[Met_help] Re: MET -- grid conversion on GFS

John Halley Gotway johnhg at rap.ucar.edu
Mon Nov 5 13:11:40 MST 2007


You have a few options...

(1) You could continue re-gridding your forecasts to the GFS grid and compare them directly.  If you do so, I'd recommend setting the "mask_missing_flag" in the MODE config file to a value of 3.
Then, prior to defining objects, MODE will mask out data in both the forecast and observation fields where at least one of the fields has missing data.  So you'll end with objects only where there's
valid data in both fields.

However, you'll still end up with plots that don't look very nice.  The whole domain will be plotted, so the region of valid data will be relatively small.  We've addressed this issue in the next
release with the "plot_valid_flag".  Turning on this flag tells MODE to zoom the plot up to only the valid region of data.  So you could use that when the next release comes out.

(2) You could define a new grid that's a subset of the GFS domain but similar to your forecast domain, and re-grid both the forecast and observation files to that new grid.  You mentioned having
difficulty defining such a grid.  I'd be happy to help you figure out the arguments for "copygb" to define such a grid.  I'd just need you to send me one of your forecast grib files and one of the GFS
observation grib files.  I'll pull out the grid definition information from the files and see what I can come up with.

(3) You could continue re-gridding the observations to your forecast domain.  I doubt the issue of putting the forecasts onto the observation grid is as big of an issue with an "object-based" approach
like MODE as it is with a traditional point-based or grid-based verification approach.  I wrote a couple of the statisticians in our group about this issue but haven't heard back from them yet.  I'll
let you know what I find out.

Please let me know which route you'd like to go.  Whichever you choose, I'd still recommend using the "mask_missing_flag" in the MODE config file.  It only really makes sense to define objects where
you have valid data in both fields.

And if you'd like help defining a new grid, just send me those sample files and I'll see what I can do.


Luke Peffers wrote:
> Hello John:
> I am have some difficulty verifying my WRF model run with GFS gridded date.
> I would like to follow the general rule that when comparing two gridded
> files, one should regrid the forecast file to the obs grid, in my case GFS.
> When I do that, mode compares my relatively small domain to the entire GFS
> (global) domain.
> I am, of course, running my WRF output through WRF Post Processor.   I
> regrid my files using COPYGB.
>  I have no problem regridding the GFS data to my forecast grid since I know
> the exact grid dimensions for the user defined grid from WRF.  I don't,
> however, know the exact grid codes for a GFS-like grid that is of the exact
> domain size of my forecast file. Thus, I continue to use MET with obs files
> regridded to match my WRF output grid file.
> Do you know how I can resolve this problem?
> Thank you!!
> Luke Peffers
> FSU Meteorology Department

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