Trixology

General Category => General Discussion => Topic started by: Felix on June 21, 2015, 11:55:02 AM

Title: Davis rain gauge overwhelmed last night
Post by: Felix on June 21, 2015, 11:55:02 AM: We had a major storm front pass through yesterday evening with three very intense rainfall peaks occurring at roughly one-hour intervals between 7 and 9:30 p.m. WeatherCat calculated rain/hour intensity levels exceeding 10 inches/hour for periods ranging from two to seven minutes at various times. Apparently the Davis tipping-bucket rain gauge design is unable to keep up rainfalls of that intensity because the total amount recorded was 0.22 inch lower than what was observed in the manual CoCoRaHS gauge. OTOH, a Vaisala piezoelectric rain gauge was within 0.04 inch of what was observed in the manual gauge....out of a total rainfall amount just slightly under 2? inches.
Title: Re: Davis rain gauge overwhelmed last night
Post by: Blicj11 on June 21, 2015, 03:21:35 PM: Wow. That is a major storm! Most of of us with the 4 inch CoCoRaHS manual gauge have observed that the manual gauge is slightly more accurate than the Davis tipping-bucket.
Title: Re: Davis rain gauge overwhelmed last night
Post by: Felix on June 21, 2015, 07:03:02 PM: Blick, I've noted in those previous threads that my CoCoRaHS gauge usually reads a couple hundredths more than the Davis rain gauge...a hundredth to fill up the bucket the first time and a hundredth left in the bucket when the rain stops. In this case, the point I was making was that the tipping bucket apparently just couldn't keep up with the volume of water. We're talking a lot more difference than a couple hundredths.
Title: Re: Davis rain gauge overwhelmed last night
Post by: LesCimes on June 21, 2015, 09:27:25 PM: I don't think I have ever had it rain that hard here; so haven't pushed the Davis rain gauge to its limits. I wonder if Davis Instruments has any tech info on the upper limits of the rain gauge's ability to accurately record rainfall. Ten inches in an hour is torrential! Neat that WeatherCat allows rain data to be entered manually so corrections can be made at times like this.
Title: Are you sure? (Re: Davis rain gauge overwhelmed)
Post by: elagache on June 21, 2015, 10:18:18 PM: Dear Felix, Blick, and WeatherCat station caregivers,

Quote from: Felix on June 21, 2015, 11:55:02 AM
We had a major storm front pass through yesterday evening with three very intense rainfall peaks occurring at roughly one-hour intervals between 7 and 9:30 p.m. WeatherCat calculated rain/hour intensity levels exceeding 10 inches/hour for periods ranging from two to seven minutes at various times. Apparently the Davis tipping-bucket rain gauge design is unable to keep up rainfalls of that intensity because the total amount recorded was 0.22 inch lower than what was observed in the manual CoCoRaHS gauge.

I just checked the Davis console manual and it claims that the maximum rate that a Davis VP-2 rain gauge can measure is 100" of rain an hour. Do you think you were getting that much rain?

If not, perhaps your rain gauge needs some servicing. Maybe there is some junk that is interfering with the bucket tip mechanism - spider webs maybe?

FYI . . . . . . . Edouard
Title: Re: Davis rain gauge overwhelmed last night
Post by: Felix on June 21, 2015, 10:46:50 PM: Well, based on what you found in the manual Edouard, I suppose I could have something stuck in the tipping-bucket mechanism. I'll check it tomorrow. We had periods of really hard rain but it certainly didn't come anywhere near 100 inches/hour! Thanks for the info.
Title: Re: Davis rain gauge overwhelmed last night
Post by: xairbusdriver on June 22, 2015, 02:03:20 AM: After discovering how much stuff was in my rain funnel in the first month, I've started inspecting it weekly. Last week I also discovered that the treated post had really shrunk! That made it lose enough that it could move from the vertical. I think being non-vertical can also affect the tip bucket; increased friction, or over/under filling the buckets.
Title: Re: Davis rain gauge overwhelmed last night
Post by: LesCimes on June 22, 2015, 11:30:46 PM: Quote
I've started inspecting it weekly

Good advice for all of us! 100" an hour - that is quite a threshold. Noah's flood perhaps? [thunder]
Title: Re: Davis rain gauge overwhelmed last night
Post by: Felix on June 23, 2015, 06:05:06 PM: Quote from: LesCimes on June 22, 2015, 11:30:46 PM

Good advice for all of us! 100" an hour - that is quite a threshold. Noah's flood perhaps? [thunder]

That's nearly three tips of the 0.01 inch bucket per second! If that's even possible, I'd think the accuracy would decrease significantly as the rate goes up...which may explain why I had such a large error in the three 10 inch/hour downpours. Looks like I may have to dig out the book Edouard referenced to see if it gives any accuracy guarantees at the higher rainfall rates.

BTW, pulled the collector off and took a look, no leaves nor critters were in the tipping mechanism.
Title: Re: Davis rain gauge overwhelmed last night
Post by: xairbusdriver on June 23, 2015, 08:38:30 PM: Quote
pulled the collector off and took a look, no leaves nor critters were in the tipping mechanism.
Do you have the upside down plastic cone/screen thingy? I'm not sure they've always had that. I see they have a different one that's more like a slotted disk, I think he cone-shaped one has smaller slots and traps stuff better, but I've not run any scientific tests...
(http://i1327.photobucket.com/albums/u666/xAirbusDriver/Part-7345.530-2_zpsbccp2gan.gif)
Part #: 7345.530, $8.00
Title: Davis backs off - a bit. (Re: Davis rain gauge overwhelmed)
Post by: elagache on June 24, 2015, 12:15:27 AM: Dear Felix, X-Air, and WeatherCat Davis station owners,

Quote from: Felix on June 23, 2015, 06:05:06 PM
Looks like I may have to dig out the book Edouard referenced to see if it gives any accuracy guarantees at the higher rainfall rates.

In my almost 6 year old copy of the Davis console manual, you'll find the number on page 49.

Looking at the current manual which is available online:

http://www.davisnet.com/product_documents/weather/manuals/07395-234_IM_06312.pdf (http://www.davisnet.com/product_documents/weather/manuals/07395-234_IM_06312.pdf)

You'll find the specifications on page 52 instead. Also, they have backed off the peak rate just a bit - to quote:

Quote
Rain rate: to 96''/hr.; 2438 mm/hr

Quote from: xairbusdriver on June 23, 2015, 08:38:30 PM
Do you have the upside down plastic cone/screen thingy? I'm not sure they've always had that. I see they have a different one that's more like a slotted disk, I think he cone-shaped one has smaller slots and traps stuff better, but I've not run any scientific tests...

Most of us have this simpler design (photo from Scaled Instruments:)

(https://www.scaledinstruments.com/wp-content/uploads/2014/02/7342.0311.jpg) (https://www.scaledinstruments.com/product/davis-7342-031-debris-screen-for-rain-collector-cone/)

Scaled Instruments does have the upgraded debris screen available for those who want it:

https://www.scaledinstruments.com/product/davis-7345-530-pro2-bird-spikedebris-screen-kit/ (https://www.scaledinstruments.com/product/davis-7345-530-pro2-bird-spikedebris-screen-kit/)

Cheers, Edouard [cheers1]
Title: Re: Davis rain gauge overwhelmed last night
Post by: Felix on June 24, 2015, 12:45:02 AM: Found this link, Edouard and they make no accuracy guarantee above a rainfall rate of four inches/hour.

http://www.davisnet.com/product_documents/weather/manuals/07395-275_IM_07852.pdf

And my collector screen is the same as yours.
Title: Re: Davis rain gauge overwhelmed last night
Post by: xairbusdriver on June 24, 2015, 01:25:00 AM: Highly recommend the new and improved model. You might ask for "upgrade pricing" and a loyalty discount! I'm bettin' you can arrange a "deal" for less than $50! :o
Title: Odd, isn't it! (Re: Davis rain gauge overwhelmed last night)
Post by: elagache on June 24, 2015, 11:23:21 PM: Dear Felix, X-Air, and

Quote from: Felix on June 24, 2015, 12:45:02 AM
Found this link, Edouard and they make no accuracy guarantee above a rainfall rate of four inches/hour.

Hmm, interesting! The same document gives the same absolute limits. Sure looks to me like Davis is trying to have it both ways.

What sort of rainfall rates was your station reporting at the time? Were you significantly above 4"/hr?

Quote from: xairbusdriver on June 24, 2015, 01:25:00 AM
Highly recommend the new and improved model. You might ask for "upgrade pricing" and a loyalty discount! I'm bettin' you can arrange a "deal" for less than $50! :o

It does look nice. However, my rain gauge has relatively few things getting into it because it is on a second story with not much in the way of trees nearby. However, if I have to buy some other part for my station, I'll probably buy it then. I do like the improved collector cone design, but that would prevent me putting a cap on the rain gauge during the summer. Having a cap on it seems to solve most of my bird problems since they have nothing to land on.

Cheers, Edouard [cheers1]
Title: Re: Davis rain gauge overwhelmed last night
Post by: xairbusdriver on June 25, 2015, 02:23:21 AM: Actually, the cone/top is well below the top/rim of the gauge. Whatever you were using for a cap should still work. I assume that you do not use/have the anti-bird "spikes" either. The newer collector has ting holes in the top of the little bump thingies around the rim of the collector. You are "given" a straight piece (about six inches long) of stainless (I hope) wire to stick into each hole. Supposedly helps prevent a bird for using the collector as a perch. Wouldn't mind them sitting there if they were facing the center of the collector, but facing outward buts the south end of a north facing bird over the collector. Not the end we enjoy learning about! [blush] Of course, even the other end could have some seed parts that they would drop into the collector. Apparently, having "Davis" plastered on two sides of the collector was not enough to discourage these aviators... [banghead] [rolleyes2]
Title: Re: Davis rain gauge overwhelmed last night
Post by: Bull Winkus on June 25, 2015, 04:25:11 AM: I always thought it was just the bird's way of letting me know that those little round beachball (to them) seeds were not their favorite. Since I switched to the more expensive variety, their makeshift loo has not backed up. ? Of course, the spikes help too.

(http://www.davisnet.com/news/enews/images/2009-03birdonvane.jpg)

Not my station or image. [lol]
Title: Re: Odd, isn't it! (Re: Davis rain gauge overwhelmed last night)
Post by: Felix on June 25, 2015, 10:48:42 AM: Quote from: elagache on June 24, 2015, 11:23:21 PM

What sort of rainfall rates was your station reporting at the time? Were you significantly above 4"/hr?

Believe my first post said in excess of 10 inches/hour, three separate times. And those weren't just momentary peaks at that intensity!

Hence, why I said the gauge was "overwhelmed." Quite frankly, I just flat don't believe a tipping bucket design emptying at three times/sec (for a 100 inch/hour rate) could maintain a reasonable accuracy level...which is likely the reason Davis is silent about accuracy beyond the four inch/hour rate.
Title: Re: Davis rain gauge overwhelmed last night
Post by: xairbusdriver on June 25, 2015, 02:04:46 PM: I tend to agree with you, Felix. Sounds like some user testing with measured amounts of water are called for! I think the very small hole probably allows some water to be 'stored' in the collector for some time and provide a more constant, but slower tipping process. That would help the total measurement, but could limit the accuracy of any 'rate' info. Frankly, I've looked askance at the "Rain Alerts" that ended up having only hundredth of an inch total accumulation. "Raining buckets at a time?" Probably not. Of course, it's the total (daily, weekly, etc.) that are the most important. A 'professional' instrument might have separate systems for rates and totals. Maybe Bull could train that bird to 'announce' various rates; it might as well be trained to do something rather than prevent accurate wind info!! [banghead]

BTY, I'm pretty sure that 'bird spike' is an 'after-market' item! :)
Title: Explanation and gauge cap (Was: Davis rain gauge overwhelmed last night)
Post by: elagache on June 26, 2015, 12:26:18 AM: Dear X-Air, Felix, Herb, and WeatherCat station caregivers,

Quote from: Felix on June 25, 2015, 10:48:42 AM
Believe my first post said in excess of 10 inches/hour, three separate times. And those weren't just momentary peaks at that intensity!

Hence, why I said the gauge was "overwhelmed." Quite frankly, I just flat don't believe a tipping bucket design emptying at three times/sec (for a 100 inch/hour rate) could maintain a reasonable accuracy level...which is likely the reason Davis is silent about accuracy beyond the four inch/hour rate.

I guess you have your explanation. Although 10 inches of rain an hour means the buckets are tipping once every 3 seconds or so. That doesn't sound beyond what the rain gauge could handle. Perhaps the problem is at that rate a lot of the water spills around the buckets.

I wonder if there is any station on the market that can cope with rainfall rates like that? There is one maker who is considered even more rugged than Davis, but I've forgotten the name.

Quote from: xairbusdriver on June 25, 2015, 02:23:21 AM
Actually, the cone/top is well below the top/rim of the gauge. Whatever you were using for a cap should still work.

Yes, that's correct. However, it doesn't seem like enough of an improvement to just buy that considering the shipping. I'll wait until I need some other Davis parts.

Quote from: xairbusdriver on June 25, 2015, 02:23:21 AM
I assume that you do not use/have the anti-bird "spikes" either. The newer collector has ting holes in the top of the little bump thingies around the rim of the collector.

I don't think I could change to the newer collector cone because of the projections for anti-bird spikes. Here is a photo of my cap before applying the paint:

(http://canebas.smugmug.com/Nature/Weather/Red-Vines-to-rain-gauge-cap/i-FZfCF6d/0/XL/Test%20fitting%20cut%20cap%20%28annotated%29-XL.jpg)

It really fits very snugly around the existing cone, so it wouldn't work with the new cone. Here is what it looks like after painting:

(http://canebas.smugmug.com/Nature/Weather/Red-Vines-to-rain-gauge-cap/i-vRv8sBV/0/XL/IMG_2420-XL.jpg)

Simple, but keeps the dust out during the long dry season . . . . . (http://www.canebas.org/WeatherCat/Forum_support_documents/Custom_emoticons/desert-smiley.gif)

Cheers, Edouard [cheers1]
Title: Re: Davis rain gauge overwhelmed last night
Post by: Blicj11 on June 26, 2015, 02:19:50 AM: Quote from: xairbusdriver on June 25, 2015, 02:04:46 PM
Frankly, I've looked askance at the "Rain Alerts" that ended up having only hundredth of an inch total accumulation.

Depends on where you live. Here in the west we live for a hundredth of an inch. That's definitely a rain day.
Title: Re: Davis rain gauge overwhelmed last night
Post by: xairbusdriver on June 26, 2015, 02:29:05 AM: You're correct, you couldn't easily put a cap/cover on the new collector and have the spikes in place. OTOH, they aren't installed when the collector ships; they are too easily bent. They could also be removed anytime you want, of course, being only a friction fit, but you would eventually wear out/enlarge the holes. The birds might appreciate that, however, so they could use the wires as tools to dig out insects/grubs behind some bark...

While I do get a small commission on on each new collector sale, I agree that it's not worth a special order. That commission barely pays the rent now, and I've already got a job lined up for my wife, so we're fine with your waiting a while to by. ;D

Quote
keeps the dust out during the long dry season
I suppose you get a week or so warning before any rain?! :o [banghead] [lol]
Title: Re: Davis rain gauge overwhelmed last night
Post by: Bull Winkus on June 26, 2015, 08:26:39 AM: I actually made my spike hat out of square hole wire cloth mesh.

(http://www.birdbarrier.com/mmBBASTORE/Images/N8-SS50_wire-cloth-mesh_lrg.jpg)

I used a garment tape to measure the circumference of the rain collector, then cut a strip to fashion as a hat with the ends wired together. Then snip, snip with the side cutters until the whole thing looked very uninviting to land on for even the toughest of feathered dinosaurs.

[spin]
Title: Re: Davis rain gauge overwhelmed last night
Post by: xairbusdriver on June 26, 2015, 03:30:30 PM: "GARMENT TAPE"!!! Wait until the duct tape police hear about this!!!!

I used some of that "cloth" to block the holes for the attic exhaust fans. No problem with birds, but the regular, nylon screening was no challenge for the raccoons! ;)

And now, back to the regularly scheduled "overwhelmed" topic...

Just a noobie question: Wouldn't the wire cloth break up the regular rain into smaller 'drops'? If so, would that affect the 'rain drop' counter?! [goofy]
Title: Re: Davis rain gauge overwhelmed last night
Post by: Blicj11 on June 26, 2015, 03:38:15 PM: Herb, once again you have maintained your place on my Hero List.
Title: Re: Davis rain gauge overwhelmed last night
Post by: Felix on June 26, 2015, 06:15:20 PM: We had another intense thunderstorm last night...0.84 inches in 28 minutes including one five-minute period when the rate was calculated to be 5.59 inches/hour.

The Davis rain gauge had no problem keeping up with that intensity level...as is almost always my experience, it registered 0.02 inches less than the nearby CoCoRaHS manual gauge.
Title: Read forecast - VERY - carefully! (Was: Davis rain gauge overwhelmed)
Post by: elagache on June 26, 2015, 09:31:55 PM: Dear X-Air, Blick, Herb, Felix, and WeatherCat rain gauge architects,

Quote from: xairbusdriver on June 26, 2015, 02:29:05 AM
Quote
keeps the dust out during the long dry season
I suppose you get a week or so warning before any rain?! :o [banghead] [lol]

Quote from: Blicj11 on June 26, 2015, 02:19:50 AM
Quote from: xairbusdriver on June 25, 2015, 02:04:46 PM
Frankly, I've looked askance at the "Rain Alerts" that ended up having only hundredth of an inch total accumulation.

Depends on where you live. Here in the west we live for a hundredth of an inch. That's definitely a rain day.

As Blick points out, when you live in a drought, you take a very different stance on precipitation. Lots of us put the automotive product Rain-X on our rain gauges:

https://www.rainx.com/product/glass-water-repellents-cleaners/rainx-original-glass-treatment/ (https://www.rainx.com/product/glass-water-repellents-cleaners/rainx-original-glass-treatment/)

When you are in misty conditions, this reduces the water tension and gets more drops into the rain gauge. That's how desperate we are out here in the west.

As to how to cope with a cap on the rain gauge, it is really quite easy. I read the National Weather Service local forecast discussion that are normally updated twice a day. If there is any chance for rain anywhere nearby - I take the cap off. When the chance passes by, the cap goes back on. Even last winter, the conditions were so dry that the cap was on the gauge for a sizable fraction of winter. During the summer, it is rare indeed that the cap is removed.

As Jimmy Durante would say: . . . . . "Such are da' conditions that prevail!"

Oh well, Edouard
Title: Re: Davis rain gauge overwhelmed last night
Post by: Bull Winkus on June 27, 2015, 05:15:20 AM: Quote
Just a noobie question: Wouldn't the wire cloth break up the regular rain into smaller 'drops'? If so, would that affect the 'rain drop' counter?! [goofy]

Perhaps my description was a little too vague. I don't have a picture of it. I cut a length (or strip) of the material long enough to wrap around the top, overlapping the edge on the outside. It was held in place by friction and the ends fastened together by bending the wire. The part left sticking above the edge of the rain cup was cut up with side cutters, leaving jagged, pointy antennas signaling to the birds, "Don't land here!"
[lol] [lol] [lol]

Quote
Herb, once again you have maintained your place on my Hero List.

THANKS Blick! ? I consider that very high praise coming from you. You have my utmost respect and admiration!
[rockon] [rockon] [rockon]