[Met_help] PWAT verification with MET Tools

[John Halley Gotway]

Thomas,

OK, sorry, my mistake.  You need to use:
fcst_field[] = [ "PWAT/L0" ];

The "L0" says "give me a field with a level value of 0 and I don't care what type of level it is".  When you say "Z0" the code looks at what type of level is in the GRIB file and only uses the one
defined on vertical levels.  But PWAT isn't defined on a vertical level - it's level type is the "entire atmosphere (considered as a single layer)".

The reason why we have all these silly letters is to avoid conflicts.  For example, other users have had temperature at 2-meters and 2 mb.  Both records will have a level value of 2, but "Z2" will get
you the first one, while "P2" will get you the second one.  And if all else fails, you can always say "PWAT/R171" to explicitly give you GRIB record number 171 - which wgrib told us is the record
number for PWAT in that file.

I was able to get it to run using "PWAT/L0", but initially Point-Stat found no matched pairs.  It looks like there a slight time offset that's causing the problem.  This is a 1-hour forecast
initialized at 2007072000 - so the valid time is 2007072001.  I looked at the observations your using, and they range in time from 20070720_230700 to 20070720_235200.

You're welcome to compare this forecast to these observations if you'd like, but you'll need to set the matching time window differently to do so.  In the config file, you can set the "beg_ds" and
"end_ds" parameters to define the matching time window in reference to the forecast time window.  Alternatively, the "-valid_beg" and "-valid_end" command line options override the "beg_ds" and
"end_ds" settings in the config file.

Once I changed the time window, I was able to get matched pairs.

Hope that helps.

John

Thomas Schwitalla wrote:
> I uploaded the data on your ftp server, as one timestep is about 100MB...
> 
> Thanks again for your effort! Your reaction time is fantastic! 8-)
> 
> Thomas
> 
> John Halley Gotway schrieb:
>> Thomas,
>>
>> Please send me a sample forecast file, a sample ASCII file, and the
>> PointStatConfig file you're using.  I'll take a look and see if I can
>> figure it out.
>>
>> If the forecast file is pretty large, you could post those to our
>> anonymous ftp site:
>>
>> ftp ftp.rap.ucar.edu
>> username=anonymous
>> password="your email address"
>> cd incoming/irap/met_help/schwitalla_data
>> put "your files, 1 at a time"
>> bye
>>
>> Just let me know when you've posted the files.
>>
>> Thanks,
>> John
>>
>> Thomas Schwitalla wrote:
>>  
>>> John,
>>>
>>> when I try your suggestion, I got the following message:
>>>
>>> ERROR: process_grib_codes() -> no records matching GRIB code 54 with
>>> level indicator of Z0 found in GRIB file:
>>> /taifun/20070720_cops_WRF_sensitivity/assim/wrf_files/postprd/WRFPRS_2007072000_d01.002
>>>
>>>
>>>
>>> "wgrib -v" on this file gives:
>>>
>>> 171:80565400:D=2007072001:PWAT:atmos col:kpds=54,200,0:1hr fcst:winds in
>>> grid direction:"Precipitable water [kg/m^2]
>>>
>>> A sample line of my ASCII file reads:
>>>
>>> ADPSFC  0007  20070720_233700     52.9480     12.3922     60.9550  54
>>> -9999     60.9550     31.3000
>>>
>>> Now I am a bit confused...
>>>
>>> Thomas
>>>
>>> John Halley Gotway schrieb:
>>>    
>>>> Thomas,
>>>>
>>>> Just to be clear...
>>>> (1) Your forecast from WPP of precipitable water is a value that's
>>>> integrated over the whole column of air above each grid point.
>>>> (2) Your point observations of precipitable water are the same - a
>>>> value for the whole column of air above the observation point at the
>>>> surface.
>>>>
>>>> If that's true, I'd set up the PointStatConfig file as follows:
>>>> fcst_field[] = [ "PWAT/Z0" ];
>>>> message_type[] = [ "ADPSFC" ];
>>>>
>>>> That means "give me the precipitable water field with a level value of
>>>> 0", which is how's it's stored in your GRIB file.  And verify against
>>>> "surface" observations.  When you call ASCII2NC, be sure to
>>>> encode these PWAT observations using the "ADPSFC" message type.
>>>>
>>>> Give that a try and let me know if you have any problems.
>>>>
>>>> Thanks,
>>>> John
>>>>
>>>> Thomas Schwitalla wrote:
>>>>  
>>>>      
>>>>> John,
>>>>>
>>>>> I want to verify WRF forecasts (postprocessed with WPP)  with PWAT
>>>>> data
>>>>> from GPS stations. I already wrote it to NETCDF with ascii2nc but I
>>>>> haven't figured out how to edit PointStatConfig that I can use
>>>>> PWAT. My
>>>>> problem is: What value to set for the level type/code as PWAT is an
>>>>> integrated value?
>>>>>
>>>>> wgrib output looks as follows:
>>>>>
>>>>> PWAT kpds5=54 kpds6=200 kpds7=0 levels=(0,0) grid=255 atmos col 1hr
>>>>> fcst:
>>>>>
>>>>>
>>>>> Best regards,
>>>>> Thomas
>>>>>
>>>>>             
>>>     
> 
>