Basic WRF concept question

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Basic WRF concept question

Postby hatcherb » Wed Aug 05, 2009 1:15 pm

Hello -

Does the WRF actually forecast? Or does it model existing forecasts? For example, if I do a 48 hour run, initialized with GFS, it needs to be fed 48 hours with of forecast data from the GFS. Is it simply modeling the GFS forecast, or how exactly is that data used?

Apologies if the answer is obvious to most, but this is all very new to me. I'm a unix administrator by day, have a passion for the weather, and have a lot of idle hardware at home. So setting something like this up was only a matter of time, and I've gotten a lot of enjoyment out of setting up a cluster and crunching numbers. I ran through the excellent tutorial, but I'm still trying to fill in the conceptual gaps.

Thanks for reading!

-Bill

Edit: This probably should have gone under the model section - sorry :roll:
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Re: Basic WRF concept question

Postby jimmyc » Wed Aug 05, 2009 5:27 pm

Yes, you are making a forecast. The input data consists of the initial time from the GFS, and then uses the 48 hour GFS data to construct boundary conditions. The lateral boundary condition file uses 5 points at the edge (typically set in the namelist.input) of the domain to represent the atmospheric state outside the forecast domain.
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James Correia, Jr
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Re: Basic WRF concept question

Postby hatcherb » Wed Aug 05, 2009 9:45 pm

Thanks!

I've got a lot of blanks to fill in, but that was a really big one. Very much appreciated.
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Re: Basic WRF concept question

Postby joesko » Sun May 06, 2012 8:38 pm

Thank you jimmyc!!!

I've been searching everywhere for the answer to this, and now it makes total sense!! It seems like this should be made clear in the WRF websites, since its so fundamental to understanding what WRF actually does. My only question now is, how does NAM use WRF to make a "big forecast" that we can all use for our boundary conditions?
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Re: Basic WRF concept question

Postby jimmyc » Sun May 06, 2012 8:58 pm

The regional models like the NAM use a global model. So for example the 0000 UTC NAM gets its boundary conditions from the 18 UTC GFS forecasts.

Currently the model named NAM uses an NCEP variant of the WRF-NMM dynamic core called the NMM-B. The B is the grid type.

The NMM used an E grid staggering, while the ARW core uses C grid staggering (staggering referring to the way wind and mass fields are arranged on a cartesian grid).
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