[wxqc] Looking for help with Station - Odd shift in analysis

Chris Miller c_miller_1 at hotmail.com
Tue Feb 2 15:41:35 CST 2016


Before I forget myself, thanks for all those who have helped be try and bug this weirdness out so far.  It is appreciated.

That is how I had the station setup initially, at least pretty close.  My conversion factor was a bit of a guess at first, but I managed to get closer to the figure with some of the aviation calculators.  About the time that Ted Lum gave me a number of correction values, I ran across http://www.srh.noaa.gov/epz/?n=wxcalc_altimetersetting and used that correction to get my cellphone pressure reading, previously used to drag a correction value for it from the airport, back to my station. I can make the necessary correction to the MADIS value that Ted gave me, but it is only off by about .2 mb right now for that.    Also, I am back to using WUHU.  Hopefully, Win10 will let it run properly this time, although I expect I may have to go back to Weather Display.  It is a shame that Weather Display is not keeping my basic settings for the station communication on restart, maybe that is a trial software thing, but that is not for here.

The sudden shift in expected pressure is what is driving me bonkers, I guess, especially when all the stations are gathered together for readings.  I think, when I was using the modelling to get my pressure to spec, I ended up just entered the value to line.  This was because I thought it was due to my station being too far from the reference stations (Yes, I know, bad bad.)

Usually, the two government stations and the two CWOP stations I mentioned have good analysis, yet in winter mine shifts on average 6 mb higher than my actual reading with no changes. Basically, MADIS has flagged the station as Q rather than V lately.  So, I am presuming that something I have set is giving MADIS bum data?  

I admit the jagged data, while trying to get the station back to trim, made my standard deviation go wide a few weeks.  However, once I get it settled, my station tracks the few stations I referenced in a nice tight group, save when the storms are pushing through.   Which seems to be a lot lately.  

From: Monty Wilson 
Sent: Tuesday, 2 February, 2016 00:42
To: 'Discussion of weather data quality issues' 
Subject: Re: [wxqc] Looking for help with Station - Odd shift in analysis

I’m not sure I can add much here other that ask if you over complicating the process?  

 

You should be reporting (setting) your PEET pressure to QNH.  This is the setting used by pilots when they set their altimeters.  Using this setting, the altimeter will read airport elevation above sea level when the airplane is setting on the ground.  It is reported by airports as the “altimeter setting”.  The PEET Brothers weather station does not adjust this reading for temperature, humidity, etc.  Since you have an airport within 35 or so miles, a place to start is to set the PEET pressure to be the same as the airport.  I would pick a day when the winds are calm and the pressure is either steady or changing very slowly.

 

Think of it this way…….on a steady pressure day, if a helicopter took off from your closest airport with that airports altimeter setting and then landed in your yard, its altimeter would read your (local) elevation.

 

On your Weather Display uncheck the QFE box.  A QFE setting causes the altimeter to read zero elevation when that aircraft is sitting on the ground.  That is not what you want to report.

 

I also am using the PEET Bros (U2100) and Weather Display software.

 

Hope this helps

 

Monty Wilson, AP677/NR0A

jwilson16 at cableone.net

 

From: wxqc-bounces at lists.gladstonefamily.net [mailto:wxqc-bounces at lists.gladstonefamily.net] On Behalf Of Chris Miller
Sent: Monday, February 01, 2016 6:56 AM
To: gladstonefamily73.net at tedlum.com; Discussion of weather data quality issues
Subject: Re: [wxqc] Looking for help with Station - Odd shift in analysis

 

Calibration shifts are usually after a data loss (power outage causing battery death in the main panel) where I have to get a reading from CYYB and then use few days to trim it to what seemed right.  (storms have been running local power through the grinder here)  I wish the PEET had a better battery life then I would drag it right to the airport. 

 

Then, to find a better way to get my data back running after a power outage, I started using the barometer reading off my phone to get the initial setting and tried comparing the phone to the local pressure at CYYB, when near it, to cross check and it seemed good.  I then used the stations either side of me to test the setting by taking the reads from them and estimating the expected pressure and that seemed to hit similar values when wx was stable.  Is this not a reasonable process?

 

As far as I know the sensor in the PEET station does not send temp corrected data on the fly and it does not have an altitude setting.  Neither did WUHU.  I only started using the Altitude setting in Weather Display when I started not trusting my math for the altitude correction.  

 

Just to be sure, before I shift it back to the corrected value on the PEET station,  with an altitude of 196m (643 feet i think is correct conversion) and a sensor height of about 6 feet above that how much pressure is the correction factor?  I keep getting 23.6 mb to be added, but I am going to presume my sources are corrupt.

 

 

 

 

 

From: Ted Lum 

Sent: Sunday, 31 January, 2016 23:07

To: Chris Miller ; Discussion of weather data quality issues 

Subject: Re: [wxqc] Looking for help with Station - Odd shift in analysis

 

Actually, half of it looks like temperature variation. The other half looks like the calibration was being pushed all over the place.

http://media.tedworld.com/AU770.Month.pdf

On 1/31/2016 10:42 PM, Ted Lum wrote:

  It's not agreeing with neighbors any more than a broken clock is right twice a day. That chart is the last 180 days against the airport (CYYB) . Your variance is a full 12 mb, which is among the worst I've seen, probably since you're in Canada with a 109°F temp variation in the past 180 days.... and that's after I took out the garbage from your ill-fated calibration attempts that were over 25mb.

  Suggest you set all elevations to zero, and calibrate to Altimeter directly, at least until you can figure out where the correction is coming from.

  On 1/31/2016 8:26 PM, Chris Miller wrote:

    setting in weather display is set for qfe checked and barometer on Peet 2100 set to absolute pressure, however I have also tried setting on PEET weather station set to corrected pressure on both weather display and WUHU with same results both winters.  Right now I seem to slot in with the neighbouring stations shown in the posting so I thought I was close.   I don’t see any settings in PEET weather station that would be adding in the temperature correction, or in the software as far as i can tell, but If someone can point me toward the setting it would be appreciated.

     

    From: Ted Lum 

    Sent: Sunday, 31 January, 2016 19:51

    To: Discussion of weather data quality issues 

    Subject: Re: [wxqc] Looking for help with Station - Odd shift in analysis

     

    You appear to be sending Sea Level Pressure (SLP) in stead of Altimeter. SLP is temperature corrected, thus your error will vary with temperature which varies with season. You need to fix the settings in the software, or replace it.

    http://media.tedworld.com/AU770.pdf

    On 1/26/2016 6:19 PM, Chris Miller wrote:

      Good day to all in the group.

       

      I have a weather station, AU770, that I am trying to figure out what has happened.  During the summer, I had been getting good analysis graphs, thumbs up, and check marks for my barometer data and such after bugging out station settings and battling power loss resets.  (May be visible in the data as strong standard deviation spikes)

       

      However, once the fall weather presented itself, my analysis dropped away and the chart started showing my barometer low by 6 mb on average (humidity analysis dropped by 10 percent, but I am putting that one to issues with local humidity being higher due to nearby river influence)

      I tried switching software, in case WUHU was not doing its work properly, to Weather Display as a trial.  Things shifted to better for a while, but then returned to the same behaviour.  I then tried setting my barometer up to give the local pressure and let Weather Display do the math, in case my estimate of the local pressure translated to sea level was wrong.  I still ended up with the same number as I thought with no change in graphing or thumbs and checks even with a trial period.

       

      So, now I am wondering if the error is related to a few of the local stations having weird barometer readings?

      My nearest stations, CYYB, CYWA, and AV065, AR943 seem to track appropriately usually bracketing my graph for the most part to within a mb.  However, E2423 and E2429 usually report about 13 mb lower than the expected pressure.   So, I wonder if that is skewing my estimate graph and the thumbs and checks, not knowing which stations they are using for my local group for L3 filtering?

      I wish more of the government weather stations reported pressure, and reported it with the same consistency in the METAR data, as this would probably fix some of my skewing that I see.  I expect my local group is not very local for the L3 check and MADIS checks.

       

      I realise that it is not a big deal that the analysis graphs are off, as that is based on the lumped data with no L3 filtering of bad stations, as I understand it.  But the MADIS check is also showing bad, so I may be being removed from the data group when the data is actually good.   And since the stations are very sparse up here, I am trying to keep my station on spec as much as I can.  

      Now, if I could get in contact with the owner of E2423 and get those stations all on spec, we would have a significant gain in good pressure readings.  He has 15 stations at least, spread all over Ontario, all with pressure and location issues.  Although, I think some of that may be related to barometer offset altitude.  Regrettably, there is no way to indicate the height of the sensor relative to your surface altitude in the system, that I have noticed.

       

      If it is not that, then what is it that I have not set correctly on the station that causes this skewing of the data seasonally, or over a period since the chart cleared for a while after the software change?  

       

       

       

      Thanks in advance for any assistance,

       

      Chris

      AU770

       

     

   



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