[IDV #ZEC-697467]: METAR decoding problem in the IDV

Hi Steve-

In the latest nightly build, I've added in a CA (cloud amount) variable for the 
METARs that computes a synthetic cloud coverage from the CC1, CC2 and CIGC 
variables.  I've removed CC1 and CC2 as aliases for cloud cover to avoid 
confusion.  While this is not perfect (e.g. obscurred (X) information is lost 
in the decoding), it does provide a more reasonable estimate of the WMO cloud 
coverage value.

Don Murray

> > Full Name: Steve Nesbitt
> > Email Address: address@hidden
> > Organization: Department of Atmospheric Sciences, University of Illinois
> > Package Version: 2.8 build date:2010-01-15 20:48 UTC
> > Operating System: Mac OS X
> > Hardware: Java: home: 
> > /System/Library/Frameworks/JavaVM.framework/Versions/1.6.0/Home version: 
> > 1.6.0_17 j3d:1.3.1
> > Description of problem: Hello,
> >
> > I am having students make surface maps from METAR data in IDV.  We are 
> > noticing that cloud cover (fields CC1 and CC2) are often missing in the 
> > data even though cloud cover is being reported in the raw METAR reports.  I 
> > have attached an example screen capture showing that little cloud cover is 
> > being plotted (only a few stations), and the plot for Champaign showing CC1 
> > and CC2 are missing. Note the associated raw METAR report below, which 
> > indeed reports a cloud cover of OVC.  This issue precludes making complete 
> > surface maps in IDV.
> >
> > KCMI 211753Z 06016KT 2SM -RA BR OVC005 01/M01 A2964 RMK AO2 SFC VIS 2 1/2 
> > UPB37E39RAB39 CIG 003V008 SLP045 P0001 60001 T00061006 10011 20000 58022
> 
> The CC1, CC2 and CIG values in the METAR datasets are not the WMO cloud 
> coverage values one might think.  They are McIDAS representations of the 
> ceiling, and other cloud levels.  The values range from 0-3 for CLR, SCT, 
> BKN, OVC and 5 for FEW.  In this case, there is only one level and it is a 
> ceiling, so the CIGC is 3 and the others are missing.  For the example:
> 
> KHSP 261440Z AUTO 25013G23KT 10SM SCT018 BKN047 OVC065 M04/M06
> A2966 RMK AO2=
> 
> we have:
> 
> Date                            ID      CC1     ZCL1    CC2     ZCL2    CIGC  
>   CIGH
> Tue, Jan 26 2010 14:00 GMT    KHSP    1       1800    3       6500    2       
> 4700
> 
> 
> So, the ceiling is the BKN (2) layer, the SCT (1)layer is CC1, and the other 
> non-ceiling cloud group (CC2) is the OVC (3) layer.
> 
> The synoptic and ship reports have a CA group which is the WMO cloud coverage 
> value.  We are going to look at fabricating a CA group for the METARs based 
> on CC1, CC2 and CIGC.  The problem is that some information has been lost 
> (like thin layers), so the mapping might not be exact, but at least would be 
> better.
> 
> Hope that explanation helps.
> 
> Don
> 
> 
> 
> 


Ticket Details
===================
Ticket ID: ZEC-697467
Department: Support IDV
Priority: Normal
Status: Open