Topic: Barometer Calibration / Clarification

[rayman]

Hi,

Sorry for asking a common question, but I'm still not really understanding the topic.  New VP2 install.  Most advice seems to be something along the lines of, find a reliable source, like the nearest airport, and calibrate your barometer to that.  I get the idea that using a reliable reference is sound advice, but I live in area that has a lot of elevation changes, and while it isn't far away, my house is over 300' higher than the nearest airport.  Wouldn't my pressure be lower?  Do I still set the barometer to match the airport, or do I perform a calculation somehow that will factor in my higher elevation and calibrate?  As it currently stands the two readings are not far off.  My airport has 1020.1 mb and my station has 1021.3 mb.  My instinct tells me to leave it as is since it was probably calibrated by Davis, but some clarification would be appreciated and I just want to understand the topic.

Thanks

[galfert]

Elevation difference between you and nearest METAR point doesn't matter. That is why you calibrate to Sea Level. That is the premise of using Sea Level Pressure so that you can compare to neighbors and the elevation does not matter.

Your Absolute pressure would be different. But you aren't comparing that.

[galfert]

There are two steps for calibrating the VP2 for barometric pressure.

1. Set your altitude which is your elevation. This include whatever ground level is plus the height of your display console. Keep this in mind if you later decide to move the console between floors as you'll need to adjust your total elevation. So the console needs this elevation which is whatever is you ground level above sea level plus the height of your console (that is where the barometer is).

2. Optionally you then correct or calibrate the Barometric Pressure which might need a minor adjustment so that you are equal to nearest METAR. You can see how to do this on page 27 of the VP2 user manual:
https://www.davisinstruments.com/product_documents/weather/manuals/07395-234_IM_06312.pdf

* Note that you will not always be at exactly the same pressure as the local METAR depending on how the barometric isobars are across the landscape. What this means is that there are better times than others to calibrate. If you are close to a METAR then this doesn't really apply. But if you are a good distance away say more than 30 or 40 miles then it can start to make a difference. Take a look at this post to understand this next level of refinement dealing with isobars:
http://www.wxforum.net/index.php?topic=36579.msg375947#msg375947

TIP: If you want to be even more precise then switch your console to use hPa and then calibrate using those units. Most METAR report in hPa also so this isn't difficult. Then when you match more closely you can then switch back the units to show inHg if you prefer that, as the calibration changes done under hPa will still be there. This is just because with the VP2 you can only adjust up or down by 0.01 inHg but you can adjust by 0.1 hPa which is more precise (because 0.1 hPa is ~ 0.003 inHg).

[rayman]

I see what you're saying, that makes sense.  Especially when to calibrate.  I should have done it the other day when the isobars were very far apart.  We're getting some wind and rain now in the mid-atlantic.  Should be a fun Halloween to watch the weather!  I had a Vantage Vue previously, which was a great little unit, but I couldn't mount it on the roof to get good wind data.  Now I'm thrilled to have the anemometer on the roof and keep the other sensors away from the hardscape.

As you can see I still have a lot to learn so any additional resources, especially good maps, would be greatly appreciated!  I was hoping to find someone on YouTube who did a learning series but nothing yet.  So far these are some of the best maps I've been able to find:

https://weather.cod.edu/analysis/ particularly,
https://climate.cod.edu/data/surface/US_zoom/contour/current/USZOOM.fronts.gif
https://www.wpc.ncep.noaa.gov/html/sfc-zoom.php
https://radar.weather.gov/Conus/full_loop.php
https://www.star.nesdis.noaa.gov/GOES/sector.php?sat=G16&sector=eus

Thanks for your help.

[jgentry]

I see what you're saying, that makes sense.  Especially when to calibrate.  I should have done it the other day when the isobars were very far apart.  We're getting some wind and rain now in the mid-atlantic.  Should be a fun Halloween to watch the weather!  I had a Vantage Vue previously, which was a great little unit, but I couldn't mount it on the roof to get good wind data.  Now I'm thrilled to have the anemometer on the roof and keep the other sensors away from the hardscape.

As you can see I still have a lot to learn so any additional resources, especially good maps, would be greatly appreciated!  I was hoping to find someone on YouTube who did a learning series but nothing yet.  So far these are some of the best maps I've been able to find:

https://weather.cod.edu/analysis/ particularly,
https://climate.cod.edu/data/surface/US_zoom/contour/current/USZOOM.fronts.gif
https://www.wpc.ncep.noaa.gov/html/sfc-zoom.php
https://radar.weather.gov/Conus/full_loop.php
https://www.star.nesdis.noaa.gov/GOES/sector.php?sat=G16&sector=eus

Thanks for your help.

If I were you, I would get a Vantage Vue Console or a WeatherLink Live “console” and use the Altimeter setting. All you would have to do is to make sure your elevation is correct, everything else is taken care of.

[klschmidt]

If attempting to calibrate a VP2 to an airport barometer, be aware that the data provided by airports is usually "altimeter" as opposed to "sea level pressure". As jgentry mentioned, a Vue console allows you to set the barometer to "altimeter", but a VP2 does not have this option. If the station you are comparing with is providing "sea level pressure", calibration on a day when the isobars are far apart should work fine. Attempting to calibrate a VP2 from a station that provides "altimeter" data does not work well because temperature is also a factor. That said, if sea level temperature has been 59 degrees for the last 12 hours, "altimeter" and "sea level pressure" should be about the same.

Sea level temperature = (Altitude*.0035) + Station Temperature, when Altitude = FT, Temperature = Fahrenheit

I think I'd assume factory calibration is correct until proven otherwise.

[galfert]

If I were you, I would get a Vantage Vue Console or a WeatherLink Live “console” and use the Altimeter setting. All you would have to do is to make sure your elevation is correct, everything else is taken care of.

The Vue console (and the WLL) have the exact same 2 steps required for proper barometric pressure calibration as the VP2 console....1. setting elevation...2. fine calibration of the barometer. I wouldn't exactly call it setting the elevation and that everything else is taken care of. The only advantage you get by not using the VP2 console is the option of using Altimeter Pressure versus Sea Level Pressure. And having Altimeter at the console is not necessarily a desired requirement by many people as many as myself prefer Sea Level Pressure as most meteorologists use this to compare different locations, whereas pilots and local media tend to report Altimeter. There is no right or wrong here...just a mater of preference. I would though say that in my case I use Sea Level Pressure for everything except that my software (Meteobridge) automatically computes Altimeter only for CWOP as that is required. So in essence I have both Altimeter and Sea Level Pressure depending on where I look at the data.

If attempting to calibrate a VP2 to an airport barometer, be aware that the data provided by airports is usually "altimeter" as opposed to "sea level pressure". As jgentry mentioned, a Vue console allows you to set the barometer to "altimeter", but a VP2 does not have this option. If the station you are comparing with is providing "sea level pressure", calibration on a day when the isobars are far apart should work fine. Attempting to calibrate a VP2 from a station that provides "altimeter" data does not work well because temperature is also a factor. That said, if sea level temperature has been 59 degrees for the last 12 hours, "altimeter" and "sea level pressure" should be about the same.

Sea level temperature = (Altitude*.0035) + Station Temperature, when Altitude = FT, Temperature = Fahrenheit

I think I'd assume factory calibration is correct until proven otherwise.

Most METAR reports I've seen show both Altimeter and Sea Level Pressure. I'm using aviationweather.gov.

[CW2274]

I wouldn't exactly call it setting the elevation and that everything else is taken care of.

But it is. You can fine tune if you desire, but it's not necessary. Merely enter the correct elevation MSL....boom, Bob's your uncle.

[galfert]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

[CW2274]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

Well, that may be the case with Ambient, but not with the Vue. Enter the correct elevation and it's done, instantly. I should know, I own two and they're spot on accurate without a fine tune.

[jgentry]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

To use the MSLP on Davis, yes you will me to calibrate it. But using the Altimeter setting on the VUE console or WLL, you do not calibrate it. It automatically calibrates itself.

[galfert]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

Well, that may be the case with Ambient, but not with the Vue. Enter the correct elevation and it's done, instantly. I should know, I own two and they're spot on accurate without a fine tune.

No, I'm not speaking about my Ambient experience. I'm speaking of my Davis experience which I've manged to help about a dozen people across the globe and I recently started managing WeatherSTEM stations (all Davis).

[galfert]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

To use the MSLP on Davis, yes you will me to calibrate it. But using the Altimeter setting on the VUE console or WLL, you do not calibrate it. It automatically calibrates itself.

Well then what is the purpose of page 28 on the Vue manual then? (where it mentions manually calibrating barometric pressure).

[CW2274]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

Well, that may be the case with Ambient, but not with the Vue. Enter the correct elevation and it's done, instantly. I should know, I own two and they're spot on accurate without a fine tune.

No, I'm not speaking about my Ambient experience. I'm speaking of my Davis experience which I've manged to help about a dozen people across the globe and I recently started managing WeatherSTEM stations (all Davis).

Good for you. Have you owned a Vue console with hands on experience? I'm telling you the way it is (at least for the altimeter), if that's not satisfactory for you...too bad. Just because the manual says set the pressure doesn't necessarily mean it's necessary. The only reason I can see screwing with it is if you don't know your exact elevation (at least within 10'), then calibration may be necessary.

[jgentry]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

Well, that may be the case with Ambient, but not with the Vue. Enter the correct elevation and it's done, instantly. I should know, I own two and they're spot on accurate without a fine tune.

No, I'm not speaking about my Ambient experience. I'm speaking of my Davis experience which I've manged to help about a dozen people across the globe and I recently started managing WeatherSTEM stations (all Davis).

That’s cool! How did you get a chance working with WeatherSTEM?  With my experience with the Davis stations, the MSLP calibrations don’t last long. I calibrated a VP2 console at a local Extension office (station belongs to Auburn University). I basically put the elevation to “0” and calibrated the Barometer to the nearest ASOS altimeter. The barometer has done well and doesn’t need frequent calibrations.

[CW2274]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

Well, that may be the case with Ambient, but not with the Vue. Enter the correct elevation and it's done, instantly. I should know, I own two and they're spot on accurate without a fine tune.

No, I'm not speaking about my Ambient experience. I'm speaking of my Davis experience which I've manged to help about a dozen people across the globe and I recently started managing WeatherSTEM stations (all Davis).

I basically put the elevation to “0” and calibrated the Barometer to the nearest ASOS altimeter. The barometer has done well and doesn’t need frequent calibrations.

Which is fine and dandy, I did this exact thing with my VP2 console until I got the Vue. The problem is if you're using it as to emulate the altimeter setting, it works quite well until you get into substantially high or low pressure.

[galfert]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

Well, that may be the case with Ambient, but not with the Vue. Enter the correct elevation and it's done, instantly. I should know, I own two and they're spot on accurate without a fine tune.

No, I'm not speaking about my Ambient experience. I'm speaking of my Davis experience which I've manged to help about a dozen people across the globe and I recently started managing WeatherSTEM stations (all Davis).

Good for you. Have you owned a Vue console with hands on experience? I'm telling you the way it is (at least for the altimeter), if that's not satisfactory for you...too bad. Just because the manual says set the pressure doesn't necessarily mean it's necessary. The only reason I can see screwing with it is if you don't know your exact elevation (at least within 10'), then calibration may be necessary.

You are right...potentially you could make all the adjustments just with elevation. The trouble is that elevation information isn't always precise enough and there is room for error there. Also although stations are factory calibrated I can see perhaps some small deviation and unless you pay for NIST calibration you just don't know. And yes I've also worked on a couple of Vue stations....but predominantly VP2.

[CW2274]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

Well, that may be the case with Ambient, but not with the Vue. Enter the correct elevation and it's done, instantly. I should know, I own two and they're spot on accurate without a fine tune.

No, I'm not speaking about my Ambient experience. I'm speaking of my Davis experience which I've manged to help about a dozen people across the globe and I recently started managing WeatherSTEM stations (all Davis).

Good for you. Have you owned a Vue console with hands on experience? I'm telling you the way it is (at least for the altimeter), if that's not satisfactory for you...too bad. Just because the manual says set the pressure doesn't necessarily mean it's necessary. The only reason I can see screwing with it is if you don't know your exact elevation (at least within 10'), then calibration may be necessary.

The trouble is that elevation information isn't always precise enough and there is room for error there.

Hence the fine tune if deemed necessary, and with proper software, down to the foot (0.001 inHg).

[galfert]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

Well, that may be the case with Ambient, but not with the Vue. Enter the correct elevation and it's done, instantly. I should know, I own two and they're spot on accurate without a fine tune.

No, I'm not speaking about my Ambient experience. I'm speaking of my Davis experience which I've manged to help about a dozen people across the globe and I recently started managing WeatherSTEM stations (all Davis).

That’s cool! How did you get a chance working with WeatherSTEM?  With my experience with the Davis stations, the MSLP calibrations don’t last long. I calibrated a VP2 console at a local Extension office (station belongs to Auburn University). I basically put the elevation to “0” and calibrated the Barometer to the nearest ASOS altimeter. The barometer has done well and doesn’t need frequent calibrations.

I got to work with WeatherSTEM by reaching out to them when they first came online with MesoWest this past August and I noticed that several stations were affecting Gladstonefamily analysis of neighbor stations because they weren't quite calibrated as well as they could be and there were some with bad humidity sensors. I reached out to them and got to meet the key players. They were very receptive in having me help out.

[jgentry]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

Well, that may be the case with Ambient, but not with the Vue. Enter the correct elevation and it's done, instantly. I should know, I own two and they're spot on accurate without a fine tune.

No, I'm not speaking about my Ambient experience. I'm speaking of my Davis experience which I've manged to help about a dozen people across the globe and I recently started managing WeatherSTEM stations (all Davis).

That’s cool! How did you get a chance working with WeatherSTEM?  With my experience with the Davis stations, the MSLP calibrations don’t last long. I calibrated a VP2 console at a local Extension office (station belongs to Auburn University). I basically put the elevation to “0” and calibrated the Barometer to the nearest ASOS altimeter. The barometer has done well and doesn’t need frequent calibrations.

I got to work with WeatherSTEM by reaching out to them when they first came online with MesoWest this past August and I noticed that several stations were affecting Gladstonefamily analysis of neighbor stations because they weren't quite calibrated as well as they could be and there were some with bad humidity sensors. I reached out to them and got to meet the key players. They were very receptive in having me help out.

That’s awesome! Off topic here... But I’m hearing good results from the newest batch of the 31 sensor that Davis uses.

[galfert]

In my experience that fine tuning can represent as much a 1 millibar (0.03 inHg).....which I think is significant enough to warrant doing something about it.

Well, that may be the case with Ambient, but not with the Vue. Enter the correct elevation and it's done, instantly. I should know, I own two and they're spot on accurate without a fine tune.

No, I'm not speaking about my Ambient experience. I'm speaking of my Davis experience which I've manged to help about a dozen people across the globe and I recently started managing WeatherSTEM stations (all Davis).

That’s cool! How did you get a chance working with WeatherSTEM?  With my experience with the Davis stations, the MSLP calibrations don’t last long. I calibrated a VP2 console at a local Extension office (station belongs to Auburn University). I basically put the elevation to “0” and calibrated the Barometer to the nearest ASOS altimeter. The barometer has done well and doesn’t need frequent calibrations.

I got to work with WeatherSTEM by reaching out to them when they first came online with MesoWest this past August and I noticed that several stations were affecting Gladstonefamily analysis of neighbor stations because they weren't quite calibrated as well as they could be and there were some with bad humidity sensors. I reached out to them and got to meet the key players. They were very receptive in having me help out.

That’s awesome! Off topic here... But I’m hearing good results from the newest batch of the 31 sensor that Davis uses.

Yes I agree. So far so good....let's hope they last.

[Liamdog4]

Galfert, what quality chart would you rely on more to set the barometer? CWOP site or Mesowest? seems if I set mine to local metar data, seems CWOP shows a negative average error but if I look at the metar data, seems just about right on. And Mesowest doesn't really tell you if your low or high. I read where CWOP Gladstone is not that reliable data. and there data drops out during the day all the time I noticed. Maybe I am just not doing something correctly? my station ID is FW6636. thank you for your input.

[galfert]

Galfert, what quality chart would you rely on more to set the barometer? CWOP site or Mesowest? seems if I set mine to local metar data, seems CWOP shows a negative average error but if I look at the metar data, seems just about right on. And Mesowest doesn't really tell you if your low or high. I read where CWOP Gladstone is not that reliable data. and there data drops out during the day all the time I noticed. Maybe I am just not doing something correctly? my station ID is FW6636. thank you for your input.

To calibrate your barometer I would recommend you use NOAA's Aviation Weather Center website. In your case you have 1 very near METAR and 4 other relatively close METAR.

https://aviationweather.gov/metar/data?ids=K22N&format=decoded&date=&hours=0

https://aviationweather.gov/metar/data?ids=KHZL&format=decoded&date=&hours=0
https://aviationweather.gov/metar/data?ids=KABE&format=decoded&date=&hours=0
https://aviationweather.gov/metar/data?ids=KXLL&format=decoded&date=&hours=0
https://aviationweather.gov/metar/data?ids=KMPO&format=decoded&date=&hours=0

Always take reading at the top of the hour to get the latest current METAR data, between 11 AM and 2PM is good, when conditions are fair and steady. If you do it at other times it is possible that the data is not current, especially during changing conditions.

I'd use K22N since it is so close to you. But it is good to compare K22N to the others nearby to make sure they agree. Since the others are a bit further away you should not dismiss any just because they differ a bit as it is likely that they differ just because of how the isobars line up at that given moment. At other times when the isobars are lined up differently then you may notice that they do match up. To learn more about isobars and this more advanced method of comparison I suggest taking a look at this post:
https://www.wxforum.net/index.php?topic=36579.0

Always ignore the Gladstonefamily analysis as it isn't worth much, especially because all that is required is for a neighbor CWOP station to send in bad data and throw the whole thing off. If you've calibrated your barometer according to local METAR and you've taken isobars into consideration, then you'll know your data is right without needing to even see what Gladstonefamily.net thinks of your data. What you can do is reach out to those neighbors that are messing up the analysis to that you can help them out. You can find out CWOP contact into if you look here:
http://www.wxqa.com/states/PA.html

Mesowest analysis is a bit more reliable and they tend to throw out bad data.
https://mesowest.utah.edu/cgi-bin/droman/regress_database_top.cgi?stn=F6636

Yes Mesowest doesn't tell you high or low but that doesn't matter much if you followed the above procedure...as you'll know. You don't need a graph. Better than a graph is to just know at any given moment if you should be the same, higher, or lower than a METAR based on isobars.

I've looked at your data and it looks to me like your barometer is properly calibrated. No adjustment necessary.

[Liamdog4]

Thank you for your input. I have been looking at K22N. Never thought about using KABE and others to compare. I didn't realize how other local bad data affects my data. I saw it mentioned here at times but I don't understand how it can affect my data being sent. I guess it has to do with average of data being sent but I would have thought  not.
I will look into the isobar link you provided. I know what they are but again, never thought of using that data. I guess that's why I am not a meteorologist! Have a good day and stay safe.

[galfert]

Well your neighbors aren't affecting your data, rather they are affecting your analysis. The analysis performed is based on the neighbor's data as it relates to your data. It is like hedging a bet or voting. The more that agree with a given data point then there is more consensus on what is deemed correct with no consideration given to anything else. One nearby bad station is all that is needed for it to become and issue of your data versus their data for the analysis results. It is a poor way to do an analysis comparison which is how Gladstonefamily.net does its thing. In theory it works well if there are more than just two nearby stations and if everyone properly maintains and calibrates their station, then the outlier can easily be identified and singled out. But the real world is that there are several poorly running stations.