Author Topic: PWS Weather displays wrong barometric pressure value  (Read 5377 times)

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Offline Plug Nickel

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PWS Weather displays wrong barometric pressure value
« on: June 15, 2020, 02:30:44 PM »
Running into a strange problem.
I'm updating PWS weather with Virtual Weather Stations built in WeatherForYou / HamWeather updater.

My Virtual Weather Station software reports my barometric pressure as 30.08 and is reporting that value however PWS Weather shows it as 29.44.

Even stranger, WeatherForYou shows it correct as 30.08.

I thought WeatherForYou got its data from PWS Weather so how can they be different?

I've been sending emails to PWS Weather, but does anyone here have a clue?

Offline galfert

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Re: PWS Weather displays wrong barometric pressure value
« Reply #1 on: June 15, 2020, 03:26:21 PM »
WeatherForYou only gets data from your station if you gave them permission to use and give credit to your station for its data. Otherwise you could be seeing some other data source in WeatherForYou. When you pull up WeatherForYou do you see your station mentioned?

If you posted some of your station IDs it might be helpful for others to take a look.

Notice red arrow indicating where the data is coming from. This would be the station name in PWSweather if it is being credited.
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Offline galfert

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Re: PWS Weather displays wrong barometric pressure value
« Reply #2 on: June 15, 2020, 03:28:54 PM »
What I'm saying is that just because you upload to Hamweather (now PWSweather) doesn't mean that it automatically gets credited or used at WeatherForYou. You have to send an email to WeatherForYou and allow them to credit your PWSweather station.
« Last Edit: June 15, 2020, 03:36:04 PM by galfert »
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Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #3 on: June 15, 2020, 03:32:11 PM »

Offline galfert

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Re: PWS Weather displays wrong barometric pressure value
« Reply #4 on: June 15, 2020, 03:54:14 PM »
Looks good as in your station is being referenced and credited for the data. I think this is a question for WeatherForYou. That is strange.

Maybe WeatherForYou does not use barometric pressure from your station and they only use temperature? Or maybe they aren't using your barometric pressure because they detected a variance that was too great for your data? These are all questions for WeatherForYou.
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Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #5 on: June 15, 2020, 04:43:06 PM »
They claim they use the PWS's barometer.

From an email from them:

"We have different stations that send station pressure, altimeter, or mean sea level pressure. Our system will attempt to determine what version your station is sending based on the software.  That said, currently, the PWSweather.com website displays the Mean sea level pressure."

Offline weatherforyou

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Re: PWS Weather displays wrong barometric pressure value
« Reply #6 on: June 16, 2020, 03:37:00 PM »
WeatherForYou uses the raw data sent by your station's software, device or service.  PWSweather has begun doing further processing to calculate and standardize the readings (based on sea level, I believe).  I know the PWSweather.com developers are still working out some of the bugs in the conversions.

While WeatherForYou does get the data through PWSweather.com I take the raw data sent by your station as long as I've been requested to use that.  If a request isn't made I'll still use data from PWSweather.com but it will include any calculated change that system makes.
Joe Torsitano


Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #7 on: June 16, 2020, 03:48:19 PM »
Barometric pressure measurements always confuse me.
The data that I'm sending both PWS and WFY is adjusted for elevation above sea level.

I know that PWS is using MSLP.

How do they differ?
 

Offline galfert

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Re: PWS Weather displays wrong barometric pressure value
« Reply #8 on: June 16, 2020, 04:35:32 PM »
I think this may warrant looking at your VWS software configuration and also learning a bit more about your hardware.

What hardware is your station? What logger are you using? (I miss the that about the old PWSweather where it gave you information about the hardware used by the station).

I've never used VWS but I've glanced at the manual. It says that VWS will calculate Sea-Level Barometric Pressure. Hmmm...that is a clue right there. This means it is important for your software to have the correct elevation. It is also important to know more about your hardware. That is why I asked what is it? This might tell us what your station is passing to VWS. As it could be passing an already corrected pressure or it may be an uncorrected station pressure (QFE). I would also like to know if you have changed any of the setting in VWS in its calibration settings (Gain and Offset dialog settings). Hopefully the VWS Calibration setting is set to Gain 1.00 and Offset 0.00. I prefer to make these corrections at the console and never do these at the software level.

What I'm thinking is that you may be doing some barometric offset in VWS that you see on your software but it is not being passed to PWSweather.

Here is another issue that I see. This warrants looking into because I see that your VWS pressure along with what you see at PWSweather as being too low of a pressure to be accurate. I don't think your station is properly calibrated is what I'm saying. I'm looking at KBDU and KLMO and you are too low compared to them. Don't mention elevation differences (that is not an issue). I know people like to throw out elevation differences between them and the airport but that is not an issue.
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Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #9 on: June 16, 2020, 06:14:37 PM »
My station is a Davis Vantage Pro2 and it's got the correct elevation of 7300' entered (hence my low pressure reading).

Today my pressure is 29.72".

I have no offsets entered into anything since there is no official reporting station near me at my altitude for fine calibration.

VWS was getting pretty old, so I downloaded Weather Display software and the problem still exists.

It's reporting the corrected value to VWS as well as Weather Display and I Wire Sharked the packet it's sending and it's also sending the same elevation corrected value.


There's something going on with PWS Weather that's not occurring with WeatherForYou.

Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #10 on: June 16, 2020, 06:20:59 PM »
Forgot to say the My station is 2000' higher than the KBDU Boulder Airport.

Offline galfert

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Re: PWS Weather displays wrong barometric pressure value
« Reply #11 on: June 16, 2020, 06:53:24 PM »
My station is a Davis Vantage Pro2 and it's got the correct elevation of 7300' entered (hence my low pressure reading).
Your high elevation is not a reason for low pressure if you have properly calibrated for sea-level pressure equivalence.  Sure I would expect a low pressure for your location at your high elevation if you were reporting your QFE (station pressure also called Absolute pressure)...but nobody does that. We are only concerned with Sea Level pressure which is a number we reach because of your elevation adjustment.

Your 7300 feet almost matches what I see using FreeMapTools of 7329 feet.
https://www.freemaptools.com/elevation-finder.htm

That is enough to make 0.03 inHg difference. But I'm seeing a greater discrepancy than that...So being off by 29 feet is not the issue. It is just a small factor. There is something else going on.

Quote
Today my pressure is 29.72".
Today your pressure is 29.72 where? As in where did you pull that number from? Your VWS software, your Davis VP2 display? or Somewhere else? Because according to PWSweather you max for today only reached 29.56 at around 1:55AM (your time).

Quote
I have no offsets entered into anything since there is no official reporting station near me at my altitude for fine calibration.
Offsets or no offsets has nothing to do with stations near you at your altitude or not. I say this because I don't believe in any offsets in software. My recommendation is to make all those corrections and calibrations at the console which is the VP2 display console in your case.

Quote
VWS was getting pretty old, so I downloaded Weather Display software and the problem still exists.
I only see that you have uploaded to PWSweather. It would be helpful to see what happens when you upload elsewhere. I would recommend uploading to Weather Underground as a comparison. Helps to see if a site is manipulating your data or not.

I'm curious to hear you take a reading from 3 places at the same time and report what you see...
VP2 display console pressure reading:
PWSweather pressure: (mention which software uploaded; VWS or Weather-Display)
WeatherForYou pressure:
Weather Underground pressure: (yeah I threw this in as 4th comparison that would help, and mention which software uploaded).

Quote
It's reporting the corrected value to VWS as well as Weather Display and I Wire Sharked the packet it's sending and it's also sending the same elevation corrected value.

There's something going on with PWS Weather that's not occurring with WeatherForYou.
It would be interesting to see if VWS uploading to PWSweather is different than Weather-Display uploading to PWSweather. I think you mentioned you tried this and it didn't make a difference. But I'm not clear now from reading what you wrote if that is what you are saying. Just trying to see if the issue with PWSweather is there with both software. But it would be important to know how each software is getting the data. Meaning how is VWS getting data? Via USB logger? And when you configured Weather-Display did you then also use the same USB logger or is it pulling data from some other means?

I'm also wondering what firmware your console and logger are running?

And lastly ...just to be sure in VWS Calibration you have Barometer Gain and Offset set to 1.00 and 0.00 respectively?
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« Last Edit: June 16, 2020, 06:55:23 PM by galfert »
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Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #12 on: June 16, 2020, 07:29:19 PM »
Quote
Your high elevation is not a reason for low pressure if you have properly calibrated for sea-level pressure equivalence.  Sure I would expect a low pressure for your location at your high elevation if you were reporting your QFE (station pressure also called Absolute pressure)...but nobody does that. We are only concerned with Sea Level pressure which is a number we reach because of your elevation adjustment.

Your 7300 feet almost matches what I see using FreeMapTools of 7329 feet.
https://www.freemaptools.com/elevation-finder.htm

That is enough to make 0.03 inHg difference. But I'm seeing a greater discrepancy than that...So being off by 29 feet is not the issue. It is just a small factor. There is something else going on.

Currently, KBDU pressure is 29.76" mine as reported by my weather station, Weather Display, and WeatherFor You is 29.71" for a difference of 0.05".

I think that that difference is reasonable since I've never fine tweaked it.

We had a high (edited, mistakenly said low) pressure ridge settle in to Colorado the last few days but it's now moved out.

However, getting back to the point, PWS Weather is currently reporting 29.0".

Quote
Today your pressure is 29.72 where? As in where did you pull that number from? Your VWS software, your Davis VP2 display? or Somewhere else? Because according to PWSweather you max for today only reached 29.56 at around 1:55AM (your time).

As reported by my weather station (Vantage Pro2), Weather Display, and WeatherForYou.
Again, PWSweather is the problem.

Quote
I only see that you have uploaded to PWSweather.

Other than WeatherForYou, I'm not uploading anywhere else.
I used Weather Underground for many years until...well, you know.

I'm not using VWS now, but I checked and all the gains were 1 and all the offsets were 0.
Weather Display that I'm currently using also has no offset (it doesn't have a gain control).


« Last Edit: June 16, 2020, 08:50:09 PM by Plug Nickel »

Offline galfert

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Re: PWS Weather displays wrong barometric pressure value
« Reply #13 on: June 16, 2020, 11:03:26 PM »
As a test create a new PWSweather station ID. Don't delete your current one. You can have more than one station ID. Then start uploading to the new station ID as a test. See if that makes a difference. You only need to do this momentarily to test. Then you can switch back your software to upload to your current PWSweather ID.

I know a lot of people have given up on WU and I understand that. But if you could just upload to WU as a test to see if it a different site treats you data the same or differently we might learn something.  Or since you now are using Weather-Display you could upload to WeatherCloud also as a test.

« Last Edit: June 16, 2020, 11:05:49 PM by galfert »
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Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #14 on: June 17, 2020, 11:07:42 AM »
I temporarily created a WU account and WU agreed with everything except PWS Weather.
Gonna have to email them again.

Offline galfert

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Re: PWS Weather displays wrong barometric pressure value
« Reply #15 on: June 17, 2020, 11:14:43 AM »
What about a second PWSweather station ID to test if somehow that original ID has been messed with?
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Offline WSWeather

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Re: PWS Weather displays wrong barometric pressure value
« Reply #16 on: June 17, 2020, 03:00:10 PM »
I doubt there is anything wrong on his end.

My PWS hardware console currently shows 30.09 inches Hg which is also what the WU shows.  My PWSWeather console shows 30.04.  It is always lower by about that much.  The upload is done to each separately by Cumulus.  PWS Weather is changing the pressure figure before display.  That 0.05 inches Hg does not correspond to the difference between sea level and 655 feet AGL (my elevation), which would be closer to 0.5. However, I am already sending them the correct value.

Offline weatherforyou

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Re: PWS Weather displays wrong barometric pressure value
« Reply #17 on: June 17, 2020, 03:02:44 PM »
If you'd submit a support request with this info it may be helpful to the developers.

I doubt there is anything wrong on his end.

My PWS hardware console currently shows 30.09 inches Hg which is also what the WU shows.  My PWSWeather console shows 30.04.  It is always lower by about that much.  The upload is done to each separately by Cumulus.  PWS Weather is changing the pressure figure before display.  That 0.05 inches Hg does not correspond to the difference between sea level and 655 feet AGL (my elevation), which would be closer to 0.5. However, I am already sending them the correct value.
Joe Torsitano


Offline WSWeather

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Re: PWS Weather displays wrong barometric pressure value
« Reply #18 on: June 17, 2020, 03:07:15 PM »
Will do.   Thanks.  It wasn't enough of a difference to really worry about but in the context of this thread it is at least another data point for them to work with.

Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #19 on: June 17, 2020, 03:14:57 PM »
I sent them the following:

Currently as I type this, my PWS PlugNickel is reporting a barometric reading of 29.1".

KBDU Boulder Municipal Airport at 2000' lower in elevation than my station is reporting 29.85".

My station on WeatherForYou is reporting 29.78".

My Vantage Pro2 as well as my software "Weather Display" is also reporting 29.78".

So, my weather station and WeatherForYou is pretty accurate for the elevation difference (I'm at 7299' elevation) as compared with KBDU Boulder Municipal Airport however PWS Weather is way off.

Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #20 on: June 17, 2020, 03:17:19 PM »
Quote
What about a second PWSweather station ID to test if somehow that original ID has been messed with?

I tried but after an hour, my new station didn't show up.
Gave up because I don't want to have my "real" station not being updated.

Offline galfert

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Re: PWS Weather displays wrong barometric pressure value
« Reply #21 on: June 17, 2020, 04:20:10 PM »
After looking at this further it seems pretty convincing that PWSweather is messing with [some] station's barometric pressure uploads.

I found your neighbor running an Ambient WS-2902 that is uploading to both WU and to PWSweather. That station's barometric pressure also does not match with both services.

Neighbor on WU:  29.52 inHg
https://www.wunderground.com/dashboard/pws/KCOJAMES23

Same neighbor on PWSweather: 28.87 inHg
https://pwsweather.com/station/pws/kcojames23

For whatever reason PWSweather is messing with people's data. Interestingly though when you pass it along from PWSweather over to WeatherForYou it is the original data as uploaded.

This neighbor is experiencing the same amount of difference as the OP between their WU and PWSweather uploads of about 0.64 to 0.65 inHg. That is about 22 hPa of difference and is equivalent to messing with a station's elevation to about 616 feet!  This should not be occurring. PWSweather needs to give us some answers. If this is an oversight I hope that they take notice and fix it.


« Last Edit: June 17, 2020, 04:29:35 PM by galfert »
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Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #22 on: June 17, 2020, 05:02:38 PM »
Thanks galfert for noticing that.
I never look at their PWS since they never calibrated their barometer for elevation properly.
But yes, it's screwed up the same way.

Offline Plug Nickel

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Re: PWS Weather displays wrong barometric pressure value
« Reply #23 on: June 17, 2020, 06:30:02 PM »
Well, got an email from PWS Weather.
They said that they do have a problem in the software.
They said that since different stations send station pressure, altimeter, or mean sea level pressure, their software tries to determine what's being sent and then correct it to mean sea level pressure.

Unfortunately, when receiving mean sea level pressure as in most cases including mine, it thinks that it's getting altimeter pressure and correcting for that.

They said the problem should be corrected next week.

Thanks for the help everyone.

Offline galfert

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Re: PWS Weather displays wrong barometric pressure value
« Reply #24 on: June 17, 2020, 07:19:03 PM »
Great job getting to the bottom of the mystery. I'm glad they provided this answer.

I think it is very thoughtful that they are attempting to fix stations that send them the wrong data. Just seems like they need to tweak it to work better and not mess with good data.

This is probably only something that is an issue or noticeable at greater elevations such as yours as the calculations for Altimeter and Sea Level pressure will yield much different results.

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