[gembud] Possible bug in ensemble functionality with precipitation

Greetings.  We believe we may have found a bug when using the cumulative 
precipitation functionality with ensemble functions in GEMPAK gridded 
programs.

We are wondering if this is a known bug and if not wanted to bring it to 
the user communities attention.  Any thoughts welcome.  Details below.

Pete

Reference the Attached Images
Values plotted are scaled ("scale=2") QPF from the 03Z SREF Dec 10 2012 
run using gdplot3 for "gdfile = {sref | 03}" 

1. 2012121003f24_sref_p03i_ens_ssum.gif
Sum of all 21 members 3h QPF predictions at f24 using 
"gdpfun=ens_ssum(p03i)".  Note the values of "339" in near Philadelphia 
and "5" near Cincinnati. 

2. 2012121003f27_sref_p03i_ens_ssum.gif
Same as #1, but for f27.  Note the values of "171" in near Philadelphia 
and "2" near Cincinnati

3. 2012121003f27_sref_p06i_ens_ssum.gif
One would expect a 6hr total of 510 at Phili and 7 at Cinci.  However 
using "gdpfun=ens_ssum(p06i)" at f27 yields negative values in Cinci (but 
expected values at Phili).

Our concern is that with light precipitation events (especially if 
converted via precip type - say like freezing rain) the functionality as 
invoked above will yield erroneous results.

Additional Findings and Information
Using GEMPAK 6.4.0 on x64 system running RHEL 6.2
Confirmed error also occurs with GEMPAK 6.2.0 gempak gridded programs
Confirmed error occurs for either a p06i or p06m 
Confirmed error occurs for any given SREF run
Confirmed each member being referenced by the ensemble function "ens_ssum" 
has valid data at each grid point
Confirmed error does NOT occur when applied to single members (models). 
Example - no such error occurs when "GDFILE = nam | 12" and "gdpfun = 
p06i" for any given fhr)
All members were pulled in from NOMADS and processed using NAGRIB2
By the way we were using the "ens_ssum" to verify the wierdo results we 
found using ens_savg -- which is how we found this bug




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Attachment: 2012121003f24_sref_p03i_ens_ssum.gif
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Attachment: 2012121003f27_sref_p03i_ens_ssum.gif
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Attachment: 2012121003f27_sref_p06i_ens_ssum.gif
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