[wxqc] Barometer Tweaking

[Dave Helms]

Hi Chuck,

Altimeter corrects pressue to sea level so you do not have to account 
for elevation differences between your station and the reference 
station.  Just match the reported airport METAR altimeter pressure 
("QNH" XX.XX inches of Mercury (Hg) or "INS") to your corrected 
altimeter pressure.  Listen to the Amador METAR  report from its AWOS 
station by calling 209-257-1292 (this  is  on the airnav.com page). 

Dave
CW0351

P.S.  Near sea-level, pressure decreases about 0.001 inch of Mercury for 
every foot in the vertical.  Station pressure is only used when 
comparing two station's raw, uncorrected, station pressures.  Station 
pressure is not generally available from ASOS/AWOS stations.  In 
addition to requiring both (raw) station pressures in inches of Mercury, 
you also need both station's elevations in feet to do a comparison. 

Charles Bland wrote:

>Me and my Peet Bros Weather Station live in the Sierra Nevada mountains at 3500 
>ft AMSL.
>
>My nearest airport with AWOS is at approximately 1700 ft AMSL. 
>http://www.airnav.com/airport/O70
>
>So, when I calibrate my barometer AT THE AIRPORT, then take it home, the 
>reading always falls because of the elevation/air pressure change.
>
>My question is, how do I adjust the AWOS reading at the airport to compensate 
>for the elevation change to my house? Is there a ballpark number for air 
>pressure change as you change elevation?
>
>Chuck
>
>p.s. a recent power outage here really goofed my station, so if you look the 
>data quality page for me (CW4289) it is going to look REAL BAD. So, since my 
>station battery died and I lost a bunch of data, I took the opportunity to 
>solve my calibration problem on the barometer.
>
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