Author Topic: A lot of dewpoint errors with Vantage Vue  (Read 1444 times)

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Offline kf6gtx

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A lot of dewpoint errors with Vantage Vue
« on: November 19, 2017, 04:55:08 PM »
This is my first post to the forum!

I'm uploading data to CWOP (Vantage Vue) and whenever it's a cool drippy day, I'm getting reports of streaks of Dewpoint errors.
For instance, temperature reads 44, dewpoint reports 32 with an error of +8.
On the same day, the humidity high reading was 84%, even though it was drippy all day.

What can I check on the unit to see if there's a way to fix humidity/dewpoint errors?

You can view CWOP info at http://weather.gladstonefamily.net/site/AT925
Also just starting to set up a Meteotemplate-based site at https://angw.in

Dave Bell
kf6gtx

Offline Faceng Ret

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Re: A lot of dewpoint errors with Vantage Vue
« Reply #1 on: November 19, 2017, 07:33:18 PM »
My advice at the present time is to not chase CWOP dewpoint ratings. I checked several of the stations around you and they all show dewpoint errors and they all show very strange "Worst standard deviation" numbers. The same thing has been happening for my station and surrounding stations here in Florida. My conclusion is that CWOP is broken. I have two stations collecting nearly identical readings and I am fairly sure that I am not off by their analysis of anywhere from 15 to 50 degrees.

Offline azchrisf

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Re: A lot of dewpoint errors with Vantage Vue
« Reply #2 on: November 21, 2017, 12:09:34 PM »
I'm going to mirror what Faceng said.
I fought with those damn dewpoint errors until I was ready to tear my hair out. My Station (F1398) is properly sited, and it still borders on the edge of being a red x, even though my dewpoint numbers are accurate and a station 2 and 3 blocks from me mirror nearly the same.

What I found in my case, is that there is a long running station about a mile from me that CWOP seems to like to base it's "analysis" graph off of, and which follows PERFECTLY, but his station is on a roof eve, which isn't the best place. So the data is skewed...It also doesn't take into account there can be major differences in as little as a half mile, hills and valleys, etc. etc. etc.

So, don't worry about it. How he is performing the analysis and determines what is good and bad is unknown since it's not documented.
As long as your MADIS rating is above 90%, your good. Even near perfect stations I've seen get their data flagged occasionally here and there by MADIS. Forget the Gladstone analysis, I don't think he's done work on it in a long time either.

I think it can also be summed up as it's a helpful tool, but it's not "law". I'm assuming in all this your station is sited correctly and not next to any heat sources that can throw the readings off.
« Last Edit: November 21, 2017, 12:18:22 PM by azchrisf »
Davis Vantage Pro 2 Plus 6163 w/ 8 Transmitters!
Also doing Soil and Leaf 4x
WU: KAZGLEND106 CWOP: FW1398 (F1398) Purpleair: 98793/LAZGLEND8
My setup:
https://www.wxforum.net/index.php?topic=41867.0

Offline dalecoy

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Re: A lot of dewpoint errors with Vantage Vue
« Reply #3 on: November 21, 2017, 02:23:13 PM »

For instance, temperature reads 44, dewpoint reports 32 with an error of +8.
On the same day, the humidity high reading was 84%, even though it was drippy all day.

What can I check on the unit to see if there's a way to fix humidity/dewpoint errors?


Disregarding (for the moment) CWOP .....  I suggest that you find out whether your station is measuring the dew point/humidity properly.  To do that, you'll have to borrow (or purchase) another measuring device, and measure the humidity (several different hours) at the same location as your station.  It's very important to do that very near your station.  And don't expect exact agreement - just close.

Note: Amazon has psychrometers available for less than $30.00

If your station is measuring correctly, then ignore CWOP.  Otherwise, ask here.  In any case, please let us know the results.

Offline kf6gtx

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Re: A lot of dewpoint errors with Vantage Vue
« Reply #4 on: November 21, 2017, 08:05:19 PM »
Thanks for the replies. I think it's well sited (nowhere is perfect with an all-in-one unit). It's on a pole about 7ft above the roofline on my single-story house, well away from any vents.
I'll get another device to measure humidity...and not get too uptight about it all.

Offline dalecoy

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Re: A lot of dewpoint errors with Vantage Vue
« Reply #5 on: November 21, 2017, 09:15:38 PM »
Thanks for the replies. I think it's well sited (nowhere is perfect with an all-in-one unit). It's on a pole about 7ft above the roofline on my single-story house, well away from any vents.
I'll get another device to measure humidity...and not get too uptight about it all.

If you have a "school" contact, you can probably borrow a psychrometer.

And, in my view, a personal weather station should be reporting the measurements that are correct for the place where it's located.  Not some "ideal location".  And yes, with an all-in-one unit that is often a compromise.  But it is your PWS at your location.