Author Topic: Under-reporting or over-reporting?  (Read 3342 times)

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Offline ggsteve

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Under-reporting or over-reporting?
« on: August 22, 2016, 10:34:07 AM »
We had a nice soaking rain pass through overnight with about an inch of much needed rain for most of Mass.  My Cocorahs gauge reported .99" this morning, while the Rainwise right next to it reported 1.05".  These two gauges are usually within .01" of each other after a rain.  6% is a pretty big difference.  Who do you think is over or under reporting?
Rainwise Mk III w/wind extension, Oracle Multi & IP-100  West Townsend, MA
Wunderground: https://www.wunderground.com/personal-weather-station/dashboard?ID=KMATOWNS8#history
https://rainwise.net/weather/steve01474
http://www.pwsweather.com/obs/MORSE1.html
http://www.awekas.at/en/instrument.php?id=12597
CWOP: http://www.findu.com/cgi-bin/wxpage.cgi?call=EW7173
CoCoRaHS: MA-MD-47
Skywarn Spotter ID: 16-266
Bloomsky Sky2

Davis Vantage Pro2 w/WL Fitchburg H.S., Fitchburg, MA
Wunderground: https://www.wunderground.com/personal-weather-station/dashboard?ID=KMAFITCH5#history
CoCoRaHS: MA-WR-52

Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #1 on: August 22, 2016, 11:33:37 AM »
We had a nice soaking rain pass through overnight with about an inch of much needed rain for most of Mass.  My Cocorahs gauge reported .99" this morning, while the Rainwise right next to it reported 1.05".  These two gauges are usually within .01" of each other after a rain.  6% is a pretty big difference.  Who do you think is over or under reporting?

If my gauges were only 6% different, I would tear down the goal posts in celebration! For example, in a single rain storm last week my VP2 recorded .32, Mr. CoCo had .39, and Mr. Rainwise had .36. All three collectors were reasonably close together. However, based on nearby reliable PWSs, I believe Mr. CoCo is probably the most accurate. Wind and gusts probably contributed to the differences in my recorded amounts. I used to "lose sleep" over such differences, but now I accept the differences as long as they are "directionally correct" (in my case, the three readings meet that description) and let it go at that. If the readings were .32, vs .67 vs. 1.40, that would be reason to be concerned because clearly something is wrong. What is a bit frustrating is both my VP2 and Rainwise "tippers" were made in 2016. But it goes to show you that the old fashion rain gauge, Mr. CoCo, is the tried and true reliable tool. No mechanisms or parts to go awry, just a plain and simple gauge (costing about $30) made from plastic!
« Last Edit: August 23, 2016, 07:49:45 AM by WheatonRon »
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline nincehelser

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Re: Under-reporting or over-reporting?
« Reply #2 on: August 22, 2016, 02:45:35 PM »
I'd put my money on the CoCoRaHS gauge.  It has no mechanics mess up.


Offline CW2274

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Re: Under-reporting or over-reporting?
« Reply #3 on: August 22, 2016, 03:53:15 PM »
I'd put my money on the CoCoRaHS gauge.  It has no mechanics mess up.
Exactly. I have both and use the Coco as my "official" reading, but the RW is good.
Davis Wireless VP2 SHT31 24hr 67CFM FARS
RW Tipper w/ CoCoRaHS

Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #4 on: August 24, 2016, 08:31:05 PM »
We had a nice soaking rain pass through overnight with about an inch of much needed rain for most of Mass.  My Cocorahs gauge reported .99" this morning, while the Rainwise right next to it reported 1.05".  These two gauges are usually within .01" of each other after a rain.  6% is a pretty big difference.  Who do you think is over or under reporting?

If my gauges were only 6% different, I would tear down the goal posts in celebration! For example, in a single rain storm last week my VP2 recorded .32, Mr. CoCo had .39, and Mr. Rainwise had .36. All three collectors were reasonably close together. However, based on nearby reliable PWSs, I believe Mr. CoCo is probably the most accurate. Wind and gusts probably contributed to the differences in my recorded amounts. I used to "lose sleep" over such differences, but now I accept the differences as long as they are "directionally correct" (in my case, the three readings meet that description) and let it go at that. If the readings were .32, vs .67 vs. 1.40, that would be reason to be concerned because clearly something is wrong. What is a bit frustrating is both my VP2 and Rainwise "tippers" were made in 2016. But it goes to show you that the old fashion rain gauge, Mr. CoCo, is the tried and true reliable tool. No mechanisms or parts to go awry, just a plain and simple gauge (costing about $30) made from plastic!

   Now I have done it! I have added more confusion to life. As noted above, I have three tools that have provided me rainfall measurements—a new VP2 ISS, a Rainwise 111 gauge and Mr. CoCo. To help determine the accuracy winner, I decided I would add a fourth tool—my 11 year old VP2 that I have upgraded with a new tipper mechanism (Davis part number 7852.804 Vantage Pro2 Rain Bucket Base and Bucket), SHT 31 and a thoroughly cleaned ISS (it sat in a bleach solution for 24 hours and it looks almost new)! Since I have two VP2 consoles, I can capture the VP2 ISS data (the new one and the refurbished one) separately—with a little help from Davis support (the console directions are horrible for doing this task, Davis walked me through the changes in less than 1 minute!)  Unfortunately, I took two steps forward and three back. We had a modest rainfall today and the measurements follow: the new VP2--.25; the refurbished VP2--.34; the Rainwise--.29; and Mr. CoCo--.32. Each are reasonably close in proximity to each other at similar height above ground. Oh well, I am enjoying life with this hobby. Time will tell and additional rainfalls will be necessary, but I think the refurbished VP2 and Mr. CoCo are the apparent winners--at least today! I felt comfortable going to my new VP2 ISS (that uploads data to CWOP and WU) and manually "tipping" the rain bucket 9 times so CWOP and Weather Underground received what I believe are the "best" rainfall amounts.

Another winner are folks that own Davis equipment. The Davis telephone support is great, unfortunately the online support (e-mail) is slow to respond--but waiting on the phone for a few minutes and talking with a USA based support person is pretty unique and special. It makes you appreciate the Davis equipment and its higher cost. Brett Lane is the person in charge of Davis support--kudos to him and his team!
« Last Edit: August 25, 2016, 09:59:17 AM by WheatonRon »
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline ggsteve

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Re: Under-reporting or over-reporting?
« Reply #5 on: September 19, 2016, 06:45:46 AM »
Goldilocks syndrome this morning.  Rainwise on the roof: 1.30" (too low), Rainwise next to Cocorahs 1.44" (too high), Cocorahs gauge 1.36" (just right!).

Regardless of which was correct, it was a pleasure to hear a nice, soaking rain on the roof this morning.  It was hard to get up!
Rainwise Mk III w/wind extension, Oracle Multi & IP-100  West Townsend, MA
Wunderground: https://www.wunderground.com/personal-weather-station/dashboard?ID=KMATOWNS8#history
https://rainwise.net/weather/steve01474
http://www.pwsweather.com/obs/MORSE1.html
http://www.awekas.at/en/instrument.php?id=12597
CWOP: http://www.findu.com/cgi-bin/wxpage.cgi?call=EW7173
CoCoRaHS: MA-MD-47
Skywarn Spotter ID: 16-266
Bloomsky Sky2

Davis Vantage Pro2 w/WL Fitchburg H.S., Fitchburg, MA
Wunderground: https://www.wunderground.com/personal-weather-station/dashboard?ID=KMAFITCH5#history
CoCoRaHS: MA-WR-52

Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #6 on: September 19, 2016, 08:48:33 AM »
Goldilocks syndrome this morning.  Rainwise on the roof: 1.30" (too low), Rainwise next to Cocorahs 1.44" (too high), Cocorahs gauge 1.36" (just right!).

Regardless of which was correct, it was a pleasure to hear a nice, soaking rain on the roof this morning.  It was hard to get up!

What about your VP2 or do you attach your Rainwise to the VP2?
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline ggsteve

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Re: Under-reporting or over-reporting?
« Reply #7 on: September 19, 2016, 09:57:34 AM »
What about your VP2 or do you attach your Rainwise to the VP2?

The VP2 is at my High School about 6 miles from home and at a much higher elevation, so it is often quite different.  Today the High School reports .96" since yesterday.
Rainwise Mk III w/wind extension, Oracle Multi & IP-100  West Townsend, MA
Wunderground: https://www.wunderground.com/personal-weather-station/dashboard?ID=KMATOWNS8#history
https://rainwise.net/weather/steve01474
http://www.pwsweather.com/obs/MORSE1.html
http://www.awekas.at/en/instrument.php?id=12597
CWOP: http://www.findu.com/cgi-bin/wxpage.cgi?call=EW7173
CoCoRaHS: MA-MD-47
Skywarn Spotter ID: 16-266
Bloomsky Sky2

Davis Vantage Pro2 w/WL Fitchburg H.S., Fitchburg, MA
Wunderground: https://www.wunderground.com/personal-weather-station/dashboard?ID=KMAFITCH5#history
CoCoRaHS: MA-WR-52

Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #8 on: September 19, 2016, 10:06:35 AM »
What about your VP2 or do you attach your Rainwise to the VP2?

The VP2 is at my High School about 6 miles from home and at a much higher elevation, so it is often quite different.  Today the High School reports .96" since yesterday.

Ok. Periodically, my VP2s have been flaky when reporting rain and someone in this Forum suggested that I replace the VP2 rain gauge mechanism with the Rainwise 111. I haven't done that yet as I would prefer to fix the VP2s (I now have two).

Unrelated to this issue,  CWOP and Findu were down for over 8 hours today. Any thoughts on what happened?
« Last Edit: September 19, 2016, 05:32:09 PM by WheatonRon »
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #9 on: September 21, 2016, 10:07:53 PM »
What about your VP2 or do you attach your Rainwise to the VP2?

The VP2 is at my High School about 6 miles from home and at a much higher elevation, so it is often quite different.  Today the High School reports .96" since yesterday.

Ok. Periodically, my VP2s have been flaky when reporting rain and someone in this Forum suggested that I replace the VP2 rain gauge mechanism with the Rainwise 111. I haven't done that yet as I would prefer to fix the VP2s (I now have two).

Today's rainfall measurements--VP2 station A--.34; VP2 station B--.32; and Mr. CoCo--.55! I guess I need to recalibrate the Davis products as there was no wind and a steady but not hard rain. What a hassle!
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline ggsteve

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Re: Under-reporting or over-reporting?
« Reply #10 on: September 22, 2016, 06:33:08 AM »

Ok. Periodically, my VP2s have been flaky when reporting rain and someone in this Forum suggested that I replace the VP2 rain gauge mechanism with the Rainwise 111. I haven't done that yet as I would prefer to fix the VP2s (I now have two).

Not to be a Rainwise wonk, but I do wonder if the 8" diameter of the Rainwise increases it's accuracy.  Also, they invented the electronic tipping rain gauge, so they have had extra time to try and perfect it.  The only time I have seen my Rainwise gauges act "flaky" is when debris, especially spiders get in there.
« Last Edit: September 22, 2016, 06:34:49 AM by ggsteve »
Rainwise Mk III w/wind extension, Oracle Multi & IP-100  West Townsend, MA
Wunderground: https://www.wunderground.com/personal-weather-station/dashboard?ID=KMATOWNS8#history
https://rainwise.net/weather/steve01474
http://www.pwsweather.com/obs/MORSE1.html
http://www.awekas.at/en/instrument.php?id=12597
CWOP: http://www.findu.com/cgi-bin/wxpage.cgi?call=EW7173
CoCoRaHS: MA-MD-47
Skywarn Spotter ID: 16-266
Bloomsky Sky2

Davis Vantage Pro2 w/WL Fitchburg H.S., Fitchburg, MA
Wunderground: https://www.wunderground.com/personal-weather-station/dashboard?ID=KMAFITCH5#history
CoCoRaHS: MA-WR-52

Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #11 on: September 22, 2016, 07:38:16 AM »

Ok. Periodically, my VP2s have been flaky when reporting rain and someone in this Forum suggested that I replace the VP2 rain gauge mechanism with the Rainwise 111. I haven't done that yet as I would prefer to fix the VP2s (I now have two).

Not to be a Rainwise wonk, but I do wonder if the 8" diameter of the Rainwise increases it's accuracy.  Also, they invented the electronic tipping rain gauge, so they have had extra time to try and perfect it.  The only time I have seen my Rainwise gauges act "flaky" is when debris, especially spiders get in there.

Several others in this Forum swear by the accuracy of the Rainwise, mainly due to the larger collector base. These folks also believe if Davis went to the 8" base, the arrival of the much hoped for, VP3, would arrive.
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline ValentineWeather

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Re: Under-reporting or over-reporting?
« Reply #12 on: September 22, 2016, 08:14:14 AM »
The coco suffers from splash out on heavy rains 1-3% is common vs my NWS deep funneled 8". A small redesign to make funnel depth deeper would fix this.
Randy, the Aviator is my father in 1963 with his Indian bike

Offline miraculon

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Re: Under-reporting or over-reporting?
« Reply #13 on: September 22, 2016, 08:57:22 AM »
This article from Nolan Doesken concludes that the 4" gauge reads slightly more rain.

http://www.cocorahs.org/media/docs/AMS_NJD_GaugeComparison_AppldClimate_2-2.pdf

It doesn't explain why this might be the case. A lot of the differences in measurements, were 0.01". Could the larger funnel area hold onto more drops that didn't make it down into the gauge? Also, the SRG uses a dip stick rather than the see-through measurement tube of the CoCoRaHS gauge. Water displacement, absorption into the stick being factors?

On page 127 of Burt's Weather Observer Handbook there is a paragraph about "design, construction and materials" of the raingauge. He discusses shallow funnels, shapes and wetting characteristics of the gauge. The Burt reference seems to support the splash-out of the shallower funnel being the case.

I am not sure what to make of all this....  :-k

Greg H.










Blitzortung Stations 668, 706 - CWOP CW4114 -  CoCoRaHS MI-PI-1

Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #14 on: September 22, 2016, 09:04:01 AM »
This article from Nolan Doesken concludes that the 4" gauge reads slightly more rain.

http://www.cocorahs.org/media/docs/AMS_NJD_GaugeComparison_AppldClimate_2-2.pdf

It doesn't explain why this might be the case. A lot of the differences in measurements, were 0.01". Could the larger funnel area hold onto more drops that didn't make it down into the gauge? Also, the SRG uses a dip stick rather than the see-through measurement tube of the CoCoRaHS gauge. Water displacement, absorption into the stick being factors?

On page 127 of Burt's Weather Observer Handbook there is a paragraph about "design, construction and materials" of the raingauge. He discusses shallow funnels, shapes and wetting characteristics of the gauge. The Burt reference seems to support the splash-out of the shallower funnel being the case.

I am not sure what to make of all this....  :-k

Greg H.
A very informative article, but what exactly is "NWS Standard Rain Gauge (SRG)"? Is that similar to the Rainwise 111?
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline floodcaster

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Re: Under-reporting or over-reporting?
« Reply #15 on: September 22, 2016, 09:08:27 AM »

Quote
A very informative article, but what exactly is "NWS Standard Rain Gauge (SRG)"? Is that similar to the Rainwise 111?


See this link
Bill


Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #16 on: September 22, 2016, 09:21:02 AM »

Quote
A very informative article, but what exactly is "NWS Standard Rain Gauge (SRG)"? Is that similar to the Rainwise 111?


See this link

Wow! That gauge is really ugly! No wonder smaller designs, notably Mr. CoCo, have been developed, otherwise spouses would put an end to such "toys"!
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline floodcaster

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Re: Under-reporting or over-reporting?
« Reply #17 on: September 22, 2016, 11:11:14 AM »

Quote
A very informative article, but what exactly is "NWS Standard Rain Gauge (SRG)"? Is that similar to the Rainwise 111?


See this link

Wow! That gauge is really ugly! No wonder smaller designs, notably Mr. CoCo, have been developed, otherwise spouses would put an end to such "toys"!
:-)
It has to be of sufficient capacity to capture those record events. Holds around 20 inches. Also, the larger 8-inch opening affords a better catch, especially with regards to snowfall (inside tube and funnel are removed for winter like CoCoRaHS).
Bill


Offline miraculon

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Re: Under-reporting or over-reporting?
« Reply #18 on: September 22, 2016, 11:37:40 AM »
This is NovaLynx's version of the SRG. I think that NovaLynx is better looking.
http://novalynx.com/store/pc/260-2510-Standard-Rain-Gauge-8p234.htm
ValentineWeather has one.

I saw one of the official versions at the local COOP observer, and some at the KAPX Open House. It is big.
I keep thinking about adding one to my Excessive Collection of Weather Stuff....

Greg H.




Blitzortung Stations 668, 706 - CWOP CW4114 -  CoCoRaHS MI-PI-1

Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #19 on: September 22, 2016, 11:47:28 AM »
This is NovaLynx's version of the SRG. I think that NovaLynx is better looking.
http://novalynx.com/store/pc/260-2510-Standard-Rain-Gauge-8p234.htm
ValentineWeather has one.

I saw one of the official versions at the local COOP observer, and some at the KAPX Open House. It is big.
I keep thinking about adding one to my Excessive Collection of Weather Stuff....

Greg H.

Do you have a wife that supports you in this hobby? The reason I ask, I was on the phone with Davis support awhile back talking about rain measurements and the variations I was having among the four gauges I have--2 VP2, Rainwise and Mr. CoCo. My wife asked me if Davis thought I was crazy having four gauges. I told her that having four gauges isn't all that unusual but she disagrees!
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline ValentineWeather

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Re: Under-reporting or over-reporting?
« Reply #20 on: September 22, 2016, 01:29:29 PM »
Yes that's it. I've been doing test with open COCO vs closed vs 8" and reporting back to Cocorahs.
Randy, the Aviator is my father in 1963 with his Indian bike

Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #21 on: September 22, 2016, 02:00:02 PM »
Yes that's it. I've been doing test with open COCO vs closed vs 8" and reporting back to Cocorahs.

What have you advised our friends at CoCoRaHS about the differences, if any?
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline ValentineWeather

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Re: Under-reporting or over-reporting?
« Reply #22 on: September 22, 2016, 08:45:28 PM »
The biggest difference was around 3%.
Randy, the Aviator is my father in 1963 with his Indian bike

Offline WheatonRon

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Re: Under-reporting or over-reporting?
« Reply #23 on: September 22, 2016, 08:51:36 PM »
The biggest difference was around 3%.

I would call that statistically insignificant and then tear down the goal posts in celebration!
« Last Edit: September 22, 2016, 09:21:35 PM by WheatonRon »
Davis VP2 with Daytime FARS, SHT31 (2 complete systems-1 for uploading to the internet, the other system for test and play); Rainwise 111; CWOP--CW5020; WU--KILWHEAT17; CoCoRaHS--IL-DP-132

Offline Scalphunter

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Re: Under-reporting or over-reporting?
« Reply #24 on: October 10, 2016, 12:40:41 PM »
Weird how in cultures one thinks about what spouses think about hobbies etc. Nice to have a spouse who doesn't complain about what I do. Guess it in the gents make up of native versus white.

John