[Met_help] point_stat

John Halley Gotway johnhg at rap.ucar.edu
Tue Apr 28 11:39:57 MDT 2009


Thanks for sending the data.  I see what the problem is - there's a bug in the library code that reads the valid time of the GRIB forecast file.  It thinks it 2098 as opposed to 1998.  So Point-Stat
is looking for observation values that are in the time window 20980430 +/- 5400 seconds.  And of course, it doesn't find any!

I'm headed out for the day, but I'll put together a fix and send it to you tomorrow.

In the meantime, try using the "-valid_beg" and "-valid_end" command line options to manually set the matching time window.  That should get you non-zero matched pairs.

Thanks for finding this issue!


Mark Seefeldt wrote:
> John,
> Thank you for all of the tips and suggestions which you have provided. I
> have worked through the different items and I am still not getting
> matched pairs when I should be.
> I have uploaded the following files to the anonymous ftp:
>   phy_sheba-barrow-d01-199805.nc - nc observation file
>   phy_sheba-barrow-d01-199805.txt - text observation file
>   wppout_d01_1998-04-30_00.grb - GRIB output from using WPPv3.1
>   PointStatConfig-phy_sheba - point_stat configuration file
> The WRF simulation is for an entire month, centered over Alaska.  The
> observations are surface pressure, temperature, relative humidity,
> downwelling shortwave, and downwelling longwave radiation for a single
> site, Barrow, Alaska.
> Let me know if you have any additional questions.
> Thanks
> Mark
> John Halley Gotway wrote:
>> Mark,
>> Let me make a few comments about this.
>> First, depending on how you configure Point-Stat, getting 0 matched
>> pairs for certain combinations of variables/message type may be fine.
>> For example, if you configure Point-Stat to verify Temperature at
>> 2-meters above the surface (TMP/Z2) and at 500mb (TMP/P500) using
>> message types of ADPSFC (surface obs) and APDUPA (upper air obs), you
>> would actually expect to get 0 matched pairs for TMP/Z2 vs APDUPA and
>> 0 matched pairs for TMP/P500 vs ADPSFC.  So sometimes having 0
>> matched pairs is fine.
>> However, if you're getting 0 matched pairs when you expect that you
>> should actually be finding some, here's what I'd ask myself:
>> - Am I applying some masking region (a grid or a polyline) that is
>> perhaps not working like I expect?  Try rerunning with the masking
>> grid set to FULL to verify over the whole domain.
>> - Does my forecast field contain valid data?  Clearly Point-Stat is
>> finding the fields you'd like to verify, otherwise it'd error out.
>> But if what it's finding contains only bad data, it won't find any
>> matched pairs.  Can you view the forecast field with some other tool
>> to check that the field contains valid data?  For NetCDF format, use
>> ncview.  For GRIB, "wgrib -V" will tell you the min/max data values.
>> Or you could view the GRIB file using NCL or IDV.  Or you could run
>> it through the MET-MODE tool and look at the output plot.
>> - Do I have my valid times correct?  Am I using observations that are
>> valid around the same time that my forecast file is valid?  In the
>> Point-Stat config file, you could set the "beg_ds" and "end_ds" values
>> to define a VERY large time window to see if you can get some
>> matched pairs.
>> - Lastly, do the observations I'm using not match my forecast for
>> some other reason?  For example, are the message types for the
>> observations correct?  You could try doing an ncdump to see what
>> message types are in your point observation file (ncdump -v hdr_typ
>> file_name.nc | sort -u).  Or are the observations not matching for
>> some other reason?  This would be the most difficult to determine!
>> Hopefully that'll help you figure out what's going on with your data.
>> I'd suggest "opening" things up as much as possible (mask grid = FULL
>> and set beg_ds/end_ds very large) to try to get non-zero matched
>> pairs, and go from there.
>> If you're still having problems after trying these things, feel free
>> to send me some sample files, and I could take a look to see what
>> going on.  You'd need to send me: (1) Forecast file input for
>> Point-Stat. (2) Observation file input for Point-Stat. (3)
>> Configuration file input for Point-Stat. And you could post those
>> files to RAL's anonymous ftp site: ftp ftp.rap.ucar.edu username =
>> anonymous password = "your email address" cd incoming/irap/johnhg put
>> "those 3 files" bye (to exit ftp)
>> Thanks and good luck, John
>> Mark Seefeldt wrote:
>>> I am working on a model evaluation using point_stat in MET.  As it
>>>  processes I am getting 0 pairs matched, therefore no statistics.
>>> Is there a preferred method to identify if it is the observation
>>> file, the forecast file, or the configuration file where the error
>>> resides resulting in the lack of matched obs/fcst values?  I am at
>>> a loss as to what is wrong in my setup which is preventing the
>>> obs/fcst pairs to be matched and to create the output.
>>> Thanks
>>> Mark _______________________________________________ Met_help
>>> mailing list Met_help at mailman.ucar.edu
>>> http://mailman.ucar.edu/mailman/listinfo/met_help

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