Author Topic: AWEKAS  (Read 1616 times)

Blicj11

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AWEKAS
« on: August 20, 2017, 12:12:31 AM »
This morning, after sending data to AWEKAS for more than two years, I received notice from them that they had turned off my barometric pressure reading because it is not set to sea level. They included a link to the weather reports from the closest airport, Salt Lake City. I sent them the following reply:

Code: [Select]
SLC is currently showing 1011.4 hPa at an elevation of 1286 metres.

My current pressure is 1008.5 hPa at an elevation of 2525 metres.

My station is 1239 metres higher in elevation and should therefore be lower in pressure than KSLC.

My air pressure data looks accurate to me.

This is their reply:

Code: [Select]
The altitude of the station is uninteresting all weather stations (and airports) measure at sea level.

Please adjust your barometer reading to sea level

I am confused. Is there a setting in WeatherCat that allows one to adjust the pressure to sea level? And if so, should I use it? I understand the difference between absolute pressure at sea level and adjusting for altitude but I assume that what i really want to know is the pressure where I live, not where I don't live.
Blick


xairbusdriver

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Re: AWEKAS
« Reply #1 on: August 20, 2017, 01:05:50 AM »
I get the pressure converted to sea level in my METAR reports. But that is really only used, as far as I know, for computing aircraft performance. For airlines, most of that is already done by company computer, often with the required data input from the METAR data, or by the crew with Automatic Terminal Information System, and a laptop/tablet. I think most crews will be using charts as a back up, of course.

The "current" NWS weather report for Memphis shows 29.93 in/Hg as of 5:54 local (nearly an hour old. That agrees with the METAR of almost exactly the same time. There is no "SLP" reported in the 'normal' Wx report, nor would I expect it! My station is reporting 29.88 on the hour, I suspect the newest NWS and METAR reports will show up any minute.

I'm not sure I even forward my info to AWEKAS. Nope, that probably accounts for my not getting that nasty email. [rolleyes2]
I'll check and see if the pressures change at the airport...

Good luck convincing them your data is good. "Different" doesn't always mean "Bad"! [lol]

elagache

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You've got me confused also! (Re: AWEKAS)
« Reply #2 on: August 20, 2017, 10:37:14 PM »
Dear Blick, X-Air, and WeatherCat troubleshooters,

This morning, after sending data to AWEKAS for more than two years, I received notice from them that they had turned off my barometric pressure reading because it is not set to sea level.

. . . .

I am confused. Is there a setting in WeatherCat that allows one to adjust the pressure to sea level? And if so, should I use it?

I checked the WeatherCat manual and there absolutely nothing you can set with respect to barometric pressure.  However, for a number of station models there is the cryptic comment:

"Please note, WeatherCat uses your altitude to calculate relative barometric pressure with this station – please be sure your altitude is correctly set in WeatherCat’s preferences."

That would suggest that Stu is correcting the barometric pressure for some stations and I would guess that is to adjust it for sea level.  However, this comment is not to be found for Davis stations.  I think there is a good reason though, the Davis stations do ask for your elevation.  I would guess that Davis is supposed to adjust the barometric pressure in the console?  Right in my Davis manual I find:

"Meteorologists standardize barometric pressure data to sea level so that surface readings are comparable, whether they're taken on a mountainside or by the sea.  To make this same standardization and ensure consistent readings enter your elevation in this screen."

This is part of the Davis console setup discussion.

Perhaps something has gotten out of whack in your console and elevation is missing?

Let us know what you come up with!

Cheers, Edouard

TechnoMonkey

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Re: AWEKAS
« Reply #3 on: August 21, 2017, 12:11:49 PM »
Preferences -> Misc2 -> Set Calibration Data

Blicj11

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Re: AWEKAS
« Reply #4 on: August 21, 2017, 04:42:28 PM »
Edouard:
I came up with the same conclusions you did. And I've had my elevation entered in the setup screen on my VP2 for years so I suspect that Davis does that conversion and that is why WeatherCat does not make any further adjustments for that brand.

TechnoMonkey:
Thanks for the reminder that the Cat allows everyone to calibrate their data should the need arise.

Davis Instruments
Just talked to Davis tech support. If you enter your elevation in the Davis setup screen, the pressure is adjusted for altitude and gives you the "altimeter setting" reading. If you do not enter an elevation, the pressure is not adjusted for altitude and gives you the "sea level" reading. According to Davis, both methods are used and you pick the one you want.

I copy this from a 12-year old post on another forum:

First - let's start with what is actually measured at weather stations - atmospheric pressure. As you know, the air pressure descreases rather rapidly with increasing height - so if we were to make a contour plot of station pressures - what we'd really see is a contour map of the terrain - with lower pressures at higher elevations. As you can guess - this isn't very practical for analyzing the surface weather patterns - so a method needed to be created which could remove the effect of the differences in elevation.

Two methods exist for achieving this - first is the altimeter setting, second is reduction to sea level pressure. The latter uses a math equation that requires knowledge of what the mean temperature would be of the air below the station all the way down to sea level elevation - essentially what we think the measured pressure would be if we could dig a hole down to the height of sea level and measure the station pressure there. Bad guesses as to what this temperature profile should look like can results in big errors in this calculation - so in regions of sharp terrain SLP values can still vary markedly and make analysis difficult. The altimeter setting used to be the normal method used before SLP - because temperature readings weren't available 24/7 which were needed to make reasonable guesses for the SLP reduction. So, the altimeter setting has no temperature dependence, but again uses a fancy math formula to try and guess what the air pressure measurement would be if we could move the site down to sea level elevation. It is generally thought that the SLP measurement is a better way to do this adjustment than the altimeter setting method - but not all agree.


What are you doing?
I'm interested in which method my fellow Weather Catters are reporting? Do you adjust for altitude or not?
Blick


Steve

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Re: AWEKAS
« Reply #5 on: August 21, 2017, 05:24:29 PM »
I am only at 686 feet, so there's likely not much difference between the two.

When I set up my station, I entered elevation, and then carefully adjusted the barometric pressure so that it read the average of the two airports within 20 miles of my station. I've checked this over the years and it has still been close to the average, and I usually have 98-100% rating on BP on CWOP.

I am assuming that the local airport's barometric pressure reading is at elevation, because the METAR contains "sea level pressure not available" for one of the airports. The other, Cleveland Hopkins, shows both on its METAR. Converting the listed seal level millibars to in/hg yields only .02" difference than their posted pressure.

So I'm good either way.
Steve - Avon, Ohio, USA


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elagache

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Confused round #2 (Re: AWEKAS)
« Reply #6 on: August 21, 2017, 10:43:37 PM »
Dear Blick, TechnoMonkey, and WeatherCat troubleshooters,

Just talked to Davis tech support. If you enter your elevation in the Davis setup screen, the pressure is adjusted for altitude and gives you the "altimeter setting" reading. If you do not enter an elevation, the pressure is not adjusted for altitude and gives you the "sea level" reading. According to Davis, both methods are used and you pick the one you want.

But wait a minute, that just doesn't make any sense.  ??? Without the elevation the station cannot make any correction - how could it?  So this has to be reversed.  If you don't put in the elevation, then it reports the raw pressure that the sensor reports - whatever your elevation.  If you provide the elevation, the console can then compute the weight of the column of air that would exist where the pressure you are reporting at your elevation, would be at sea level.  It then adjusts the pressure for that additional weight of air.  That has to be how it works.

Personally, I have entered the elevation so my station should be reporting the pressure as if I was at sea level.

Cheers, Edouard

xairbusdriver

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Re: AWEKAS
« Reply #7 on: August 23, 2017, 08:04:35 PM »
This table might help check the accuracy of the Pressure reading you are seeing. It might also be interesting to look at the text below the table to see the variables used in the computations.

elagache

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Thanks for the USSA reference. (Re: AWEKAS)
« Reply #8 on: August 23, 2017, 11:16:57 PM »
Dear X-Air and WeatherCat users who can still remember some of their college course contents,

This table might help check the accuracy of the Pressure reading you are seeing. It might also be interesting to look at the text below the table to see the variables used in the computations.

Thanks for the reference.  I found this Wikipedia article referenced at the bottom interesting:

https://en.wikipedia.org/wiki/U.S._Standard_Atmosphere

I remember just enough about ideal gas models to realized that this is . . . . . a little bit too simplistic!  ;D

Cheers, Edouard  [cheers1]

Blicj11

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Re: AWEKAS
« Reply #9 on: August 26, 2017, 02:38:18 AM »
Just got off the phone with Davis Technical Support, Round 2.

Summary:
Davis has its own formula for correcting barometric pressure for altitude. It is not the same formula used by NOAA, but it is much less complicated and provides almost the same result (within .03%). The Davis formula uses temperature as a variable whilst NOAA does not. The Davis formula does not produce an official "altimeter reading" due to the differences in its formula from the official NOAA formula. More information is available here, scroll down to the Barometric Pressure section: http://www.davisnet.com/product_documents/weather/app_notes/AN_28-derived-weather-variables.pdf

Two methods to adjust:
Davis says there are two ways to adjust pressure for altitude.
  • Enter your altitude in the console setup screen; the Davis formula will be used to calculate pressure adjusted for your altitude
  • Leave the console altitude setting blank, then manually calibrate your pressure to match the closest airport or other pressure reading you trust
If you do not want your pressure adjusted for altitude, leave the elevation setting blank and do not calibrate the console pressure.

WeatherCat
I still don't know if WeatherCat does anything with barometric pressure other than capture it straight off the console. Altitude is a setting we enter in WC, but I don't know that it used in any calculation. If you want to use Method 2 above as your altitude correction method, you can, of course, calibrate the barometric pressure either in the Davis console or in WeatherCat.

AWEKAS
AWEKAS apparently wants the raw pressure reading, not adjusted for altitude. Since no other weather service wants the pressure reported this way, unless WeatherCat has some way to do an unadjusted pressure calculation, it appears my best option is to stop reporting data to AWEKAS, so I am considering taking my toys and going home.
Blick


xairbusdriver

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Re: AWEKAS
« Reply #10 on: August 26, 2017, 04:05:06 AM »
I really don't see any other choice for you, Blick. But, in my humble opinion, it's their loss! [banghead] Sounds like AWEKAS is run by Microsoft; "Just do it our way!" [rolleyes2] At least MS didn't make it a slogan; The Apple Way! cmu:-)

I think I noticed the formula at the company I linked to last post does use altitude. But they use different lapse rates for three (I think) different altitude ranges. Not sure there is any standard formula unless The Federation left notes about it when they last visited Earth. :o

elagache

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Something is contradictory here. (Re: AWEKAS)
« Reply #11 on: August 26, 2017, 10:36:34 PM »
Dear Blick, X-Air, and WeatherCat data submission service troubleshooters,

AWEKAS
AWEKAS apparently wants the raw pressure reading, not adjusted for altitude. Since no other weather service wants the pressure reported this way, unless WeatherCat has some way to do an unadjusted pressure calculation, it appears my best option is to stop reporting data to AWEKAS, so I am considering taking my toys and going home.

I understand your frustration, but the AWEKAS reply in your original posting is extremely clear:

This morning, after sending data to AWEKAS for more than two years, I received notice from them that they had turned off my barometric pressure reading because it is not set to sea level.

In particular,  their second reply is even more direct:

The altitude of the station is uninteresting all weather stations (and airports) measure at sea level.

Please adjust your barometer reading to sea level

They are claiming that either your Davis console is incorrectly computing the data or perhaps you have accidentally have WeatherCat making some adjustments as well.  If I were you, I would double-check that the Davis console has the correct elevation and see what WeatherCat has under its calibration screen.  Here is what mine looks like:



It is possible that the calibration data got corrupted somehow so it isn't all zeros.

You should be able to give AWEKAS data in the form they seek.

Let us know if you spot something.

Cheers, Edouard

xairbusdriver

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Re: AWEKAS
« Reply #12 on: August 27, 2017, 12:35:56 AM »
BTW, that Calibration table is in the Misc2 tab of the WC prefs, left-hand column, between the FTP/Sylvester area and the Misc Graphics Options. I'd never even looked at it before, that's probably why mine is all zeros, except for the two multipliers.

Just a reminder, your station "Elevation" asks for Meters, I'm sure one could enter feet and WC would not complain nor warn that the data generated might be off a bit!

Additionally, it's been so long since I entered my info, I'm wondering if I actually used the "Set Details" button...  [banghead] [rolleyes2]

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Re: AWEKAS
« Reply #13 on: August 27, 2017, 06:24:41 PM »
AWEKAS
AWEKAS apparently wants the raw pressure reading, not adjusted for altitude. Since no other weather service wants the pressure reported this way, unless WeatherCat has some way to do an unadjusted pressure calculation, it appears my best option is to stop reporting data to AWEKAS, so I am considering taking my toys and going home.

Hi Blick, all,

Something does not add up... :)
AWEKAS wants a pressure reading which can be compared to values from other weather-stations. Since they are all located on a different altitude, the 'reference' altitude used is sea level. So if you set your altitude on your VP Console, Davis will compensate and show the air pressure as if you were at sea level. This way AWEKAS can 'connect the dots' an determine where the high and low pressure systems are. I'm pretty sure WC will simply read this 'corrected' value straight from the console.

I just checked the AWEKAS site and I see weather-stations in Switzerland at 2,800m (±9,100 ft) reporting 1014hPa. A nearby station at 215m (700ft) is reporting practically the same value so they MUST be using the same reference altitude (= sea level).

Jos

Blicj11

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Re: AWEKAS
« Reply #14 on: August 28, 2017, 05:43:01 AM »
Bedankt Jos:
What you say makes absolute sense to me. They are asking me to adjust for sea level when I am already doing so. I will try once more to clarify with them.

Edouard:
All good suggestions Edouard, but I had already checked both the hardware and software calibrations and all are as they should be. I have no "extra" calibration in either the console or WeatherCat and the elevation is correct in both. In addition, when I compare my pressure readings to the SLC Airport, I am pretty much where I should be given the altitude difference between here and there and I know they adjust for sea level.
Blick