Topic: ASOS/AWOS Accuracy

[CW7491]

Thanks for the info. Is this SAWS/AWS part of ASOS as a backup system, or completely independent?

[CW7491]

Looks like I found an answer to my own question. It’s all in a name SAWS (Stand Alone Weather System). Effectively a backup weather system used by the FAA. News to me …

https://www.tc.faa.gov/its/worldpac/standards/faa-e-2935.pdf

[ASOSWX]

  The SAWS and AWS are FAA-owned equipment totally separate from the ASOS program.  SAWS came out late 90s. 
Hope this helped

[CW7491]

Thanks Joe!

[CW2274]

They are on a PMS like all FAA equipment, so I'm sure it's checked at least once a year. If it is off, this could potentially be critical with pilots now that icing conditions are becoming more prevalent.

There are quarterly, Semi-annual, and Annuals on the System.  The DTS1 is sent in every 18 months for calibration.

[ValentineWeather]

Too bad they can't fix the freezing fog from icing over the temperature sensor. It's happened twice now this winter on the KVTN ASOS. As it ices over, it warms. Why because it blankets the sensor in thick ice like it does everything else. They really need to go back to a naturally aspirated Stevenson Screen with a fan like they use in Canada, and other countries.  At least you can turn the fan off to prevent the sensor from becoming ice covered.
What happens is the RH goes up with the temperature separation (air and dew point), as you can see here. The actual air temperature was near the dew point temp (12°) with the thick ice fog. The dew point sensor is separate and non-aspirated, so was the only true indicator of temperature, with the near zero visibility at times.
 
NOAA just gave a contract to RM Young for their aspirated shield, another mistake. The RM Young is famous for sucking in heated exhaust during light wind and reading high, along with other issues. Just ask Jerry Graves he has one. They really should have considered the naturally aspirated baranidesign gen3 MeteoShield's as shield replacements. They follow the Stevenson Screen with a fan very closely, with extensive testing done by University of Vienna. 

[CW7491]

Interesting. I wonder if the wire mesh in the HO-1088 intake is helping the ice build. Do you have the Davis mesh installed at the intake? Any issues in those conditions? I also meant to ask if you applied any temp offset to match with the nimbus or if it matches well without one

[ValentineWeather]

Interesting. I wonder if the wire mesh in the HO-1088 intake is helping the ice build. Do you have the Davis mesh installed at the intake? Any issues in those conditions? I also meant to ask if you applied any temp offset to match with the nimbus or if it matches well without one

Don't know about the ASOS.  I don't run with the mesh on. The Davis aspirated also froze up just like the ASOS, didn't see the same rise, only a couple degrees vs the Nimbus using the Gill shield.  The only offset I use is for the humidity on the Davis. -5 and 1.10 on the multiplier.

[TheBushPilot]

The dew sensor is warmed so ice accretion is a non-issue. Those Young 43502s frequently experience the hoarfrost in the intake on the NYS mesonet too. Imagine they experience that issue on the OK Mesonet too. I’m not aware of a good way to eliminate the issue completely but I don’t think changing shielding methods (aspirated/non-aspirated) inconsistently would be a valid method. Too much variability. FARS are good until they aren’t.


Cheers

[CW7491]

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I could definitely see it being a problem especially if it’s already loaded up with stuff like this one

[drew1021]

I would hardly call that a screen

[ASOSWX]

On occasion, the chilled mirror on the 1088 will freeze up.  Usually with a really dirty mirror and moist conditions the heater on the mirror wouldn't keep up.  A good cure for that was to add a step to the cleaning mirror process.  Waxing the mirror made the water droplets much smaller and repelled impurities which really helped with that issue. 

[CW7491]

NWS Louisville had an intern who ended up doing a temperature study at KLEX due to long standing complaints from local news outlets that the airport temperatures were problematic. The intern compared the HO-1088 ASOS hygrothermometer to two nearby MetOne 076b shields. One a KY mesonet station and another a CRN station. The interesting part of his presentation isn’t necessarily the results of his comparison, but how it highlights the very loose tolerances on the ASOS instrument partly due to multiple standards (ie manufacturer, FAA, NWS, etc). The sudden, dramatic shifts in temperature for ASOS when the sensor is changed or calibrated also might explain some of the questions of members (Buick) who see unexplained differences in their data in comparison. It’s also interesting to hear how the NWS staff puts itself in pretzels trying to explain and defend something that’s just not really all that defensible for what is considered in this case (and many other cases) national climate sites. An improved system can’t come quick enough. Let’s also hope that the bureaucratic, conversion and rounding issues are addressed too.

For those who don’t have the time or interest in watching it all, an interesting discussion during the Q&A starts at about 28:45.
https://m.youtube.com/watch?v=Sd9JhBjaJGw

[TheBushPilot]

WOW is all I have to say.

[hofpwx]

NWS Louisville had an intern who ended up doing a temperature study at KLEX due to long standing complaints from local news outlets that the airport temperatures were problematic. The intern compared the HO-1088 ASOS hygrothermometer to two nearby MetOne 076b shields. One a KY mesonet station and another a CRN station. The interesting part of his presentation isn’t necessarily the results of his comparison, but how it highlights the very loose tolerances on the ASOS instrument partly due to multiple standards (ie manufacturer, FAA, NWS, etc). The sudden, dramatic shifts in temperature for ASOS when the sensor is changed or calibrated also might explain some of the questions of members (Buick) who see unexplained differences in their data in comparison. It’s also interesting to hear how the NWS staff puts itself in pretzels trying to explain and defend something that’s just not really all that defensible for what is considered in this case (and many other cases) national climate sites. An improved system can’t come quick enough. Let’s also hope that the bureaucratic, conversion and rounding issues are addressed too.

For those who don’t have the time or interest in watching it all, an interesting discussion during the Q&A starts at about 28:45.
https://m.youtube.com/watch?v=Sd9JhBjaJGw

Isn't the purpose of the USCRN to address siting and instrument issues and thus provide a baseline for comparison and correction?

[CW7491]

I know USCRN is designed to be the national standard for climate monitoring according to their website. Whether they intend to manipulate/correct weather data from ASOS climate sites using USCRN data is something I couldn’t speak to. I guess my point is that I’ve been surprised from researching it just how poor the tolerances are for ASOS, which are used as official climate sites, compared to the USCRN system and state run mesonets. The siting issues are what they are, but for the price of the system, it seems a temperature system with more accurate specs should be possible. To say nothing of the convoluted rounding and conversion processing. I’m hopeful that the new ASOS TRH system based on the HMP155 and RM Young shield will be an improvement, but it has run into delays. I also wish they had gone with the MetOne076b shield for temperature.

[drew1021]

My experience was the local ASOS ran high (+1.8f) and this continued for almost 6 years before they finally changed the temperature sensor out. I have a psycho-dyne reference thermometer and stood right by the ASOS and confirmed the error was there multiple times. Wish I had known who else to complain to at the time, so just blogged about it on my website.  One of the local North Platte meteorologist read the blog (I'll leave name off) so he convinced the tech to change the temp sensor because the max RH for KVTN over the past 6 years had never exceeded 93% so once the sensor got changed, BAM both issues fixed. Having the air temp read +1.8 prevented the RH from ever exceeding 93%.

This is precisely what’s happening at our local airport (KINT). I’ve informed the nws in Raleigh about it a few times over the past 3 years and yet they haven’t corrected the problem.

[ValentineWeather]

We're in big trouble, I think.  Why this globalist push to socialism, it's failed miserably everywhere.

[CW2274]

I believe it was Margret Thatcher that said, "socialism is fine til you run out of other people's money".

Never truer words spoken, and some still never learn.

[drew1021]

We're in big trouble, I think.  Why this globalist push to socialism, it's failed miserably everywhere.

Yeah not sure if this is what’s going on here, but your point is valid. I wonder if they’re purposely holding off on certain repairs on existing ASOS systems due to upcoming replacement of the temperature/dewpoint assy with the RM Young. But the reluctance to even look into the issue, in your case for 6 years, is beyond comprehension.

[hofpwx]

I believe it was Margret Thatcher that said, "socialism is fine til you run out of other people's money".

Never truer words spoken, and some still never learn.

The US is less than 2% of the total surface area of the Earth so the socialists aren’t doing it right.

[hofpwx]

I believe it was Margret Thatcher that said, "socialism is fine til you run out of other people's money".

Never truer words spoken, and some still never learn.

Also what Margaret Thatcher said:


https://www.margaretthatcher.org/document/107346

[CW2274]

I believe it was Margret Thatcher that said, "socialism is fine til you run out of other people's money".

Never truer words spoken, and some still never learn.

The US is less than 2% of the total surface area of the Earth so the socialists aren’t doing it right.

You said it.

[CW2274]

I believe it was Margret Thatcher that said, "socialism is fine til you run out of other people's money".

Never truer words spoken, and some still never learn.

Also what Margaret Thatcher said:


https://www.margaretthatcher.org/document/107346

So?

[hofpwx]

I believe it was Margret Thatcher that said, "socialism is fine til you run out of other people's money".

Never truer words spoken, and some still never learn.

Also what Margaret Thatcher said:
https://www.margaretthatcher.org/document/107346

So?

Just noting her acceptance and concern about environmental issues including climate change.