Topic: ASOS visit with VP2 in hand

[ValentineWeather]

Visited ASOS today for comparison with my portable 24 hr. VP2 with SHT31 temp/humidity sensor. I collected 40 minutes of data but temperature wasn't changing much and unfortunately the 5 minute data from ASOS skipped most sections  when there.... I took pictures of console every 5 minutes but will only provide the 2 times I received ASOS data.

The ASOS was reading +1F on one of the 5 minute intervals and the other time period both reported 91F. You can see the ASOS does read lower dewpoint /humidity as some that watch ASOS stations may have suspected.  -4° DP which ends up being 6% humidity in 90-91F range.

Anyway thought I would give what I found. What I would really like to do is several full days of side by side comparison but this sample told me some of what I suspected.

[CW2274]

You can see the ASOS does read lower dewpoint /humidity as some that watch ASOS stations may have suspected.  -4° DP which ends up being 6% humidity in 90-91F range.

Somewhat surprised by this...granted a very small sampling though.

[ValentineWeather]

You can see the ASOS does read lower dewpoint /humidity as some that watch ASOS stations may have suspected.  -4° DP which ends up being 6% humidity in 90-91F range.

Somewhat surprised by this...granted a very small sampling though.

Really? Almost forgot that's why you always end up in QC jail.   
I wonder now if the issue you have isn't when DP/temp gets the big separation with sub 10% humidity.  I'm always about 4° higher on DP. But then again each ASOS may be different but they aren't suppose to be.  Remember the the debacle with the HO83 shield. I read somewhere recently they still haven't got all the bad HO83's out of field yet. https://wattsupwiththat.com/2008/01/10/inside-the-asos-ho83-tempdewpoint-sensor/

[WheatonRon]

All I can say is, "very interesting" as used in the TV series, Laugh in, I believe! A portable VP2--must try that sometime! Maybe Davis is working on such a product--oops, sorry--I forgot that they are working on the VP3!

[CW2274]

You can see the ASOS does read lower dewpoint /humidity as some that watch ASOS stations may have suspected.  -4° DP which ends up being 6% humidity in 90-91F range.

Somewhat surprised by this...granted a very small sampling though.

Really? Almost forgot that's why you always end up in QC jail.   

Only when the humidity gets below 2% does the 31's dew crash, otherwise it's completely comparable to my usual check points.
I think that the 31 has trouble way down low, just like about every sensor has problems way up high (asos's included).

[ValentineWeather]

I only took the shield, without anemometer or rain gauge but it could be easily attached. I would take a picture but it's all broke down and put away.
I clamp shield on 6' pipe that fits down in holder for dish. They call these non penetrating platform and looks just like this. You can weigh it down with cement blocks if needed.

[CW2274]

 

[ValentineWeather]

Some may remember my theory about in town with grass and trees being cooler during summer.

I just got back from airport 2nd time and can confirm anywhere from +2-4° warmer at airport with same matching Davis SHT-31's instruments I'm using in town. Amazing what grass and trees can do. The airport may be +1° warmer than SHT31 at times but taking accuracy of instruments into consideration it's within specs if Airport was + 1/2 degree and SHT31 - 1/2 degree.

I guess I can't complain ASOS is reading hot. 

[CW2274]

Some may remember my theory about in town with grass and trees being cooler during summer.
 

I'm quite sure that Central Park in NYC (just as one example) is several degrees cooler than the surrounding area.

[ValentineWeather]

Some may remember my theory about in town with grass and trees being cooler during summer.
 

I'm quite sure that Central Park in NYC (just as one example) is several degrees cooler than the surrounding area.

I'm sure it is.
I guess the issue that pushed me into checking this for myself is my neighbor telling me why was the airport 97° and you are only 93°. My thermometer under house eve was also 97° today.  When I try to explain it's because your thermometer is against the house in a heat pocket the response is well it's the same as airport. 

[CW2274]

Some may remember my theory about in town with grass and trees being cooler during summer.
 

I'm quite sure that Central Park in NYC (just as one example) is several degrees cooler than the surrounding area.

When I try to explain it's because your thermometer is against the house in a heat pocket the response is well it's the same as airport. 

Many just don't get it, nor care to.

[openvista]

Interesting! I also noticed that the pressure readings were very close. Did you adjust the elevation or did it just happen to work out? Since the VP2 console doesn't do altimeter and it was so warm, I would have expected there to be an appreciable difference between the two readings (MSLP vs QNH).

[ValentineWeather]

The altimeter I just used the zero elevation method and matched airport. I haven't touched pressure on the VP2 console for years but it's still very close.  I use the VUE console as my primary unit because it does have altimeter and usually dead on.

[CW2274]

The altimeter I just used the zero elevation method and matched airport. I haven't touched pressure on the VP2 console for years but it's still very close.  I use the VUE console as my primary unit because it does have altimeter and usually dead on.

This works well for the VP2 console in lieu of not having a Vue for the actual altimeter. As long as you're not in quite relatively high or low pressure, the VP2 is very close.

[ocala]

Well, you were a couple hundred feet away. Micro climate?
Just sayin.

[ValentineWeather]

Well, you were a couple hundred feet away. Micro climate?
Just sayin.

 

[CW2274]

Well, you were a couple hundred feet away. Micro climate?
Just sayin.

The only micro-climate (and think this term is pushing it here) that could apply at this short distance would be wind velocity/direction at any given moment and rainfall. Temp and humidity should be virtually identical.

[ValentineWeather]

I took it as a joke. We had a nice steady breeze so I'm pretty sure it was representative of conditions 100 yards away. 
Its also flat as a pancake .....

[CW2274]

I took it as a joke.

Oh....yeah. I get too wrapped up in this stuff sometimes.

[ValentineWeather]

I took it as a joke.

Oh....yeah. I get too wrapped up in this stuff sometimes.

I forgive you 

[WheatonRon]

I took it as a joke.

Oh....yeah. I get too wrapped up in this stuff sometimes.

I forgive you 

You shouldn't forgive a Penguins fan!

[alexstaar]

Also bear in mind that if your station is set up in a locale with more vegetation (i.e. trees, shrubs, irrigated grass, etc.) such as a neighborhood/subdivision than at an open and exposed location like an airport/airfield, you will have a lot more transpiration of water vapor from the vegetation leading to locally higher vapor pressure, relative humidity, dewpoint, etc. With this considered, air with a higher water vapor content heats less efficiently than air with lower water vapor content. So there may very well be discrepancies this manner as well.

[ValentineWeather]

Also bear in mind that if your station is set up in a locale with more vegetation (i.e. trees, shrubs, irrigated grass, etc.) such as a neighborhood/subdivision than at an open and exposed location like an airport/airfield, you will have a lot more transpiration of water vapor from the vegetation leading to locally higher vapor pressure, relative humidity, dewpoint, etc. With this considered, air with a higher water vapor content heats less efficiently than air with lower water vapor content. So there may very well be discrepancies this manner as well.

Absolutely I'm located on a very densely vegetated side of town including a creek nearby.

[ValentineWeather]

Ran across tripod I had stored away. This is a better way of mounting VP2 shield on pvc pipe and using tent stakes for stability in wind.

[ValentineWeather]

Very hot day set a station record 106°. Took the portable back out to airport and matching 108° at 240pm. Didn't stay long it was too HOT!