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That usually applies from the ground up to about 1,000 feet with a stronger wind at higher altitudes. Above about 1,000 feet wind patterns may be different. I could add then, if you are trying to factor in where fallout might go after the initial outward directions at blast time, it tends to go with the lower third of the atmosphere but also quite a bit of fallout will elevate above that and go further. Usually recent satellite imagery will give you an idea of the direction of motion of those parts of the atmosphere since water vapour acts in roughly the same way.

Also at a distance from source, fallout will be relatively greater with rainfall as it can then be transported more easily back to the surface. This was the experience after the relatively small fallout clouds from Chernobyl.

At first any massive strikes would “make their own weather” especially if several were close together, but eventually, that effect would fade out and the large amounts of fallout equally distributed around targets would begin to move in some semi-organized way, more than likely from west to east but not always. When Chernobyl blew up, Ukraine was lucky in that the prevailing lower level winds stayed southeast for days and took most of the fallout up over Belarus, the Baltic States and Sweden. As it turned out, even Sweden got more radiation than Kiev just a hundred miles southeast of the plant. It could have turned out very bad for Kiev in a different pattern (or even for Moscow).