[Wrf-users] help: Forecasting with WRF?

[Kevin Matthew Nuss]

Hi,

Just to fill in some details:

In the situation Elena described, the first GFS data set gets interpolated
over space to give initial conditions to the WRF grids. This data is in the
wrfinput files produced by real.exe. Then the first two data sets get
interpolated over space AND time to provide values but only for the outside
edges of  your WRF grid, not inside the WRF grid. This data is in the
wrfbdy file produced by real.exe. After the second data set is used up, the
boundary conditions are interpolated in time and space between the second
and third GFS data set. And so on. You can NOT forecast beyond the last GFS
data set because real.exe does not have a next data set to use for
interpolation. Without boundary conditions, the forecast can not continue
because no new weather can enter your WRF grid because it is not provided.
The GFS program is global so it has no boundaries (wraps around to itself).
GFS could continue on indefinitely. WRF, unless run as a global grid, has
to stop when there are no more boundary conditions to specify new weather
along its outside grid border.

If some of that was already obvious, sorry. Just trying to be complete and
of course, I don't know what you do or do not already know.
Kevin

On Tue, Jul 3, 2012 at 4:57 PM, Oleksandr Huziy <guziy.sasha at gmail.com>wrote:

> Hi,
>
> I can only tell you this as a guess, because I don't remember how it is
> done in wrf:
>
> 1) The 6h data is used on each time step as a boundary condition. They
> could linearly interpolate it in time to the time steps or just take the
> closest field to the current time step (or something more sophisticated).
>
> 2) You probably could do it for 6 more hours but then you would be using
> the same boundary conditions from the last 6 hourly forecast on each time
> step. In general I would say that this is not a good idea.
>
> Cheers
> --
> Oleksandr (Sasha) Huziy
>
> 2012/7/2 Elena Maria Pison San Pedro <emp at dhi.com.sg>
>
>> Hello,****
>>
>> ** **
>>
>> My question is regarding the capability of WRF to do forecasting. The
>> common utilization of WRF is using GFS (ex. 6hourly) with analysis or
>> forecasts files. Anyhow, WRF is running by itself between 2 GFS files, and
>> we can say, it is preforming a forecast of 6 hours. Am I right? ****
>>
>> ** **
>>
>> **-          **when the model arrives to the time step of the new GFS
>> file (time+ 6h), *how it integrates the information of the already
>> atmospheric situation and the info from the GFS new file*?****
>>
>> ** **
>>
>> **-          **Is it then *possible to run WRF beyond the last GFS
>> analysis* or longer than this intervals? ****
>>
>> ** **
>>
>> ** **
>>
>> Thanks a lot in advance!****
>>
>> ** **
>>
>> Cheers,****
>>
>> Elena****
>>
>> ** **
>>
>> ** **
>>
>> Elena Pison San Pedro****
>>
>> M.Sc. in Atmospheric Sciences****
>>
>>  ****
>>
>> [image: Description: Description:
>> C:\Users\mmc\AppData\Roaming\Microsoft\Signatures\dhi_logo.gif]****
>>
>>  ****
>>
>> DHI Water & Environment (S) Pte Ltd****
>>
>> 200 Pandan Loop****
>>
>> #08-03 Pantech 21****
>>
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>>
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>>
>> Tel:  ****
>>
>>  ****
>>
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>>
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>>
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>>
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>>
>> ** **
>>
>> ** **
>>
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