Author Topic: WU: relative pressure shown instead of absolute, how can I fix that pls?  (Read 944 times)

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Offline openvista

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #25 on: February 17, 2019, 10:19:58 AM »
Randy, I have no idea why Mesowest assigns the wrong SLP readings to your stations. Like CW2274 said, I've never seen this before. My station is always very close to Mesowest's computed value. So are others I've looked at in the past.

I just looked around on a map (https://www.wrh.noaa.gov/map/?&zoom=7&scroll_zoom=true&center=46.50,-89.40&basemap=OpenStreetMap&boundaries=true,true&obs=true&obs_type=weather&elements=temp,wind,gust&obs_popup=false&obs_density=2) and couldn't duplicate the glitch with other nearby stations. Take, for instance, DW1631. It's by Sioux Falls. It was the closest I could find that sent an accurate altimeter. The SLP calculation (1014.4 mb) is fine. Just for reference, there's presently a 1014mb isobar running right through the SE border of South Dakota.  See attached pic.

Just to be clear, the Mesowest SLP formula uses the current temp, not the 12 hour avg temp. For the most part, unless there's a huge swing in temps during the day, both methods are usually within half a millibar (0.02") of each other.
« Last Edit: February 17, 2019, 10:30:11 AM by openvista »
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Offline openvista

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #26 on: February 17, 2019, 10:26:40 AM »
In terms of the original question of this thread, yes, WU seems to be unclear about what they expect. I no longer send to WU, but as of last year I was sending altimeter and they didn't mess with it. But I've also sent them SLP previous to that and they just passed it on unaltered. I have heard the complaints of others saying their altimeter was being re-calculated. So your mileage may vary.
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Offline Ronny St.

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #27 on: February 17, 2019, 10:50:05 AM »
Just a typical newbie question, though  :oops: Is there somewhere a list where to find all the abbreviations used here? Would make it easy for newbies like me to watch and learn  8-)

Online ValentineWeather

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #28 on: February 17, 2019, 10:52:32 AM »
openvista, Thanks for the explanation, it's better this morning only .03" off. Both VP2 consoles 30.17 vs Mesowest 30.20. But WOW! the airport is much lower.
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Offline galfert

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #29 on: February 17, 2019, 11:13:14 AM »
Just a typical newbie question, though  :oops: Is there somewhere a list where to find all the abbreviations used here? Would make it easy for newbies like me to watch and learn  8-)

List the abbreveations you need clarification with. Let me know if I missed any.

SLP  = Sea Level Pressure
MSLP = Mean Sea Level Pressure (an average of SLP over given time frame)
Altimeter = Another way of correcting barometric pressure for elevation that does not involve temperature changes (it assumes standard temperature of 59F)
NWS = National Weather Service
ASOS = Automated Surface Observing System - basically the NWS managed weather stations at airports mostly locally funded.
AWOS = Automated Weather Observing System - FAA managed weather stations, and federally funded. similar to ASOS. Most people interchangeably refer to METAR data and it could be ASOS or AWOS....and for the most part it doesn't matter.
CWOP = Citizens Weather Observer Program = a network of weather stations run by weather hobbyist and includes tie in to NWS NOAA MADIS system for data analysis and quality control.
WU = Weather Underground online weather website
PWS = Personal Weather Station - just a generic term for the hardware/software that an individual has for measuring and reporting weather data
METAR = Meteorological Aerodrome Report - a format of weather data reported by mostly local airports. The METAR is usually used as a reference to your local trusted weather data source.
Mesowest - a weather network run by the University of Utah. It brings in weather data from CWOP MADIS reporting stations, NWS stations, and a few other weather networks like RAWS, SNOTEL
MADIS - Meteorological Assimilation Data Ingest System - a system run by NWS NOAA that processes weather data from different sources and runs quality controls on this data. MADIS data is then distributed to be used by numerous systems.

* these definitions are close enough to being correct. Good enough for a newbie without getting too deep.
« Last Edit: February 17, 2019, 11:57:12 AM by galfert »
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Offline openvista

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #30 on: February 17, 2019, 11:14:16 AM »
openvista, Thanks for the explanation, it's better this morning only .03" off. Both VP2 consoles 30.17 vs Mesowest 30.20. But WOW! the airport is much lower.

Hmmm... the airport looks correct to me based on that map in my last post which uses ~9AM CST reports. KVTN reported 1018.5mb at 8:52AM. The surface map showed a 1018mb (30.06") contour nearby your location.  Instead, your SLP was reported as 1022.3mb (30.19") at 8:55AM. That's a pretty big error.

I see your elevation is correct. Station pressure and altimeter look correct too. I haven't the foggiest why Mesowest is churning out an SLP value that's ~4mb too high. It almost seems like they are double reducing your station pressure to sea level.
« Last Edit: February 17, 2019, 11:20:28 AM by openvista »
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Offline openvista

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #31 on: February 17, 2019, 11:22:16 AM »
I'm using these links which take the Mesowest data and present the SLP in millibars (more precise & better matched to weather maps):

https://www.wrh.noaa.gov/mesowest/timeseries.php?sid=E3958&num=72&banner=gmap&raw=0&w=325 (Randy's station)
https://www.wrh.noaa.gov/mesowest/timeseries.php?sid=KVTN&num=72&banner=gmap&raw=0&w=325 (nearby airport)
« Last Edit: February 17, 2019, 11:35:49 AM by openvista »
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Online ValentineWeather

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #32 on: February 17, 2019, 11:43:07 AM »
Nice, in Mb though.  :lol:
Randy

Offline Ronny St.

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #33 on: February 17, 2019, 11:43:33 AM »
Heh, thank you a lot, Galfert, for the effort of making that list! That explains a lot to me! Now I can try to follow the discussion knowing what the abbreviations stand for  8-)

Online ValentineWeather

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #34 on: February 17, 2019, 11:45:29 AM »
openvista, Thanks for the explanation, it's better this morning only .03" off. Both VP2 consoles 30.17 vs Mesowest 30.20. But WOW! the airport is much lower.

Hmmm... the airport looks correct to me based on that map in my last post which uses ~9AM CST reports. KVTN reported 1018.5mb at 8:52AM. The surface map showed a 1018mb (30.06") contour nearby your location.  Instead, your SLP was reported as 1022.3mb (30.19") at 8:55AM. That's a pretty big error.

I see your elevation is correct. Station pressure and altimeter look correct too. I haven't the foggiest why Mesowest is churning out an SLP value that's ~4mb too high. It almost seems like they are double reducing your station pressure to sea level.

That's why I was wondering about the accuracy. Were they doing the full calculation etc.?
« Last Edit: February 17, 2019, 11:52:05 AM by ValentineWeather »
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Offline openvista

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #35 on: February 17, 2019, 12:09:05 PM »
That's why I was wondering the accuracy. Were they doing the full calculation etc.?

It's gotta be a glitch on their end since you are sending the correct data via CWOP. I just took a look at the raw data: http://www.findu.com/cgi-bin/raw.cgi?call=EW3958. The only thing you don't send every 5 minutes is elevation, but it's listed correctly on all the links shared in this thread so far. So that's in the database somewhere with your station ID. Given all that, I don't see why Mesowest can't compute SLP properly.

If it bothers you, maybe send an email to: atmos-mesowest@lists.utah.edu. 
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Online ValentineWeather

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #36 on: February 17, 2019, 12:23:00 PM »
Thanks...I use altimeter for everything.
Randy

Offline galfert

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #37 on: February 17, 2019, 12:48:17 PM »
Hi all,
Just set up my brandnew Bresser DMAX 6-IN-1 Weatherstation with built-in wifi :) It all works fine, but in WeatherUnderground the relative air pressure is shown instead of the absolute air pressure as I have on my console. How can I change it so that WU gives the absolute air pressure? All stations in the far neighbourhood give absolute pressure, so my value is a bit weird in comparison with the others.
Anyone here willing to help me out? Thanks in advance!
Ronny

FYI - Your Bresser DMAX 6-IN-1 weather station is the same as the Ambient Weather WS-8478A. or sometimes just referred to as WS-8478.
https://www.ambientweather.com/amws8478.html

Might be good to know as you then have more resources to look for and search the Internet of other people with same/similar hardware. You might already know this but having this information might help someone else.
« Last Edit: February 17, 2019, 12:50:07 PM by galfert »
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Offline Ronny St.

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #38 on: February 17, 2019, 01:19:16 PM »
Thanks for the tip, Galfert! I did not know it, but it means that, if wanted, I could also use other software for connection with the internet  :-P I had found out that it is also the same as the Garni 1055 Arcus 6-IN-1 WiFi, but I chose for the Bresser because of the extended warranty of 5 years. You never know that it might be handy.
 
The price shown for the Ambient in $ (240 $) is a lot less that what I payed for it (349 euro, so about 394 $ or almost the double) and that is the price I find also when ordering it in other European stores. Oh well, if it appears to be a good station that complies with my needs, then I have no problem paying a bit more.

For those who are interested (you nevetr know  ;) ) my station can be found athttps://www.wunderground.com/personal-weather-station/dashboard?ID=IRANST9#history and it is working fine! Glad I bought this one to replace my old Alecto WS-3000 that went dead after 8 years of loyal service. It is quite an improvement and a step to a higher level!

Offline galfert

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #39 on: February 17, 2019, 02:03:52 PM »
Yep that is a big improvement. The Alecto WS-3000 is like the old Ambient WS-1050, WS-1070, WS-1075 (not exactly sure which but in that line somewhere).

5 year warranty is impressive.
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Offline CW2274

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #40 on: February 17, 2019, 02:06:44 PM »
That's why I was wondering the accuracy. Were they doing the full calculation etc.?

It's gotta be a glitch on their end since you are sending the correct data via CWOP. I don't see why Mesowest can't compute SLP properly.

Thanks...I use altimeter for everything.
As I now understand what Randy is speaking of, I have the same SLP "errors" as he does. Perhaps (just sayin') they're not errors, but merely calculations that go above our pay-grades of comprehension. I truly don't know. All this does however, is reconfirm why I've chosen to exclusively use the altimeter for my outright comparisons, it's always an apples to apples pressure comparison without all the other factors gumming up the works. Not that that's a bad thing, it's just not for general consumption, i.e., using the KISS principal.

Offline openvista

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #41 on: February 17, 2019, 06:10:14 PM »
As I now understand what Randy is speaking of, I have the same SLP "errors" as he does. Perhaps (just sayin') they're not errors, but merely calculations that go above our pay-grades of comprehension. I truly don't know. All this does however, is reconfirm why I've chosen to exclusively use the altimeter for my outright comparisons, it's always an apples to apples pressure comparison without all the other factors gumming up the works. Not that that's a bad thing, it's just not for general consumption, i.e., using the KISS principal.

As far as I can see, I don't see any discrepancy between your SLP and KTUS. They were both 29.93 at last report (14:53 MST). All your pressure numbers appear dead on.
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Offline CW2274

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Re: WU: relative pressure shown instead of absolute, how can I fix that pls?
« Reply #42 on: February 17, 2019, 06:34:52 PM »
As I now understand what Randy is speaking of, I have the same SLP "errors" as he does. Perhaps (just sayin') they're not errors, but merely calculations that go above our pay-grades of comprehension. I truly don't know. All this does however, is reconfirm why I've chosen to exclusively use the altimeter for my outright comparisons, it's always an apples to apples pressure comparison without all the other factors gumming up the works. Not that that's a bad thing, it's just not for general consumption, i.e., using the KISS principal.

As far as I can see, I don't see any discrepancy between your SLP and KTUS. They were both 29.93 at last report (14:53 MST). All your pressure numbers appear dead on.
Yes, currently they are very similar. Go back to before sunrise, it tells a different story. The altimeters always match, not SLP.

 

anything