[wxqc] MADIS explanation needed

[Merton Campbell Crockett]

On 10 Apr 2008, at 19:42:35, Philip Gladstone wrote:

> ... Also, the thumbs ratings are more heavily weighted towards  
> recent observations.


Which recent observations are used for the ratings?  Is it recent  
historical data from the specific weather observation station or does  
it involve recent historical data from all weather observation  
stations in a region?


> In a nutshell, the thumbs represent the percentage of observations  
> that pass the MADIS checks. These are quite coarse (2 mbar, 6  
> degrees F for temperature etc), but do a good job of ruling out  
> really wacky readings.
>
> The red/green classification is a tighter set of checks, but is  
> based on the average over the analysis period (normally 28 days  
> unless you clicked on one of the embedded links to change it). Thus,  
> you might get a red X for pressure if your pressure tracked the  
> analysis well, but with a constant offset, and the offset was large  
> enough (say 1.5 mbar). it could be that none of your readings fail  
> MADIS checks, but nevertheless, they are unlikely to be 'right' (for  
> some value of right).


Is the system that performs the more restrictive checks the one that  
generates the station analysis graphs?  Is this the system that  
generates the "error" reports for the weather metrics that are  
monitored?

Why does a Santa Ana weather condition appear to increase the variance  
or "error"?


> For temperature, a separate analysis is done for daytime readings  
> and nighttime readings (omitting the hour before and after sunrise  
> and sunset). This allows the system to spot problems like solar  
> heating.


The analysis graph tends to show temperature starting to rise at the  
line marked sunrise; however, this is an hour or more before the  
overnight low is reached.  Why?

I've been observing weather all my life but didn't get a weather  
station until last Christmas.  I joined CWOP in January and am trying  
to understand how to use the quality control information to ensure  
that my observation data is accurate.



Merton Campbell Crockett
m.c.crockett at roadrunner.com