Author Topic: Rain gauge might not be right  (Read 9322 times)

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Offline phil2010

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Re: Rain gauge might not be right
« Reply #25 on: May 16, 2010, 01:04:20 PM »
Ok guys, I'll leave the screws alone and see how they go.

Hopefully in the next few days I'll get the wind sensor higher up on a post and move it slightly to the left. Hopefully this will make the wind direction and speed more constant and stable? Heres a pic with a red line where Im thinking of bolting the post too?

« Last Edit: May 16, 2010, 01:18:55 PM by phil2010 »

Offline stevebrtx

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Re: Rain gauge might not be right
« Reply #26 on: May 16, 2010, 05:34:02 PM »
Uh yep, I'd say about a 10' pole is in order. I've got some big Jacaranda trees to the West of the house and even though I'm on a tall pole on a 2 story house I still need about another 25' to get up into clear air, oh well, it's not like it "pays extra".

Offline 4wd

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Re: Rain gauge might not be right
« Reply #27 on: May 17, 2010, 03:04:46 AM »
It wants to be above the nearby trees etc if you can do it.
The 'official' height is 33 feet above ground, not many can do that unless putting it on an existing structure.
There isn't much wind pressure on a pole with a light anemometer on it so get it high as possible!

Offline DanS

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Re: Rain gauge might not be right
« Reply #28 on: May 17, 2010, 04:06:28 AM »
I believe in Phil2010's case the main consideration for his anemometer height is determined by he being able to handle it safely from his chair since it doesn't sound like he has others to help out. It may make things a little easier if your mast rests on the ground and attached up higher on that fence and when you need to get to the anemometer, detach  it from the fence and back up, letting it follow you down slowly. 10 or 15 feet shouldn't be too difficult to maneuver. Make sense?

Offline phil2010

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Re: Rain gauge might not be right
« Reply #29 on: May 17, 2010, 05:17:06 AM »
Well Ill get my parients todo the batt change when the time comes, but still I want to make it as easy as poss todo so.. Im thinking of mounting the post on the next post to the left of the redline, cos will be even further away from the 2 fur trees.. Im going to bolt the post on, as DanS suggested in my other thread, and then when the batts need changing, just unbolt the post and take it off. Plus I will be able to have the post as high as it will go :-) The post that im going to use is about 2meters high,, so I could have quarter to half a meter bolted to the post, then the rest sticking ubove the chicken pen/run.
« Last Edit: May 17, 2010, 05:21:04 AM by phil2010 »

Offline DanS

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Re: Rain gauge might not be right
« Reply #30 on: May 17, 2010, 06:04:17 AM »
Phil2010, I just remembered something that was suggested to another forum member that may help in your situation. Just substitute your fence for the shed wall shown here. One pulley on the top of the fence behind the mast and one near the ground with a rope through them both. Seems like it would help raising and lowering.
http://www.wxforum.net/index.php?topic=6210.msg57873#msg57873

Dan

Offline phil2010

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Re: Rain gauge might not be right
« Reply #31 on: May 26, 2010, 04:39:30 PM »
Sorry for not replying back, but I couldn't get my parents to put the wind sensor on a post higher up cos they said it wouldn't make much diff, its not that bad where it is I guess.

Anyway does this seem right, it rained this afternoon but my rain gauge hasnt tipped once,, but the rainfull in my area says 0.14inch.. look... Rainfall is the last column




« Last Edit: May 26, 2010, 04:42:36 PM by phil2010 »

Offline DanS

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Re: Rain gauge might not be right
« Reply #32 on: May 26, 2010, 07:33:12 PM »
I wouldn't use someone else's data for a comparison, especially with that low of an amount. There's a possibility your gauge received less rain where it is and not enough to tip once. You saw it tip and send data from previous rains, right?

Offline phil2010

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Re: Rain gauge might not be right
« Reply #33 on: May 26, 2010, 08:11:17 PM »
I wouldn't use someone else's data for a comparison, especially with that low of an amount. There's a possibility your gauge received less rain where it is and not enough to tip once. You saw it tip and send data from previous rains, right?

Yeah it tips fine and it has tipped twice when it rained heavy a few weeks ago(0.04inch a tip), but light ran dont make it tip even if its rained for a few hrs, Im going to get some rain x at some point too and see if that helps.
« Last Edit: May 26, 2010, 08:12:58 PM by phil2010 »

Offline sam2004gp

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Re: Rain gauge might not be right
« Reply #34 on: May 27, 2010, 06:36:21 AM »
I wouldn't use someone else's data for a comparison, especially with that low of an amount. There's a possibility your gauge received less rain where it is and not enough to tip once. You saw it tip and send data from previous rains, right?

Yeah it tips fine and it has tipped twice when it rained heavy a few weeks ago(0.04inch a tip), but light ran dont make it tip even if its rained for a few hrs, Im going to get some rain x at some point too and see if that helps.

Phil on your rain issues.  I would verify that the rain gauge is setting perfectly level.  If this is not the case, the gauge will not tip accurately, and may be some of the issues that are bothering you.  On the inside of the gauge, there may be a "X" molded into the plastic to help.  I found that just placing a small carpenter's level across the top of gauge was sufficient. 

Since your OS rain gauge is similar in design to mine. I would recommend that you do the following mod.  Since I have done mine, there have many days that I have recorded a daily rainfall that has stayed well below the normal accuracy of 1 MM (.04inches) of the gauge.  After many days of this low amount it can add up for your monthly or yearly totals.  Why even sometimes it will even record rainfall when we get a heavy laden spring fog.  If you were to do this modification, it would increase your measuring resolution to the point of about 0.25 MM.  The best part is it would cost you less then 14pounds($20 US dollars) to do it.

http://www.wxforum.net/index.php?topic=2738.0
SAM --->>> http://www.mountcrawfordweather.org
OS WMR-968 with a Dedicated PWS Weather Computer running VWS v13.01 p09


Offline tomcj2

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Re: Rain gauge might not be right
« Reply #35 on: May 27, 2010, 08:12:42 AM »
Here is a short segment from a CoCoRaHS newsletter that I just received:


_
Quote
*One gauge or two?*_

If you only have one rain gauge to check, then you're pretty sure your
gauge is always right.  But what if you have more than one gauge?  Then
you're not sure.  I have gotten in the habit of having two CoCoRaHS rain
gauges outside most of the time.  I compare rainfall from two different
places in my yard.  The readings are usually very close, but the gauge
mounted in a more protected location closer to the ground usually has
.01 or 0.02" more than the gauge that's up on top of the post.

Several CoCoRaHS volunteers keep more than one gauge.  Today, a
volunteers from near Rochester, MN discovered a large discrepancy
between his two gauges.  He has one gauge with the funnel off and one
with the funnel and inner cylinder in place.  Here is his report.  One
gauge read 2.68" (with the funnel and inner cylinder in place -- normal
operations) while the second gauge with no funnel or inner tube measured
3.04"

Station Number: MN-OL-1   Station Name: Rochester 3.9 ESE
Observation Date 5/26/2010 7:00 AM   Submitted 5/26/2010 10:37 AM
Total Precip Amount    3.04 inches
Notes   Intense Rain. duration of about 1 hour evidence of small
hail(shredded leaves)Two COCORAHS gaugues one with funnel and inner tube
one without 2 ft apart gauge with funnel recorded 2.68 inches Some tree
damage due to wind.
 
So which was right?  Most likely the wind-driven rain and hail partially
splashed and bounced out of the funnel while the gauge without a funnel
caught more of the storm and was probably the more correct of the two
readings in this situation.  At other times, the gauge with the funnel
will provide a better estimate since water evaporates more quickly when
there is no funnel in place.  It just goes to show, that even our
"accurate" gauges are sometimes only approximations.
« Last Edit: May 27, 2010, 08:14:30 AM by tomcj2 »

Davis VP2 (6163), WL 5.9.0..  VWS 14.01 p25, Panasonic HM371A camera. WU & W4U KORCANBY3, CoCoRaHS OR-CC-27

Offline phil2010

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Re: Rain gauge might not be right
« Reply #36 on: May 31, 2010, 05:51:50 PM »
This afternoon I bought some rainx and applied it to the funnel and checked to make sure its still level, so we will see if that makes a diff when it rains lightly, but it did say "do not use on plastic"??? :?. A few days ago we had a day of rain and my rain gauge reported slightly more then the "Weather Underground" of 10.6mm :grin:

Anyone know how often the rainx needs applying??
« Last Edit: May 31, 2010, 05:55:22 PM by phil2010 »

Offline phil2010

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Re: Rain gauge might not be right
« Reply #37 on: June 01, 2010, 08:40:37 AM »
Ive just checked the gauge after its been raining,, and theres still beads of rain in the funnel?? :???: :???:

Offline phil2010

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Re: Rain gauge might not be right
« Reply #38 on: June 01, 2010, 10:03:49 AM »
Ive just re applied it,, maybe I didnt wait long enough before polishing it off and it was still wet.

Offline phil2010

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Re: Rain gauge might not be right
« Reply #39 on: June 02, 2010, 05:50:15 AM »
Ive just re applied it,, maybe I didnt wait long enough before polishing it off and it was still wet.

If the rainx dont do much, I'll remove it cos you can see markings, I dont know if thats just the rainx or if its perment damage to the plastic.. Ah well the gauges are only £30, so not a biggy if Ive buggered it with rainx.

 

anything