[Met_help] Problem with MET and accumulation intervals

John Halley Gotway johnhg at ucar.edu
Tue Nov 17 07:46:36 MST 2009


I knew I was forgetting something :)

Sorry about that.  Here they are.


Thomas Schwitalla wrote:
> John,
> John Halley Gotway schrieb:
>> Thomas,
>> The flags in your GRIB file are set in a way that we've never
>> encountered for precipitation.  Where did you get this GRIB file?
>> I was able to reproduce the error message you're seeing.  I stepped
>> through the call to PCP-Combine using a debugger and found that
>> unexpected flag value in the Product Description Section (PDS) of
>> the GRIB file.  I ran the file you sent and a sample GRIB file that's
>> distributed with MET through the "wgrib" utility to dump out info
>> about each record:
>> File you sent...   
>> 4:26640:d=07080100:APCP:kpds5=61:kpds6=1:kpds7=0:TR=0:P1=4:P2=0:TimeU=13:sfc:1hr
>> fcst:NAve=0
>> Sample GRIB file...
>> 2:31408:d=05080700:APCP:kpds5=61:kpds6=1:kpds7=0:TR=4:P1=3:P2=6:TimeU=1:sfc:3-6hr
>> acc:NAve=0
>> Looking at these, you can see that the value for the time range
>> indicator (TR) is set to 0 in yours, while it's set to 4 in the other
>> file.  Now take a look at Table 5 of the GRIB spec:
>> http://www.nco.ncep.noaa.gov/pmb/docs/on388/table5.html
> thanks for opening my eyes. We used a self written program to convert
> MM5 output to GRIB format. Is seems, that during the conversion
> something went wrong. We successfully used this tool to convert MM5
> output without parameterized convection at 2km resolution, but at 18km
> parameterized convection is needed.  I assume this is a problem in our
> tool :-(
>> A value of 0 is used to simply define a valid time, while a value of 4
>> is used to define an accumulation interval between times 1 and 2 (P1
>> and P2).  MET expects that the time range indicator will be
>> set as an accumulation interval for precipitation.
>> Do you think there was an error in defining the flags for this GRIB
>> file, or do you really need to be able to read this file as is in
>> MET?  If you do need to read it in MET, you'll need to make two
>> source code changes:
>> (1) Replace the file METv2.0/lib/vx_met_util/read_grib.cc with the
>> version that's attached.
>> (2) Replace the file METv2.0/src/pcp_combine/pcp_combine.cc with the
>> version that's attached.
>> Recompile MET with a "make clean" and then rebuild MET.  Please let me
>> know the origins of this file and whether we'll need to support it
>> directly in MET.
> Is it possible, that you send me the code changes as attachment now
> (they were missing in your email) ;-) ?
>> Hope that helps,
>> John
> Thanks for opening my eyes,
> Thomas
>> Thomas Schwitalla wrote:
>>> Hi John,
>>> currently I have a problem using pcp_combine with a grib dataset for
>>> precipitation verification. I get the following error message as an
>>> example:
>>> "can't find grib code 61 with accumulation of XX hours in grib file". I
>>> attached a sample grib file, maybe you can reproduce the error.
>>> Best regards from Hohenheim
>>> Thomas
>>> ------------------------------------------------------------------------
>>> _______________________________________________
>>> Met_help mailing list
>>> Met_help at mailman.ucar.edu
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