VP2 and CWOP QC temperature check

[JMM411]

Sorry about the long post.  I registered my station with CWOP two weeks ago:  http://weather.gladstonefamily.net/site/D3370?lat=39.65845&lng=-76.94720

The CWOP quality checks started out with green checks on all parameters.  My night time temperatures have consistently been cooler than average, although they passed the QC check previously.  The past two days, they’ve been out of acceptable limits and received the red "X".  While I’ve read enough forum posts and emails at wxqc to know I shouldn’t be overly concerned yet, I don't want to send faulty data.  Since I'm new to this, I'm wondering what I can do better.

We are in the country, surrounded by pastures and farm fields.  The topography is a shallow valley with rolling hills.  The front of my property is in the bottom of the valley.  The rear-most lot line extends about halfway up the side of the valley wall.  From rear to front, the elevation drops about 90 feet.  The weather station is situated along the rear lot line.  Behind the station is a pasture, behind that a corn field, both sloping upwards to the top of the valley side.  To the sides of the station is open ground for several hundred feet.  To the front is mostly open yard for 200 feet, then the house, then 400 feet of sharply sloping open front yard.

The station is a Davis Vantage Pro 2 with a 24 hour fan aspirated radiation shield.  It’s temporarily mounted on a tripod with the bottom of the shield 5 feet above mowed grass.  The anemometer is mounted at 10 feet for surveying wind at that level for possibly installing a vertical axis wind turbine.  Once the survey is done, the station will be permanently mounted and the anemometer installed at the correct height. 

 At night, cool, damp air flows down the hillside behind the house to the low area in the front yard.  I believe my temperature data is reflecting this flow, and while that makes it an outlier for the QC checks, I believe it is accurate for this location.   I’ve been comparing it to two other thermometers in my back yard and temps are consistent among all three.  I wondered briefly if the fan could be drawing in too much cool air at night, but the other thermometers are out in the open and reflect the same temps. What else can I do to validate my data?  If I believe it to be accurate, do I need to do anything about it?  It seems confusing: if I don’t do anything, my data appears to be wrong which then appears to be faulty data going to MADIS, even though the data may be right.  How do they know what’s right and what’s wrong?

[bcavnaugh]

http://weather.gladstonefamily.net/site/D3370?tile=10;days=2#Data
Show OK, I would wait for at lest 2 weeks and then compair.
I have nothing but trouble with Temp as well and for 6 years can't get OK from this site.
Trees are my problem.


NDS Weather

http://weather.gladstonefamily.net/site/C4784?tile=10;days=2#Data
http://weather.gladstonefamily.net/site/C4784?tile=10;days=56#Data

[George Richardson]

I have never answered a post this unequivocally.
You are RIGHT: they are WRONG: don't worry about it!

" I’ve been comparing it to two other thermometers in my back yard and temps are consistent among all three."
Thats the reason!

CWOP is good as a guide, a reference tool, but they are using a computerized interpolation of data from many locations (which they will not share with you) and of questionable integrity. It is very possible that a new, low quality, badly sited station was added to the CWOP "pot" in your area a couple of days ago and their VERY bad data is affecting your excellent data.

Get you a sling psychrometer and test your equipment, get a 4" manual rain gage ant test your tipping bucket then kick back and enjoy!

George

[JMM411]

Thanks! This has been my little corner of the world for 22 years and I know it typically is cooler here than in nearby areas, especially the suburbs and especially in the evenings.  There are several weather stations in the area, but their situations are all different than here, so it's hard to make a direct comparison.  The station at the airport 4 miles away is surrounded by level ground.  Another station is in a housing development sheltered by surrounding houses.  Another is mounted high on a ham radio tower above the roof.  The weather here is what it is, I just want to be sure my station reflects that accurately.  If CWOP and MADIS are ok with being "a little off" when compared to other stations, and as long as my readings are accurate for here, I'm ok with the red "X"s (even Camp David had red "X"s.)  Any recommendations on instruments to use to validate readings and where to get them?

[floodcaster]

I applaud you for taking such an interest in providing the most accurate data possible. I agree that your readings seem to be accurately indicating conditions in your microclimate and would not be too concerned with the cwop qc since you've verified the readings with other thermometers.

I have similar issues with dewpoint on occasion but have verified my readings with a sling psychrometer. The only thing about a sling is the visual readings don't allow for much precision. A digital readout would be better, but the cost is higher.

[WeatherGoose]

CWOPs Madis QC system is a TOTAL JOKE!

As others have already pointed out, their system for cross checking your data with surrounding stations is questionable at best!

I have a vintage professional grade thermometer and use it compare the readings I get from my VP2 and they are almost always spot on with each other.  However, according to CWOP, my temps are 3-5 degrees colder than they are supposed to be most evenings and on sunny hot days.  (I have a daytime FARS on mine)

I don't know who came up with the QC system that they use, but for the most part, the QC reports are useless and the temps they claim to be correct are laughably wrong most of the time.

So... Don't lose any sleep over what your QC stuff says.

As long as you get TWO THUMBS UP most of the time, you have nothing to worry about.  IGNORE their siting alerts and the RED OUT OF RANGE messages.  THEY ARE WRONG!

The Davis VP2 is one of the most accurate stations around.  Unfortunately, there are far more CWOP stations using something with far less quality than a VP2.  Therein lies the problem with CWOPs QC system.

Like someone else said... All it takes are a couple of BOZOs in your area with some cheapass, unshielded Wal-Mart special to screw up all the local data.

[ocala]

I agree with WeatherGoose here to a point.
There really isn't any other way to compare data other then taking a sampling of surrounding stations. They have no way of knowing what particular factors affect each micro-climate. If one station is an outlier they can't email them and tell them to fix it. Although you would think there would be an alarm for stations way off the mark.
Bottom line, as mentioned above, if you know your readings are correct then that's all that's important. Don't get caught up by the red X's. They don't mean anything.

[Sigdigit]

Hah!  I'm not the only one with valley effect! I too am at the bottom of a valley and cool damp air collects real quick around sunset.  Initially I got a few CWOP less than two thumbs up, but eventually their program realized what was going on over time and reported that it appears my sensor is located in a valley.  I have the same equipment.  You can check my stats at CWOP using DW2180.  Depending on other conditions, I can be the same as surrounding stations, or up to 10 degrees cooler!  This is especially prevalent in winter.

[WeatherGoose]

Hah!  I'm not the only one with valley effect! I too am at the bottom of a valley and cool damp air collects real quick around sunset.  Initially I got a few CWOP less than two thumbs up, but eventually their program realized what was going on over time and reported that it appears my sensor is located in a valley.  I have the same equipment.  You can check my stats at CWOP using DW2180.  Depending on other conditions, I can be the same as surrounding stations, or up to 10 degrees cooler!  This is especially prevalent in winter.

Yep!  We are in a valley micro-climate too.  A lot of time my MADIS QC would acknowledge this with that message that mentions it, saying that our readings are "likely" to be correct.  But a week or so later, it would be right back to the RED text warnings, the RED X saying our siting is wrong, or that we need to adjust our dewpoint 3-4 points!  

Early on in my experience with CWOP, all of this was VERY confusing.  But over time, I have learned that it is the MADIS QC data that needs fixing, NOT my station location, station settings, or accuracy.

Frankly, in my opinion, I think CWOP should just do away with the entire QC process as long as they are unwilling to fix it.  I unsubscribed to the QC emails months ago, and have removed all my bookmarks to those pages.  I haven't checked my stats in months and have no plans to ever refer to them again.

I know that my station is accurate based on my own checks, and since I own a VP2, I trust my data far more than any of the other PWS in the area.  It is really too bad, since a QC system that actually worked would be a very valuable tool for station owners.

[JMM411]

I have to admit, I was excited to get the green "thumbs up" the first few days my station was up.  The red "X" bothered me at first, because I want my data to be as accurate as it can be.  With that said, I soon realized that it IS as accurate as it can be...for whomever happens to care about what the temperature is in my back yard.  The QC soon caught on and posted a note about the station being sited in a valley, so I'm ok with their findings.  As others who live in similar settings know, you can walk a few feet one way or the other and find yourself in a pocket of cool air.  Walk a few more feet and you'll be out of it again.  It's a micro climate and my station is documenting what goes on here.  This is a hobby (albeit an expensive one) and I try to keep that in mind.  I'm really glad I found this forum, it's been a huge help.  I'm building a rain gauge heater now with ideas from some of the other posts.