[Met_help] threshold values

[John Halley Gotway]

Mike,

Both Grid-Stat and Point-Stat are set up to run only once per valid time. 
Neither handle multiple output times in a single run.  We do expect that
people will script calls to the tools to handle multiple times.

Thanks,
John

> One option that could be useful is an option in grid_stat, like in the
> point_stat, for specifying multiple files/timesteps to generate statistics
> for.  ...unless it exists and I haven't found it yet!  I might try and do
> this (or just run it recursively in a script for single grid_stats for a
> series of comparisons) - but if you get to it first or can point me to how
> I might do this, let me know.
>
> Thanks,
> Mike
>
> -----Original Message-----
> From: John Halley Gotway [mailto:johnhg at ucar.edu]
> Sent: Wednesday, April 21, 2010 10:54 AM
> To: Shaw, Michael J CTR USAF AFWA 16 WS/WXE; met_help
> Subject: Re: threshold values
>
> Mike,
>
> Yes, that's correct.  You can currently only apply masks one at a time and
> there is no mechanism for taking the intersection (or union) of multiple
> masks.  However, adding that type of functionality
> would be feasible.  Is that something that would be useful in your work?
>
> Thanks,
> John
>
> Shaw, Michael J CTR USAF AFWA 16 WS/WXE wrote:
>> Thanks.
>>
>> And...looks like can't mask with the intersection or union of two masks,
>> right?  (E.g., mask the intersection of EAST poly and obs > 20.)
>>
>> -----Original Message-----
>> From: John Halley Gotway [mailto:johnhg at ucar.edu]
>> Sent: Tuesday, April 20, 2010 5:16 PM
>> To: Shaw, Michael J CTR USAF AFWA 16 WS/WXE; met_help
>> Subject: Re: threshold values
>>
>> Mike,
>>
>> Yep, I was just writing you a message about that.  Let me know if that's
>> sufficient for you.  Or if there's an enhancement you'd like to see to
>> "filter" the raw values using a threshold before
>> computing continuous statistics, we could add that the list of requested
>> upgrades for future development.
>>
>> Thanks,
>> John
>>
>> Shaw, Michael J CTR USAF AFWA 16 WS/WXE wrote:
>>> Ah - I'm seeing I can also threshold the masks.  I.e., use the mask for
>>> obs, e.g., for values greater than 20mm and compare the model...
>>>
>>> Thanks,
>>> Mike
>>>
>>> -----Original Message-----
>>> From: John Halley Gotway [mailto:johnhg at ucar.edu]
>>> Sent: Tuesday, April 20, 2010 5:05 PM
>>> To: Shaw, Michael J CTR USAF AFWA 16 WS/WXE
>>> Cc: 'met_help'
>>> Subject: Re: threshold values
>>>
>>> Mike,
>>>
>>> I think there's some confusion about how the thresholds you set in the
>>> "fcst_thresh" and "obs_thresh" parameters of the configuration file are
>>> actually used by MET.  The Grid-Stat and Point-Stat tools
>>> compute a variety of different statistics, and those statistics are
>>> grouped together by type.  Two of those group are the "continuous" and
>>> "categorical" statistics.  The continuous type statistics are
>>> all grouped together into the CNT lines.  The categorical type
>>> statistics are all grouped together into the CTS lines.
>>>
>>> Continuous statistics are computed using the raw data values in the
>>> fields.  Whereas categorical statistics are computed by applying
>>> thresholds to the forecast and observation fields to create fields
>>> of 0's and 1's, defining contingency tables, and deriving statistics.
>>> As you change the threshold values, those contingency table counts and
>>> corresponding statistics will change.
>>>
>>> However FBAR is a continuous statistic computed over the raw data
>>> values.  It's just the mean of the forecast values in the verification
>>> region.  There is no thresholding involved.  When you look at
>>> an output CNT line from MET, the "fcst_thresh" and "obs_thresh" values
>>> in that line should be set "NA", meaning that thresholds do not apply.
>>>
>>> Hope that helps straighten it out.  You can find more information about
>>> this in the MET User's Guide.
>>>
>>> John Halley Gotway
>>> met_help at ucar.edu
>>>
>>> Shaw, Michael J CTR USAF AFWA 16 WS/WXE wrote:
>>>> Hi.
>>>>
>>>> When I include a forecast thresh of 0 and fcst thresh of 20, masked
>>>> over a region (EAST poly), I get the same average of precip
>>>> (accumulated over a week or so) of about 13.5.  As in identical FBAR.
>>>> I'm obviously missing something - I wouldn't think a mean of 13.5
>>>> would be possible if I'm using only values >20.
>>>>
>>>> What am I missing?
>>>>
>>>> Thanks,
>>>> Mike
>>>>
>>>> ______________________________________________
>>>>
>>>> Michael Shaw, Contractor
>>>> SAIC/NASA Support Scientist
>>>> michael.shaw.ctr at offutt.af.mil
>>>> 16WS Environmental Characterization
>>>> HQ AFWA-SAIC
>>>> 101 Nelson Drive
>>>> Offutt AFB, NE 68113-1023
>>>> 402-232-7690 Comm * 402-272-7690 DSN * 402-294-8230 Fax
>>>>
>>>>
>