Weather and the Internet > CWOP & APRSWXNET

Barometer/Altimeter Discrepency

(1/4) > >>

NorCal Dan:
My altimeter reading is much higher than the CWOP MADIS analysis line.
http://weather.gladstonefamily.net/cgi-bin/wxqchart.pl?site=D1695

I have spent days researching the problem.  The closest ASOS station to me is reporting similar altimeter readings.  But all other ASOS stations are reporting much lower altimeter readings.  Unfortunately, none of them are at or near my altitude.
http://weather.gladstonefamily.net/site/D1695?asosonly=1;tile=10;days=7#Data  
All the ASOS stations are listed at the bottom of that page.

Another problem I have found is that when WD is set to send altimeter data to CWOP it is NOT adjustable.  WD uses the raw station pressure (SLP) to calculate the altimeter pressure.  The only way I can think of to make any adjustment is to change the altitude setting in the Vue console as none of the offsets in WD will affect the altimeter reading.

My conclusions -- Either my Vue console barometer needs to be adjusted (not sure its possible or how to do it), or, all the stations I am being compared with are NOT sending true altimeter pressure readings.  I am NOT an expert, so if anyone has an idea I am all ears.


Add: WUnderground stations and barometer readings::

Condon Park - 29.80  (2500')
Banner Mtn. - 29.85  (3280')
Forest Knolls - 29.78  (3196')
Cedar Ridge - 27.20  (2800')
Cape Horn Colfax - 29.83  (2850')

Assuming these are NOAA barometer readings then my station showing 29.81 at 2428' is not out of line.

KeithW:
Personally, I do not pay any attention to the Gladstonefamily.net analysis; I think he is
way off or there is some error in the calculations. For example, my temperature and baro
readings nearly exactly track his "analysis", yet my station is flagged with his big red X,
while I get two thumbs up from MADIS.

I just don't bother trying to adjust my station data to match his "analysis". FWIW and YMMV,
of course.

-Keith

NorCal Dan:
Don't get me wrong...I am NOT adjusting my data to match the analysis.  AFAIK, my data is correct and everybody else is wrong  :wink:

Besides the closest ASOS airport matching my data I did find one other station that is close to my readings.  I emailed a bunch of the closest stations and received 4 replies so far...all but 1 claim to be sending altimeter pressure...and 1 guy is running the original VP under Lightsoft Weather Center software on a Mac computer and all he set was his altitude on the console, he's not sure the software is sending altimeter pressure.

I am going to contact DAVIS and see how much it would cost to NIST my console and sensors, or swap out my station for a NIST station, not sure how they do it or if that is even an option with the Vue.

niko:
Just to put this in perspective, if I read the spec correctly the NIST calibration will get it within +/- 0.03 inch Hg, which I calculate as +/- 1 millibar, and the discrepancy in CWOP is approx + 2 millibar.

niko:
I checked the quality reports for the 10 nearby sites listed on your CWOP analysis:

These 5 are worth something:

AR335, the only station that matches the analysis plot.
CW5488 the plots are OK, station readings low.
CW0713 the data has some problems, but the trend is that the station readings are high.
CW1789 plots are OK, station readings low.
KAUN plots are OK, station readings are high - but that's Auburn airport, and if that doesn't match the analysis :dontknow:

The other 5 are (IMHO) not worth much:

AS856 the analysis curve is ridiculous.
DS2319 the analysis curve isn't much better.
C1397 the analysis and data plots are bad.
AT999 the data is bad.
CW6842 analysis plot is bad.

I understand your frustration with this, but I guess I wouldn't lose too much sleep over it myself  :(

Navigation

[0] Message Index

[#] Next page