[Met_help] NAM and GFS question

[John Halley Gotway]

Holly,

I really have not worked with verifying TMIN and TMAX in the past.  What you're planning on doing sounds reasonable, but in talking to a scientist here about it, she made a good point.  If you're only
using 3-hourly GFS and NAM data, the min/max temperature values may actually occur somewhere inbetween those 3-hr time intervals.  So taking the min/max by looking at the instantaneous temperature
every 3 hours would only give you a pretty rough estimate of the actual min/max values.

There isn't currently a tool in MET to do this sort of thing.  However, if I were in your shoes, I'd modify the PCP-Combine tool to do this for you.  I'd suggest running the PCP-Combine tool in the
"-sum" mode.  By supplying the "-gc 11" argument, it can be run over temperature fields.  If you were to do that, the values you'd get out would be the sum of the temperatures over those 8 files.  But
it wouldn't be too hard to modify the code to take the "min" or "max" instead of summing it up.

Hope that helps and good luck.

John

Holly Hassenzahl wrote:
> Hello John-
> 
>  
> 
> Happy Friday!  We are about to expand our verifications out to the raw
> NAM and GFS models.  However, questions have come up about how to
> accurately extract the TMIN and TMAX variables, since neither of these
> global models actually output those variables...only TMP every 3 hours. 
> 
>  
> 
> Have you or anybody you know verified TMIN and TMAX against NAM and/or
> GFS?  We are contemplating writing something that would filter the temps
> over a 24-hour period to determine the max and min.  Before we do that,
> is there a tool in the MET software that would be able to take 8 input
> grids over a 24-hour period and create TMIN and TMAX grids as the
> output?  Or do you have any other suggestions that would be helpful?
> 
>  
> 
> Just wanted to pick your brain a little bit and see if you've
> encountered this before.  Thanks...
> 
> Holly
> 
>  
> 
> ___________________________________
> 
> Holly C. Hassenzahl
> 
> Meteorologist, Science Analyst
> 
> Data Products Group
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>  
> 
> Weather Central, Inc.
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