In case of full distribution we started with a new directory so we can unpack right away:
$
gunzip wfc_full-038.023.tar.gz
Which reveals file wfc_full-038.023.tar
which can be untarred with:
$
tar xf wfc_full-038.023.tar
There are several ways to do the trick. Another is:
$
gzcat wfc_full-038.023.tar.gz | tar xf -
or
$
gtar wfc_full-038.023.tar.gz