[Met_help] point_stat

John Halley Gotway johnhg at rap.ucar.edu
Thu Apr 30 07:29:07 MDT 2009


Glad it's working now.  I did notice how your observations were laid out and was wondering what type of verification you were trying to do.

Basically, you'd like to collect matched forecast/observation pairs at a single location through time, and then compute statistics on that set of matched pairs.  Unfortunately, MET isn't set up to
handle that type of task well.  You can use MET to do it, but at this point, it's a bit more cumbersome than I'd like.

Point-Stat is designed to compare a forecast field to a set of observations at a SINGLE point in time.  Point-Stat able to aggregate matched pairs in space but not in time, as you'd like.
Unfortunately, 'cat'ing together all of your forecast files does not have the desired effect.  Since the output of WPP is one file for each valid time, that's the type of data that MET expects.  When
you specify the forecast field as "PRES/Z0" in the configuration file, Point-Stat looks in the input forecast file for a matching record.  It uses the first one it finds, so it'd only use the data for
the first valid time in your file and ignore the rest of the records.

Here's how you'd need to do this:
(1) Do NOT cat together your forecast GRIB files - keep them separate.  But all your observation points can be in the same file.
(2) Create a masking station id file that lists the stations you'd like to verify (just "Barro", I suppose).
(3) In the Point-Stat config file, set the following:

   - Set "mask_sid" variable to point to that station id file.
   - Set "beg_ds" and "end_ds" to define a matching time window around each forecast valid time.  This should be set carefully so that you get exactly one matched pair for Barro for each run.  You
don't want to accidentally include the one from the day before or the day after.
   - Set the output_flag as follows to dump out only the matched pair data:
       output_flag[] = [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 ];
   - Set interp_method[] = [ "UW_MEAN" ]; for unweighted mean.
   - Set interp_width[] = [ 1 ]; to only use the nearest neighbor.
   - You may want to consider using additional interpolation methods and widths.  That way you could see how the results change by smoothing over larger areas.

(4) For each forecast valid time, run Point-Stat once.  You need to pass it the forecast file for that time and the point observation file.
(5) Now you've run Point-Stat about 30 times and have generated about 30 STAT files - each only containing one MPR line (or multiple if you use multiple interpolation methods).  To aggregate through
time, you can run the STAT-Analysis tool, passing to it the directory containing those 30 STAT files "-lookin stat_dir".  You'll want to run the "-job aggregate_stat" job with "-line_type MPR".  And
you can select the type of stats you want computed by setting the "-out_line_type" argument.  If you've using multiple interpolation methods, you can use the "-interp_mthd" and "-interp_pnts"
arguments to specify which matched pairs should go into the calculations.

So that'd be the way to do it.  Sorry it's so cumbersome.  We do realize that it'd be nice to perform this type of verification more directly in a single step.  We're considering how best to support
this type of verification through time.


Mark Seefeldt wrote:
> John,
> Thank you for posting the fix so quickly.  I have retrieved the set of
> patches and have recompiled MET.  I am now getting matched pairs.
> I appear to still be struggling in producing the output which I desire.
>  I am guessing this is more of a user problem.  I'd like to step you
> through what I am trying to do and see if you have any tips to improve
> what I am doing.
> I have a month-long simulation from WRF.  The simulation runs for one
> month plus one-day, starting the last day of the previous month.  I have
> created GRIB files using WPP from the wrfout files.  The GRIB files were
> created in the three-hour intervals of the history file.  I have cat'ed
> the GRIB files together making a single file which represents the entire
> month long simulation.  That GRIB file is:  wppout_d01_1998-04-30_00.grb
> I have one month of observations for a given observation location.  In
> this case the Barrow Baseline Surface Radiation Network (BSRN)
> observations for May 1998.  From the original observation file I have a
> program which creates a text file of the observations.  That text file
> is then processed by ascii2nc to create the netcdf input file for
> point_stat.  The netcdf file is:  phy_sheba-barrow-d01-199805.nc
> The end desired result is a list of the continuous statistics for the
> entire month between the WRF model simulations for the nearest point to
> the Barrow observations in comparison to the actual Barrow observations.
>  There would be a maximum of 744 observation/forecast pairs (31 days x
> 24 hours).  This represents a maximum and not the expected because there
> are some missing values.
> When I initially ran point_stat I only got 2 matching pairs.  I added
> the command-line options -valid_beg 19980501_00 and -valid_end
> 19980531_23.  I then got 743, 741, 703, 731, and 736 matching pairs,
> depending on the variable of interest (i.e. T_2m).  That is what I would
> expect.
> When looking at the CNT file things became a little more suspect.
> -I initially noticed the following:
>   FCST_VALID_BEG : 19980501_000000
>   FCST_VALID_END : 19980501_000000
>   OBS_VALID_BEG : 19980501_000000
>   OBS_VALID_END : 19980531_230000
> The OBS fields are what I would expect.  I would expect FCST_END to be
> 19980531_2300.
> -I also noticed that I do not have FSTDEV, FSTDEV_NCL, FSTDEV_NCU,
> FSTDEV_BCL, and FSTDEV_BCU values (all are listed as NA).  I am
> wondering if it is only using the forecast value for 19980501_0000,
> therefore it cannot calculate a FSTDEV.
> My questions lie in:
> -Is what I am trying to do reasonable?
> -Is the methodology which I am doing correct?
> -Why does the FCST_VALID_END not go to the end of the month?
> -Why do I not have FSTDEV values?
> Thanks
> Mark
> John Halley Gotway wrote:
>> Mark,
>> I posted a fix for this issue.  Please retrieve the fix from the MET
>> Known Issues page:
>> http://www.dtcenter.org/met/users/support/known_issues/METv2.0/index.php
>> I'd suggest following the instructions in the "All Recommended
>> Updates" section.  There are now two bug fixes available and some
>> minor updates to the user's guide, and doing it this way, you'll grab
>> all of the updates.
>> Feel free to write with any more questions or problems.
>> Thanks,
>> John
>> Mark Seefeldt wrote:
>>> John,
>>> Thanks for the update.  Please pass around the fix when you have it
>>> completed.  The information you provided is valuable as it means that
>>> I can start processing the GRIB files for the complete evaluation.
>>> Mark
>>> John Halley Gotway wrote:
>>>> Mark,
>>>> 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!
>>>> John
>>>> 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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