Author Topic: What do the numebrs mean?  (Read 8266 times)

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Offline MesquiteWx

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What do the numebrs mean?
« on: March 09, 2008, 12:52:56 AM »
I have had my new Davis VP2 set up almost two weeks. It will be 2 weeks on Tuesday. Now my first check was when I had my LaCrosse and it got horrible checks and I am still seeing some hang over from that old station. Also I had a station down the street from me that had software issues so it was sending wrong data. It is slowly getting better though and the other station is working again. So now that I can get accurately checked I would like to know what the numbers mean and what I am suppose to be looking at.

http://weather.gladstonefamily.net/site/C9936

So what does these numbers mean for this,

Average barometer error:    
Error standard deviation:    
Worst daily average barometer error:    
Worst daily standard deviation:    

What am I suppose to be looking at?

-Thanks


blackjack52

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Re: What do the numebrs mean?
« Reply #1 on: March 09, 2008, 01:51:38 AM »
quoteBy default, the longer analysis periods display graphs that show the long term performance of this station. The graphs show the mean error over time, and include error bars which are one standard deviation long. This provides an easy way to see if there are any underlying trends in the data. Note that a 'step' in your data does not (necessarily) mean that something happened to your station. It could mean that another station came online in the local area, and they are changing the analysis.

If the error above is POSITIVE, then it means that the analysis temperature is HIGHER than the reported temperature. This means that your sensor is reading COLDER than expected.You can look at those for comparison purposes. The average difference between your station and each station below is listed as well. This may allow you to detect local stations which are erroneous. You can also use these numbers to adjust your instruments -- especially if a number of ASOS stations have similar differences to your station. Also, try increasing the analysis period to more than the default 28 days. The difference is only given if both stations report reasonably often during each day. Some stations only report every 6 hours, and this makes the average of less interest. In this case, the average is not displayed.


Your temps are failng.


« Last Edit: March 09, 2008, 01:58:56 AM by MadALwx »

Offline MesquiteWx

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Re: What do the numebrs mean?
« Reply #2 on: March 09, 2008, 10:55:17 AM »
I am not referring to the graphs, I am talking about the numbers below that. What exactly am I suppose to be looking at? What is my station and what is the others.

24 hours     Day time     Night time
Average temperature error   -2.2 F   -2.9 F   -1.8 F
Error standard deviation   1.3 F   1.3 F   1.0 F
Worst average temperature error   -2.7 F   -3.7 F   -2.4 F
Worst standard deviation   1.4 F   1.6 F   1.8 F

Is the average temperature error for my station or overall in my area? Worst average, Worst Standard etc what do those numbers mean and what should i be looking at and comparing. Most of what you listed I have read before from the Madis page but it doesn't help much If I do not know what I am looking at. It says "If the error above is POSITIVE, then it means that the analysis temperature is HIGHER than the reported temperature. This means that your sensor is reading COLDER than expected." Which error am I looking at "Error standard deviation"? If that is the case then I am 1.3 off then those in my area which is about right from what I have been noticing. So since that error if that is what I am looking at is positive that means it is running colder correct?

I don't think the temperature is failing. Like I mention in my first post. A lot of that I think is hang over from my old station and their is just not enough data yet to correctly process yet. If you look at the 28 days and the 3-7 days the errors below the temperatures are different. I get green thumbs up on all of them and 2 checks for Barometer and Dew Point/ Relative Humidity. I know the person 1.7 miles from me uses a Daytime FARS and most of the time my temp readings are 1+/- off from his. I am not real concerned about QC checks all that much especially with the numbers being that close and you have to take into consideration of Micro Climates. I just would like to know what the numbers above mean and what I am looking at and suppose to be looking at so I can detect a problem in the furture should one arise.

Here is the 7 day data. Compare it to the 28 day and you will see what I am talking about. The numbers are more within range which is why I think it is Hang over form the old station which were sending these errors to start with. Would this be a correct assessment? I think once I get some more time under this new station things should level out.

http://weather.gladstonefamily.net/site/C9936?tile=10;days=7#Data


Offline jmcmurry

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Re: What do the numebrs mean?
« Reply #3 on: March 09, 2008, 11:12:38 AM »
Those numbers are your station in comparison with a group of others around you, but not necessarily the ones listed at the bottom of the page.  There is no way that I've found to know which stations are actually used in the computation.  Apparently a closely held MADIS secret.  My guess though is that they're probably in the equation.

When you look at the longer time periods yes, your old station readings will have an effect and that will diminish with time.  I like to look at a short period like 3 days because I figure I'll notice problems quicker that way.

As for standard deviation, you can google that just like I did and it probably still won't mean much to you.  It's something for statisticians that completely goes over my head.

- Jim

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Offline MesquiteWx

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Re: What do the numebrs mean?
« Reply #4 on: March 09, 2008, 11:25:18 AM »
Those numbers are your station in comparison with a group of others around you, but not necessarily the ones listed at the bottom of the page.

Thanks, I had heard they compare them to others around you. Do you know which numbers are your station and which are the group they are comparing them to are all of them your station? Which ones should I be more concerned with and be comparing.

I know this guys software has been messed up. He use to pass everything and he is the closest station to me, but has you stated that probably means nothing. His numbers are way off the chart compared to mine when it comes to temps. The more I look at things I should be looking at the Average temperature error correct? The rest is just stats right

http://weather.gladstonefamily.net/site/C6153


blackjack52

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Re: What do the numebrs mean?
« Reply #5 on: March 09, 2008, 11:26:26 AM »
If the error above is POSITIVE, then it means that the analysis temperature is HIGHER than the reported temperature. This means that your sensor is reading COLDER than expected.You can look at those for comparison purposes. The average difference between your station and each station below is listed as well. This may allow you to detect local stations which are erroneous. You can also use these numbers to adjust your instruments -- especially if a number of ASOS stations have similar differences to your station.

Offline MesquiteWx

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Re: What do the numebrs mean?
« Reply #6 on: March 09, 2008, 12:28:01 PM »
If the error above is POSITIVE, then it means that the analysis temperature is HIGHER than the reported temperature. This means that your sensor is reading COLDER than expected.

I understand and know that. I had read that on my QC page. That means nothing to me though if I am not sure of which set of numbers I should be paying attention to. So what I am asking is which numbers should I be focusing on and which of those numbers is what.

So for example on my 7 day here are the numbers. Which of these should I be paying attention to. which is my station?

 24 hours     Day time     Night time
Average temperature error   -2.2 F   -2.9 F   -1.8 F
Error standard deviation   1.3 F   1.3 F   1.0 F
Worst average temperature error   -2.7 F   -3.7 F   -2.4 F
Worst standard deviation   1.4 F   1.6 F   1.8 F

I have 4 sets of numbers above and do not know what is what and what I am looking at or should be paying attention to. I know it is comparing it to other stations but which is mine and which are the numbers are those it is comparing it to? Their are positive and negative numbers. So unless I know what I am looking at I am not sure what it is doing.


Offline capeweather

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Re: What do the numebrs mean?
« Reply #7 on: March 09, 2008, 01:12:15 PM »
You may want to contact Russ at CWOP and ask him. He may be able to help you and give you the detailed info you are looking for.

Chris
Cape Coral, Florida
Website: http://www.capeweather.com
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Offline MesquiteWx

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Re: What do the numebrs mean?
« Reply #8 on: March 09, 2008, 10:51:30 PM »
I have emailed him over a week ago and I haven't received a response yet. I am just trying to find out with those four sets of numbers which one I am suppose to be more focused on that is my station? Anyone know?

Offline Bob65

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Re: What do the numebrs mean?
« Reply #9 on: March 10, 2008, 07:38:51 AM »
Hi,
I've asked the same question on two forum with no answer that I can understand. Googling for "standard deviation" really confused me so I'm hoping for a clear understandable ( to me ) answer somewhere.
I have looked at the WXQC mailing list but did not register and post the question there, but I think that may be a good place to try.
Good luck with this question. If you find something, please post it here.
Regards, Bob
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jwyman

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Re: What do the numebrs mean?
« Reply #10 on: March 10, 2008, 08:17:33 AM »
MesquiteXmas,
   Average temperature error   -2.2 F   -2.9 F   -1.8 F
   Error standard deviation   1.3 F   1.3 F   1.0 F
  Worst average temperature error   -2.7 F   -3.7 F   -2.4 F
  Worst standard deviation   1.4 F   1.6 F   1.8 F

You want to be looking at the average temp error.  The Error Standard Deviation is the "spread" of the data based on the mean temp error. The smaller the error SD, then the closer the spread, and vice versa..
When it comes to the barometer, I look at the Avg. Barometer Error. That's what I use to adjust to "good" stations around me. I tend to use airport metars which usually have better equipped stations than your average joe.

Hope that helps.....

Jim
« Last Edit: March 10, 2008, 08:38:02 AM by jwyman »

Offline Bob65

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Re: What do the numebrs mean?
« Reply #11 on: March 10, 2008, 12:35:12 PM »
Hi,

MesquiteXmas,
   Average temperature error   -2.2 F   -2.9 F   -1.8 F
   Error standard deviation   1.3 F   1.3 F   1.0 F
  Worst average temperature error   -2.7 F   -3.7 F   -2.4 F
  Worst standard deviation   1.4 F   1.6 F   1.8 F

You want to be looking at the average temp error.  The Error Standard Deviation is the "spread" of the data based on the mean temp error. The smaller the error SD, then the closer the spread, and vice versa..

Hope that helps.....

Jim


If I understand this, the math would be all temperatures submitted  added together and divided by the number submittal equals the average mean temperature for the 24 hours. This is also done for day and night temps. Now the next part,  "error Standard Deviation is the "spread" of the data based on the mean temp error", would be the difference between the actual average (mean) temperature and the temperature that CWOP/Madis thinks it should be.
If I have this right, and I believe the error to be correct and I made a tweak of -1.3 degrees in my reports then my average 24 hour error would be zero.
Do I have this right?
Regards, Bob
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jwyman

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Re: What do the numebrs mean?
« Reply #12 on: March 10, 2008, 12:45:41 PM »
Bob,
  The Avg Temp Error is the number you look at to see how far off from the other stations you are.  This is the so-called differeance between you and CWOP/MADIS. The deviation number just shows the spread around the mean number your data points ar scattered. If the number is small, then your data points are closed together and are fairly consistent. If the number is large, then your data points vary over a large range meaning possible hotter than hot and colder than cold readings....

Jim

Offline Anole

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Re: What do the numebrs mean?
« Reply #13 on: March 10, 2008, 01:06:29 PM »
Hi,
I've asked the same question on two forum with no answer that I can understand. Googling for "standard deviation" really confused me so I'm hoping for a clear understandable ( to me ) answer somewhere.
I have looked at the WXQC mailing list but did not register and post the question there, but I think that may be a good place to try.
Good luck with this question. If you find something, please post it here.
Regards, Bob

In it's most simplistic meaning, standard deviation measures the spread (the difference between the high and low) of values within a data set. The greater the standard devation, the wider the range of values in the data set.

I say simplistic because the implication is that you figure it out by subtracting the lowest value from the highest but it doesn't quite work that way. Because the values in a data set may not be uniformly dispersed (ie most may be bunched up near the low while only a few are near the high as an example) figuring it out that way wouldn't be truly representative of the spead of the values. So to compensate and give a better representation of the values a slightly more invovled (but still very simple) calculation is made.

In it's more formal mathematical definition, standard deviation is the root mean square deviation of a set of values from their mean value. You figure out a weighted average deviation (the root mean square deviation) and compare it to the raw average.
To figure it out:
1) first find the mean (average) of the values in the set.
2) Then calculate the deviation for each value from that mean. In other words, subtract then mean you figured out in the first step from the raw value.
3) Square each of the deviations from step 2.
4) Get them mean (average) of the values from step 3.
5) Take the square root of that mean and you have your standard deviation.

At least I think that's right, it's been a long, long time since I took statistical analysis and I didn't like it even back then. ;)

jwyman

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Re: What do the numebrs mean?
« Reply #14 on: March 10, 2008, 01:16:53 PM »
Bingo!   =D> =D>  Give that man a lollipop! :-P :-P :-P :-P

Jim

blackjack52

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Re: What do the numebrs mean?
« Reply #15 on: March 10, 2008, 03:55:16 PM »
Due to microclimates the only thing that you really need to worry about is getting one or two thumbs up.  The average error will tell you which way your calibrations need to be in order to start getting one or two thumbs up.

Simply looking at the graphs and reading that paragraph above each graph will show which way you need to calibrate to get back within the standard deviation. 
« Last Edit: March 10, 2008, 04:03:47 PM by MadALwx »

Offline Cienega32

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Re: What do the numebrs mean?
« Reply #16 on: March 11, 2008, 12:55:31 AM »
Bob,
  The Avg Temp Error is the number you look at to see how far off from the other stations you are.  This is the so-called differeance between you and CWOP/MADIS. The deviation number just shows the spread around the mean number your data points ar scattered. If the number is small, then your data points are closed together and are fairly consistent. If the number is large, then your data points vary over a large range meaning possible hotter than hot and colder than cold readings....

Jim
So if one had a station that was absolutely accurate in the midst of erroneous stations then the 'good one' would get the red X?

Pat ~ Davis VP2 6153-Weatherlink-Weather Display-StartWatch-VirtualVP-Win7 Pro-64bit
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jwyman

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Re: What do the numebrs mean?
« Reply #17 on: March 11, 2008, 07:27:21 AM »
Very Possible... That's when I look at the ariport data first because they SHOULD have better equipment and more accurate readings. You can check to see how far off you are from those readings. Easier to do with barometric readings than temp and humidity due to microclimates...

Jim

Offline Bob65

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Re: What do the numebrs mean?
« Reply #18 on: March 11, 2008, 08:05:24 AM »
This has been a very informative thread and I thank all for sharing.
In trying in make sure that my data is accurate as possible I try to learn and this is a great place to do that.
I found it much easier to check temperature , rain and air pressure than relative humidity because the first 3 can be checked with inexpensive things that I have but Rh is much more localized and difficult to verify without more costly equipment like a sling or electronic hydrometer. Unfortunately I do not have an airport close by but have had two new pws go online within 2 miles of me.
I remember now why I dislike statistical analysis. I thought back when that when numbers get averaged and squared they lose any practical value and still feel the same ( except maybe for political purposes :-P )
Thanks again.
Regards, Bob
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blackjack52

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Re: What do the numebrs mean?
« Reply #19 on: March 11, 2008, 09:27:03 AM »
So if one had a station that was absolutely accurate in the midst of erroneous stations then the 'good one' would get the red X?

I say this is highly likely as to why readings bounce around within the standard deviation.  Due to new stations coming online my barometer will be dead on birdies for days, then suddenly it is bordering going outside the box.  Davis instrumentation is very accurate provided it is sited correctly, so I just let it be, then it starts swinging back to the center after a few days.
« Last Edit: March 11, 2008, 09:41:35 AM by MadALwx »

blackjack52

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Re: What do the numebrs mean?
« Reply #20 on: March 11, 2008, 04:20:54 PM »
I'm sure this holds true for everyone that answered; I'm just really glad that we all chipped in to help out! 


You're welcome.

 

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