Weather Related Organizations > CWOP Forum
Davis Vantage Pro 2 "Barometer" and CWOP
NiceBill:
Hi Gang,
I am doing a study as to how my Davis baromiter and MADIS get along. I started this study a bit late in the month of Aug., but I plan on going through the winter. It should prove to be interesting. The month of Aug. went quite well. I hope you can read this report, I will add a mo. by mo. update to this post.
Bill.>>>>>>>>>>>>>>>>> :-)
This is a study with 4 of the stations used by MADIS QA to reflect my % of accuracy, of barometric pressures reported. The barometer in use is a Davis, enclosed in an Envoy. The stations are located at airports. Bloomington-KBMI 20 mi.. N., Champaign-KCMI 30 mi. E., Decatur-KDEC 20 mi. S., Lincoln-KAAA 20 mi. W. ME-CW9625. No sensors have been or wil be changed or recalibrated during the study period. 8-2008 A=average E=error Mb.
DATE Bloom. Champ. Dec. Linc. Me 3 Day % A --- E
8-1 N/A
8-2 N/A
8-3 N/A
8-4 N/A
8-5 N/A
8-6 N/A
8-7 N/A
8-8 START 8-9
8-9 29.99 29.99 30.00 30.01 30.01 100 0.5~0.5
8-10 30.02 30.01 30.01 30.02 30.04 100 0.2~0.3
8-11 30.08 30.06 30.08 30.09 30.11 100 0.2~0.3
8-12 29.93 29.94 29.94 29.93 29.97 100 0.2~0.4
8-13 29.85 29.86 29.86 29.86 29.87 100 -0.3~0.4
8-14 29.88 29.87 29.89 29.90 29.92 100 0.1~0.5
8-15 30.14 30.13 30.13 30.13 30.15 100 0.4~0.3
8-16 30.14 30.14 30.15 30.14 30.14 100 0.1~0.4
8-17 30.12 30.14 30.14 30.14 30.14 100 -0.4~0.4
8-18 30.04 30.06 30.07 30.06 30.07 100 -0.5~0.4
8-19 30.09 30.11 30.11 30.10 30.12 100 -0.1~0.3
8-20 30.11 30.11 30.10 30.10 30.11 100 -0.0~0.2
8-21 30.03 30.06 30.03 30.02 30.02 100 0.1~0.4
8-22 30.03 30.05 30.04 30.04 30.04 100 0.2~0.5
8-23 30.09 30.12 30.09 30.10 30.09 100 0.7~0.3
8-24 30.02 30.00 30.01 30.03 30.01 99 0.8~0.4
8-25 30.01 29.99 29.97 30.00 30.02 99 0.6~0.7
8-26 29.95 29.93 29.93 29.94 29.96 99 0.6~0.6
8-27 29.88 29.88 29.88 29.88 29.88 100 -0.2~0.3
8-28 29.80 29.83 29.82 29.80 29.81 100 -0.2~04
8-29 29.97 29.96 29.97 29.99 29.97 99 6.2~0.5
8-30 30.18 30.15 30.15 30.16 30.18 99 0.3~0.6
8-31 30.19 30.17 30.14 30.14 30.15 100 0.2~0.6
All readings taken at noon. W.H.S.
tinplate:
It's very important that you compare apples to apples. Airports report different barometer values for different purposes. One value is Sea Level Pressure (SLP). The other is altimeter. The VP console supplies (and displays) only SLP. CWOP, however, wants altimeter, so a number of software programs that submit to CWOP now convert the VP's SLP into an altimeter value and send that. Unless you are at sea level elevation, SLP and altimeter will be different values for the same location. For a comparison like you're doing, it would be best to compare altimeter. One reason is that the formula the davis console uses to convert the raw sensor pressure into SLP is different than the formula used by the equipment at the airports. This is because the NWS formulas are more involved, and contain custom correction factors for each location based on many years of historical data.
Steve
SoftWx
NiceBill:
Hi Steve, thank you for your reply.
I use the info. that is posted on my web page.
http://www.texasilweather.com/
That is SLP. However it gets to CWOP and converted to what ever they wish to do with it is fine with me.
I know one thing. The NWS station 20 mi west of me, adjoins the airport property in Lincoln IL. The NWS station has 3 barometers they use. They take the average of the three and that's what the corrected SLP is at the time of the reading. The pressure value at the NWS station is the same as the reading the airport reads.
I have checked the airports pressure and the NWS stations report many times and they are the same. I am the same at times and some times +- 0.01.
I don't think my comparison is to far off. I don't think CWOP is using SLP and altimeter readings at the same time to evaluate some ones station.
The graphs that are displayed on ther QA page are reflecting SLP.
Bill.>>>>>>>>>>>>> :-)
George Richardson:
Bill,
You ought to get VPLive from SoftWx to evaluate while you are doing a barometric pressure test. The price is right and it has 13 values reported relative to barometric pressure. I went through this barometric pressure morass when I first installed my VP2. Steve knows what he is talking about.
FWIW
George
NiceBill:
Thanks for the note George, I do understand.
I have two Calibrated Aneroid Barometers, at a cost of $400.00 each that I also use. The Davis barometer is dead nuts on with them. My interest is in why MADIS will vary so much at times. I have had my evaluation as low as 68%, so now I am watching it.
What I find very interesting, although I am not recording it, is the fact that I can receive a 98% evaluation for 7 days, however for the 3 day evaluation during the 7 day period I get a 100% evaluation.
edit: Maybe I should note: for 3; 3 day periods in a row I get a 100% report, during the same 7 day period at 98% #-o
Bill.>>>>>>>>>>>> :-)
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