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Author Topic: Dew Point  (Read 6650 times)

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Offline daveq

  • Posts: 3,098
  • Hollywood, MD
    • Hollywood - St. Mary's County, Maryland
Dew Point
« on: June 12, 2005, 01:55:37 PM »
I've been send data to CWOP for about a month now.  Most of data is not too bad on CWOP QC graphs and the summary says it's within acceptable range but the Dew Point is very erratic.  If someone could look at it and give some suggestions on what I can do to improve I would appreciate it.  http://pond1.gladstonefamily.net:8080/cgi-bin/wxqchart.pl?site=C3754

--Dave

Offline Weather Display

  • Posts: 87,468
  • Davis VP2
  • New Zealand
    • Weather Display
Re: Dew Point
« Reply #1 on: June 12, 2005, 08:07:20 PM »
hi
the dew point is calculated from the temperature and humidity
your humidity is reading not too flash either...i.e the DP differences follow the humdity differences
the station type you are using does not have a very accurate humidity sensor (the ws2010)

Offline TNETWeather

  • Kevin Reed (KrelvinAZ)
  • Posts: 5,939
  • Gremlins are at work...
  • Mesa, AZ
    • TNET Weather Station - Mesa AZ
Re: Dew Point
« Reply #2 on: June 12, 2005, 08:17:34 PM »
My dew pt's are effected by the road next to the property.  When I moved the station, I had to put it closer to the edge of the property since there was no other place to put it.  Now my dew pts at night are spiked as a result.

All you need is Time, Aptitude and Desire ... and you can build just about anything...

Offline NorCal Dan

  • Dan - KJ6RGX
  • Posts: 10,580
  • Davis Vue/Win10
  • Ocean Park, WA.
    • Traveling RV Weather
Re: Dew Point
« Reply #3 on: June 12, 2005, 08:31:18 PM »
Are your readings that calculate the DP taken from the 2010 or VP2?  The VP2 with FARS should not be showing those spikes.  My VP2 with FARS graph for comparison...



The FARS should keep your readings consistent.  It looks like your spikes occur during daytime readings only...

Offline daveq

  • Posts: 3,098
  • Hollywood, MD
    • Hollywood - St. Mary's County, Maryland
Re: Dew Point
« Reply #4 on: June 12, 2005, 10:47:06 PM »
It's from the VP2.  I have it located about 5' above ground level but it is over some plants that are about 2' high and not the short grass as is suggested.  Didn't think it would make that much difference.  Will it?   I'm taking the WS-2010 out of my signature.  I don't even track it any longer.

Offline Weather Display

  • Posts: 87,468
  • Davis VP2
  • New Zealand
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Re: Dew Point
« Reply #5 on: June 12, 2005, 10:50:58 PM »
hummm
the stations that the quality control is checked against....how do you know they are accurate too??

Offline daveq

  • Posts: 3,098
  • Hollywood, MD
    • Hollywood - St. Mary's County, Maryland
Re: Dew Point
« Reply #6 on: June 12, 2005, 10:58:16 PM »
Brian, I don't know about their accuracy.  I'm just going by the CWOP comparison.  Could a combination of the variance in the temp and humidity recorded be causing the spikes?  If you look at my page you'll see they are not very smooth.

Offline Weather Display

  • Posts: 87,468
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  • New Zealand
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Re: Dew Point
« Reply #7 on: June 12, 2005, 11:14:29 PM »
yes

Offline daveq

  • Posts: 3,098
  • Hollywood, MD
    • Hollywood - St. Mary's County, Maryland
Re: Dew Point
« Reply #8 on: June 12, 2005, 11:24:57 PM »
Is there a way of smoothing them?  Or would that effect the accuray even more?  Something like you did for the wind speed.  That really made a difference in the apperance of the graph.

Offline Weather Display

  • Posts: 87,468
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  • New Zealand
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Re: Dew Point
« Reply #9 on: June 12, 2005, 11:27:29 PM »
i dont think that would do much....that would not affect some underlying reason for having an incorrect temperature and humidity reading in the first place....(and a resulting dew point (although if your temperaure is reading too high, then your humdity will read too low...and so the DP still should be reasonable)

in 10.25p I now have a 1 hour smooth added to the year to date graph (via graph history)
for temperature/humdity and dew point..
looks much better

Offline hydrowx

  • Bill
  • Posts: 1,610
  • Northeast Illinois USA
    • Goose Lake Weather
Re: Dew Point
« Reply #10 on: June 12, 2005, 11:39:55 PM »
Dewpoint is one of the most variable parameters measured in CWOP. Most of the dewpoints in home wx stations are calculated and not measured directly. I looked at your 28 day comparison and you were within tolerance at:

http://weather.gladstonefamily.net/site/C3754

If you really want to try and compare nearby sites I would try around the middle of a windy day when the air has really been mixed out to compensate for any localized effects. The QC data provided by the CWOP site is a great service...I refer to it a lot...but you have to be sure the nearby sites are accurate as well. My location is getting flagged for dewpoint but the nearest site to mine is an AWOS that has been reporting dew points several degrees above the surrounding ASOS and AWOS locations. I compare my own site with a sling psychrometer.
Bill


Davis VP2+

Offline Weather Display

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Re: Dew Point
« Reply #11 on: June 12, 2005, 11:43:17 PM »
yes, very good points!

Offline NorCal Dan

  • Dan - KJ6RGX
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  • Ocean Park, WA.
    • Traveling RV Weather
Re: Dew Point
« Reply #12 on: June 12, 2005, 11:52:45 PM »
One last thought...I had to reset the batteries in my FARS after it arrived, shipping had apparently rocked them loose enough that they weren't taking a charge from the solar panel.   

Offline daveq

  • Posts: 3,098
  • Hollywood, MD
    • Hollywood - St. Mary's County, Maryland
Re: Dew Point
« Reply #13 on: June 13, 2005, 12:19:00 AM »
I just checked, my fan is running.  But I'll check in the morning before work.  If they aren't fully charging they'll most likely be dead by then.  One thing about this area.  Many of the stations I've checked may be on the water or at least closer to it than I am.  This area has several rivers and large creeks plus the Chesapeake Bay is about 5 miles from me.  I know for sure four within a radius of 12 miles are on the water.  I often see a temp reading of 8-10 degrees difference between them and my station.  They are also more exposed than I am.  My house is surrounded by tall oak and popular.  I've had winds 1-2 mph and they are seeing 15-20.  I'm going to look into a sling psychrometer.  It is almost Father's Day.