket over - it should register on the rain guage display.
G

[alexgray]

We had the opposite problem - recorded two ridiculous bursts of rain this afternoon totalling about 190mm!

Studying the daily graph I think I have the answer. I think that wind gusts (up to 65 mph today) must have shaken the rain sensor so violently that it has recorded as if lots of water were passing through. Looking at the detailed logs of wind and rain, the two massive peaks in apparent rain correspond exactly in time with the two highest wind peaks of the afternoon.

So I think the rain sensor mount needs stiffening a bit. I may also reduce the rain data to the average of the two other nearest stations to avoid a blip that is otherwise big enough to distort our monthly figures strongly.

It worries me know that our readings in other stormy periods may have been significantly too high, but not so much as to be so obvious as today's. Maybe your town gauge had the same problem.

Alex

[Ned]

So I think the rain sensor mount needs stiffening a bit.

Best if you can screw the rain gauge down onto something solid. It has a lug at each end for that purpose.

[mr.sneezy]

So I think the rain sensor mount needs stiffening a bit.

Best if you can screw the rain gauge down onto something solid. It has a lug at each end for that purpose.

I'd second that too. If you can shake your rain gauge mounting and get an increased reading on the display then it's not solid enough.
I've had a virtually identical looking three reading rain gauge on the apex of my shed roof for some years, and never got one false reading mounted that way. When I fitted the new one on from the WH2081 kit to my TV mast I got false reading right away (wind swaying it). Had to move it right to the bottom of the pole near the gutter.

Hey while I'm here, this stuff about building up the sides of the rain gauge with tape or similar. Why does that not seem to be necessary on the standard round manual gauges like the official government ones ?

(I wonder if it should be end-on or side-on to the prevailing rain winds or something... (my rain is nearly always from the West).