[wxqc] Temperature "errors"

Sun Sep 25 15:59:12 EDT 2005

Allan,

Chances are your dewpoint is OK. There are a few ways to check this.

1.) If you are weather savvy, I would seriously consider investing in 
a sling psychrometer. This instrument is a (typically mecury, 
sometimes alcohol) set of two thermometers connected on a metal/wooden 
slat to a freely rotating handle. The bottom of one of the 
thermometers is covered in a cloth "sock" which you wet. By spinning 
the thermometers for a minute or two, you measure temperature with one 
and wet-bult temperature with the other as the water evaporates from 
the sock. The two end numbers can then be used to calculate the 
dewpoint.

I use this all the time to make sure my instruments are calibrated. 

2.) In mid afternoon on a sunny/breezy day, once the atmosphere has 
mixed out the elevation differences, check your dewpoint against 
surrounding airport sites. Assuming there are no strong cold fronts in 
the area, you should see a number within a degree or two. 

If there's a strong difference (and I will look into it with you as 
well), I would recommend getting a replacement instrument from Davis. 
There is a certain degree of inaccuracy with these digital 
instruments, but Davis leads the way in data quality of low-cost 
weather stations and it should be darn near what you expect from a 
manual reading. A number of users would suggest calibrating the 
dewpoint/RH sensor, but I am strongly against this. Unless you are 
100% sure that the error is a bias error, you run the risk of masking 
a greater problem with the weather station.

Hope this helps!
Evan
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Evan you seem to be the right person to direct this to. I originally sent it
to Dave Helms.

Dave, I am having a problem getting my dewpoint data to fit the criteria of
CWOP. I have a Davis Vantage Pro with the wireless installation. I am not
having any wireless problems.  The sensors are sited over a grassy area with
at least 300 feet from any trees and about 5 feet off the ground on the
Davis tripod.. Sensors are the fan aspirated group housed in the Davis
supplied shield. Fan is set to run all the time. If you check my data
quality you will see that dewpoint is always off.  CW1490  I am about to
mount anemometer on a 30 foot telephone pole which should get more accurate
reading of wind speed.

 I am a fussy type of person and want to supply you all with the most
accurate data I can. Do you have any suggestions to help?  The only thing I
can think of is that we do have quite a lot of fog here due to the river
valley we are located in and that keeps it more moist here until it burns
off.  Thanks for any help you can give. Maybe I am trying to get my data to
fit when its just my location.

allan at vtstudio.com

www.vtstudio.com <http://www.vtstudio.com/> 

Regards

Allan Seymour

Vermont Studio

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<div class=3DSection1>

Evan you seem to be the right person to direct this =
to. I
originally sent it to Dave Helms.<o:p></o:p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

Dave, I am having a problem getting my dewpoint data =
to fit
the criteria of CWOP. I have a Davis Vantage Pro with the wireless
installation. I am not having any wireless problems.&nbsp; The sensors =
are
sited over a grassy area with at least 300 feet from any trees and about =
5 feet
off the ground on the <st1:place w:st=3D"on"><st1:City =
w:st=3D"on">Davis</st1:City></st1:place>
tripod.. Sensors are the fan aspirated group housed in the <st1:place =
w:st=3D"on"><st1:City
 w:st=3D"on">Davis</st1:City></st1:place> supplied shield. Fan is set to =
run all
the time. If you check my data quality you will see that dewpoint is =
always
off.&nbsp; CW1490&nbsp; I am about to mount anemometer on a 30 foot =
telephone
pole which should get more accurate reading of wind =
speed.<o:p></o:p>

&nbsp;I am a fussy type of person and want to supply =
you all
with the most accurate data I can. Do you have any suggestions to =
help?&nbsp;
The only thing I can think of is that we do have quite a lot of fog here =
due to
the river valley we are located in and that keeps it more moist here =
until it
burns off.&nbsp; Thanks for any help you can give. Maybe I am trying to =
get my
data to fit when its just my location.<o:p></o:p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><a href=3D"mailto:allan at vtstudio.com"
title=3D"mailto:allan at vtstudio.com">allan at vtstudio.com</a><o:p></o:p></sp=
an></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><a href=3D"http://www.vtstudio.com/"
title=3D"http://www.vtstudio.com/">www.vtstudio.com</a><o:p></o:p></span>=
</font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p>&nbsp;</o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Regards</span></font><o:p></o:p></p>

<p class=3DMsoNormal><st1:PersonName w:st=3D"on"><font size=3D3 =
color=3Dmaroon
 face=3D"Arial Black"><span style=3D'font-size:12.0pt;font-family:"Arial =
Black";
 color:maroon'>Allan =
Seymour</span></font></st1:PersonName><o:p></o:p></p>

<p class=3DMsoNormal><st1:State w:st=3D"on"><st1:place w:st=3D"on"><font =
size=3D3
  color=3Dmaroon face=3D"Arial Black"><span =
style=3D'font-size:12.0pt;font-family:
  "Arial =
Black";color:maroon'>Vermont</span></font></st1:place></st1:State><font
color=3Dmaroon face=3D"Arial Black"><span style=3D'font-family:"Arial =
Black";
color:maroon'> Studio</span></font><o:p></o:p></p>

<p class=3DMsoNormal><font size=3D3 face=3D"Times New Roman"><span =
style=3D'font-size:
12.0pt'><o:p>&nbsp;</o:p></span></font></p>

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