Topic: WH40 rain gauge funnel extension

[slybarman]

Supposed to rain 1-2" tomorrow. I don't have manual gauge yet, best I'll be able to do is a few close-by stations on weather underground.

[wxperson]

For info, this is what you get for the funnel extension. Obvious use of the bird spike strip to go through the holes. I may look at using a large hose clamp instead.

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What did you end up using?   Seems like a hose clamp without the spike kit might work OK.

[Rover1822]

I used the bird spike kit as opposed to a hose clamp. The metal band from the kit slides through slots in the extension that are too small for a hose clamp.

[Rover1822]

OK, first results, inconclusive, as although I had about 0.65" (inches) of rain, both Wh40s are within a percentage point on reporting , as they always have been.

Now, to be fair, the rain was not heavy, just lengthy in duration.

So, have to keep waiting for a "heavy" rain event , more common in spring/summer here as opposed to fall/ winter as it is now, where this might mitigate the capture and bounce effect

[wxperson]

Regarding this gauge and extension.

My observations so far indicate the gauge is very accurate with light or moderate rain... but with heavy rain it underestimates the rainfall... compared to a Cocorahs gauge.

Hopefully the higher edge will help with heavy rain but I wonder if part of the problem is the small increment for each tip.... and that the tipping cannot "keep up" with heavy rain.

Each tip is .004".   Let's do some math.

Say you have a thunderstorm with rain rates of 6"/hour.   Not unusual in Florida and here in Georgia.  I have seen it as high as 14"/hour in short burst... But let's stick with 6"/hour.

That rate equates to .10" per minute... which is 25 tips per minute or one every 2.4 seconds.   That's a lot of tips.  If you ever poured water into the funnel you notice that you may only get a few tips because the tipping spoon stays in the down position as water flows in.   

If we take it to the next level... say 8"/hour... we are up to 33 tips per minute... less than 2 seconds.

We won't even talk about 10+/hour which does occur in short burst. 🤪

Anyhow... I am not making any definitive statements but just throwing the idea out there.

We may not see very heavy rains around here until Spring and Summer but for now... I will be trying out the extension and testing it out.   

Thanks for listening

George

[Rover1822]

You do know this subject has been beat to death on other threads, and may have been the input for getting the extension , right?

when the WH40 first came out there was tons of discussion on this thread.
https://www.wxforum.net/index.php?topic=39166.0

So this current thread is relevant to those trying an extension

Sorry, if this came off rude, a larger number of us are looking for an answer, for a problem, you seem to agree with.
This was not meant to be insulting, but for those of us with the unit (or multiple units) , we are very familiar with the issues, and yours fall in line. Now, if you get the extension, we would love your results

[wxperson]

Not insulted... I will check out the other thread.

I did install it today.

[kheller2]

There is a mixture of sleet, rain, flurries around me right now so nothing is accurate for me to report on.  However, I did notice something odd that my WH40 and WH65 sensors are reporting very little precipitation today.  In fact, all the Ambient/Ecowitt units around my area are showing next to nothing precipitation wise, yet a few acurite stations are reporting  -- and matching my Status.  Very weird.  I wonder if the units are frozen.

[slybarman]

I think my WH-40 is still under-reporting with the extension. Yesterday I recorded 2.58" of rain and the two stations closest to me recorded 2.69 and 2.71. Precip rate maxed out at .6"/hr.  I still had a correction factor of 1.1 entered in my console.

I ordered a manual rain gauge today that I will try to use for calibration. The two other stations are pretty close by, but that is not to say they got the exact same rainfall as I did.

[Rover1822]

Actually that is not bad , your are within 5% of the other stations. I believe the % error for the WH40 is like +/- 5%

Also, I don't expect to see a benefit to the extension until one experiences a heavy rain, forceful, something well over a rate of 1 inch hour.

[slybarman]

5% but WITH the 1.1 correction factor, so really . . . ??%

[Rover1822]

Yeah, forgot that.
Well, you will get a better idea when you get the manual gauge in. I can vary quite a bit from one end of the property to the other.

We recommend the "Stratus" rain gauge, a bit pricey , but works very well

[slybarman]

I have another 2+ inches of rain coming tomorrow and I have my manual gauge to compare against.

For the sake of this next comparison, should I reset the offset on the WH40 to zero or leave at 1.1?

Will starting at zero, make it easier to figure out a proper offset later?

[Gyvate]

if you measure in imperial units, I would leave it at 1.0 to begin with.

[slybarman]

About half way through our rain event and so far my WH40 seems to be tracking fairly well. Manual gauge is just over .9 and WH40 = .86. This is with the offset back to 1.0. The rain rate was never too heavy. I'll compare it again tomorrow.

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[slybarman]

Final number this morning WH40 = 1.22  Manual gauge 1.32.  Is this worth compensating for with an offset? If so, what number (1.08?)?

My rainfall rate never got high enough for the funnel extension to matter, but I feel like I at least have a good baseline now for future measurements and it is one more data point with regard to the WH40's overall accuracy.

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[giusCB]

Final number this morning WH40 = 1.22  Manual gauge 1.32.  Is this worth compensating for with an offset? If so, what number (1.08?)?

My rainfall rate never got high enough for the funnel extension to matter, but I feel like I at least have a good baseline now for future measurements and it is one more data point with regard to the WH40's overall accuracy.

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your manual gauge is too small ...

[Rover1822]

My values from yesterday, all gauges cleaned just before rainfall.

WH40 , no extension   0.65 inch
WH40 , with extension 0.71 inch
Manual Stratus            0.68 inch

Subjective observation , at one point during the event , rain changed characteristics and consisted of large raindrops for a short period. Until then, the WH40s were identical in values, after that the WH40 with the extension pulled ahead. I checked afterwards for any signs of debris, and there was none.

[WXDA]

My values from yesterday, all gauges cleaned just before rainfall.

WH40 , no extension   0.65 inch
WH40 , with extension 0.71 inch
Manual Stratus            0.68 inch

Subjective observation , at one point during the event , rain changed characteristics and consisted of large raindrops for a short period. Until then, the WH40s were identical in values, after that the WH40 with the extension pulled ahead. I checked afterwards for any signs of debris, and there was none.

Do you have any gain applied to the WH40s?

[Rover1822]

No,  gain is default 1.00

[slybarman]

Would you consider the WH40 as having over-reported then with the funnel?

[Rover1822]

This was only one event, and I'm not going to quibble about 0.03" difference compared to the manual.
Need more events for anything conclusive

[Ra1nman]

Surely Ecowitt just need to bite the bullet and either design a taller funnel which can be retrofitted, or, if the problem is also related to the tipping mechanism, go all in with a new gauge. Extending in this way is better than not but it compromises the bird spikes and isn't the most ideal solution. Having a more 'professional' rain gauge would be nice for enthusiasts, Ecowitt of course need to factor in cost

[Rover1822]

No argument. But I am glad they are making a cheap ($) effort to address the issue for existing owners of the WH40.

Note that not everyone has the same rain experiences at their location.

But as I have said before, distribution of a new funnel would have been preferred. Something that didn't have what I call the 2 stage funnel angles. If the lower angle had been extended to the full diameter of the metered area, and maybe add a higher lip, there never would have been this issue that we have been talking about for years. Specifically, in some heavy rain circumstances , the drop may , in essence, splatter, discarding part of its content outside the funnel.

For some of us, this type of heavy rain event , especially in the summer, is quite frequent.

It also makes it harder to determine if the extension works , at least for me at this time of year, as those types of rain events are less frequent.

[Rover1822]

I'm going to add a little more fun to this.

The WH40 data I posted, was fairly tight in values (fairly). Now I also have results from my WS90, and my WH65 , although they are not co-located , they are within 80 feet of my WH40s and my manual.  So here is the full list

WH40 , no extension   0.65 inch
WH40 , with extension 0.71 inch
Manual Stratus            0.68 inch
WH65                         0.79 inch (known to report high)
WS90                         1.02 inch (this unit has always read high, it might just be my specific unit)

All units , not calibrated.
I have, and continue to regard the WH40 as the best option for a rain gauge for this product line.