Topic: I need some advice regardings my reading

[anchorageweather]

Hello All:

Well, I've been getting my MADIS quality feedback for about a week now - and its become apparent that I have an issue with my dewpoint reading.

Here is a the quality readings for the last seven days (I started submitting to CWOP on about June 25):

http://weather.gladstonefamily.net/site/C8273?tile=10;days=7#Data

I'm assuming that to correct my dew point, I need to adjust my relative humidity level (I'm using Davis WeatherLink software).  Weatherlink doesn't let you adjust the dewpoint, just the RH?!? Does anyone know WHICH WAY to adjust the RH to get the dewpoint to work out? -  and by how much?  Also,  the station is in an area that is known for the DENSE area of trees relative to the surrounding community:


 
Could this affect the dew point?  Could the reading be correct - and I'm just different than my neighbors?

I guess I need to figure out two things:

How do I correct my RH, and should I correct my RH?

Thanks for any help!  

[Mark / Ohio]

The way I read the report your relative humidity is probably around 5% too high according to their error checking.  

The trees could be keeping the ground moisture higher in your area than surrounding stations out in full sun.  So your reading could be correct for your location.  Maybe your getting some humidity from the river as well.  The only way to know for sure would be to get a sling psychrometer and see how it's readings compare to the VPs.

[SLOweather]

I have 2 thoughts on this...

1) The Davis humidity sensor spec is accuracy to +- 3%, with an annual drift of 2% per year. You are just not that far off the spec to worry about.

2) Any time deviation from the Gladstone site stats come up I have to ask... If they are so accurate as to tell you that your numbers are off by a few percent, why bother running a weather station? Save a lot of money and time and just get your local conditions interpolated from them.

Granted, the site has a purpose, in showing gross variations from expected values (like a sensor in full sun, or a sea level BP correction that's not correct).  But the world is full of meteorologic variation and that's why we all have weather stations. Heck, here at SLOweather, some days I can see an honest 5 degrees F temp difference across 100' horizontally, and 10 degrees F across 100' vertically. That's a microclimate (maybe a nanoclimate ).

Like Mark said, trees, river, whatever. Those conditions are more likely what it really is right there right then, not what someone calculates that they they should be.

[Anthony]

I agree with Chris. Considering your readings are only off by 5% I wouldn't worry about it. I have a WMR-968 station and my readings are off my way more that that. Atleast when compared to the local metar. When compared to other PWS stations near by. They are a little closer. And to answer you questions about the trees. Yes they can effect your readings. They actually create their own little micro climate.

[Mark / Ohio]

....
2) Any time deviation from the Gladstone site stats come up I have to ask... If they are so accurate as to tell you that your numbers are off by a few percent, why bother running a weather station? Save a lot of money and time and just get your local conditions interpolated from them......

  Glad I'm not the only one with that passing thought from time to time.  

Since my VP1 ISS upgrade the new temperature sensor seems a bit more prone to radiation heating during the day than the old one.  (I don't have the fan.)  I backed the temp off 1 degree which cut my errors according to them down to an average 2-3 per day out of 90+ observations.  The errors that really bug me occur when there are scattered storms in the area.  They flag a 7°F or more error when I know darn well it was right at the time the cold down draft ahead of the storm hit or afterwords before the sun came back out.  

[anchorageweather]

I wanted to thank everyone for the feedback.  I guess I'll sit tight for a while - maybe see if I can find someone with a sling psychrometer around here that can tell me who's "correct"