CWOP Pressure different then WU

[ryan810cows]

I have been looking for a solution to this for a while now. My Wunderground pressure shows differently them my CWOP and my CWOP is incorrect according to Gladstone (I have and "X" & (2) Thumbs Down). How can I calibrate my CWOP Data?

Wunderground Site
http://www.wunderground.com/weatherstat ... =KVACHRIS6

CWOP Site
http://www.findu.com/cgi-bin/find.cgi?call=CW2722

Quality Report Info
http://weather.gladstonefamily.net/site ... nformation


I'm using Windows XP and have a Vantage Vue. I'm running 1.9.4 Cumulus.

[steve]

CWOP pressure and WU pressure should be different. CWOP require altimeter pressure rather than MSLP, so Cumulus calculates (an approximation to) that using information it gets from the console.

So, firstly, have you configured your altitude correctly in both Cumulus and the console?

If you have, this may be the potential issue that Ted Lum mentioned recently. Apparently the Vue has the option of displaying altimeter pressure on its screen rather than MSLP (with the VP2 you don't get a choice). Rather oddly, the displayed setting also affects the pressure which is read by software. So this screws up the altimeter pressure calculation. What do you have your console set to?

[ryan810cows]

I just changed my Pressure setting from NOAA to ALTIMETER SETTINGS. I read somewhere else that could be an issue. My numbers didn't change all that much. It went from 29.91in to 29.87in.

Yes, my altitude is set correctly in both Cumulus and the console.

I am also having to "Calibrate" cumulus on the press as well about 2.18in in order for cumulus to send the pressure that is displayed on my WX to Wunderground. Not sure about that one either.

CWOP is still getting wrong info. ALMOST looks like its getting my ABSOLUTE PRESSURE but its off by 00.01in.

Anything else I can try?

[rci136]

What is the reading from the Davis console itself?

[ryan810cows]

Ok. So I think all is OK. You where right. I had to have it set on ALT not NOAA.

CWOP is now getting what I see on my WX.

WU is now getting what I DON'T see (I think) on my WX which is NOAA.

I was also able to zero out the Cumulus calibration numbers too. I may have not given everything enough time to clear itself out.

I hope I'm explaining my self correctly. If something changes, I'll post again.

Thanks for the help!

[ryan810cows]

FYI.. Some numbers...

My Elevation is 2091ft

My WX is reading 29.90in for Barometric Pressure.
My WX is reading 29.90in for ALTIMETER Setting.
My WX is reading 27.71in for ABSOLUTE Pressing.

CWOP is now getting 29.90in
Wunderground is now getting 29.95in
Cumulus is now getting 29.95in


My WX Site:
http://daviswx.blogspot.com/

My CWOP Site:
http://www.findu.com/cgi-bin/find.cgi?call=CW2722

My Wunderground Site:
http://www.wunderground.com/weatherstat ... =KVACHRIS6


Thanks again!

[rci136]

That is looking a lot better!

http://mesowest.utah.edu/cgi-bin/droman ... ?stn=C2722

[steve]

That just leaves me as confused as ever. From what I have been told about the Vue, I would have expected you to have needed it set to NOAA (which is apparently the same as a VP2), and then (apparently) that's the value that would be sent to Cumulus, and then the conversion to altimeter which Cumulus does would work correctly, as it does on a VP2.

[SpaceWalker]

From the Davis Instruments Vantage Vue documentation:

• "In reality, the Vantage Vue measures atmospheric pressure. When you enter your location’s altitude in Setup Mode, the Vantage Vue stores the necessary offset value to consistently translate atmospheric pressure into barometric pressure."

From the Davis Instruments Vantage Pro2 documentation:

• "In reality, the Vantage Pro2 measures atmospheric pressure. When you enter your location’s altitude in Setup Mode, the Vantage Pro2 stores the necessary offset value to consistently translate atmospheric pressure into barometric pressure."

From what I have been told about the Vue, I would have expected you to have needed it set to NOAA (which is apparently the same as a VP2), and then (apparently) that's the value that would be sent to Cumulus, and then the conversion to altimeter which Cumulus does would work correctly, as it does on a VP2.

The initial settings are the same for both the Vantage Vue and the Vantage Pro2:

• "Before calibrating the barometric pressure, be sure the station is set to the correct elevation. Find the nearest source of
  barometric pressure, such as a local airport, to get a current barometric pressure."

So, yes, Steve your expectations were right.

The pressure information provided by an airport or a METAR is "the current barometric pressure extrapolated to sea level".

Here is an example of a METAR (Stanfield International Airport):

• CYHZ 150900Z 21022G30KT 1SM R14/P6000FT/D -DZ BR VV002 09/09 A2953 RMK FG8 SLP003

where:

• altimeter pressure: 'A2953' to represent '29.53 inches Hg'
  sea level pressure: 'SLP003' to represent '1000.3 mb'

ryan810cows should look at the information provided by KBCB (in Blacksburg, Virginia) - for more accurate information, north american members can have a look at CheckWX Aviation Weather