Creating 'blank' grids in grads

[P.R.]

Id like to know if its possible to create a blank, zero-valued grid without
a data-file, and then manually create a field of variables, and then fwrite
everything to a binary file.

Example:
I want to create my own 10meter (u,v) winds for a specific region, in order
to create a custom wind field for a simulation. I want the entire grid to
have 40 knt winds coming from 45 degrees, so I would need to derive my u & v
values for such a wind, and then fill the entire grid with these
values...Then, I would want to fwrite the entire grid to a fortran binary
file.

Is this possible and/or practical?
If so, then how would I go about creating this 'blank' grid without a data
file?
And, how could I go about manually defining my 'u' and 'v' variables for the
entire grid?

Or, is there an easier/more practical way to create such a grid with
arbitrary, user-defined data fields (such as for use in simulations)?

Please help,
Thanks,
P.Romero