  The warp is a well-known undulation of the Milky Way disc. Its structure has
been widely studied, but only since Gaia DR2 has it been possible to reveal its
kinematic signature beyond the solar neighbourhood. In this work we present an
analysis of the warp traced by Classical Cepheids by means of a Fourier
decomposition of their height ($Z$) and, for the first time, of their vertical
velocity ($V_z$). We find a clear but complex signal that in both variables
reveals an asymmetrical warp. In $Z$ we find the warp to be almost symmetric in
amplitude at the disc's outskirts, with the two extremes never being
diametrically opposed at any radius and the line of nodes presenting a twist in
the direction of stellar rotation for $R>11$ kpc. For $V_z$, in addition to the
usual $m=1$ mode, an $m=2$ mode is needed to represent the kinematic signal of
the warp, reflecting its azimuthal asymmetry. The line of maximum vertical
velocity is similarly twisted as the line of nodes and trails behind by
$\approx 25^\circ$. We develop a new formalism to derive the pattern speed and
change in amplitude with time $\dot{A}$ of each Fourier mode at each radius,
via a joint analysis of the Fourier decomposition in $Z$ and $V_z$. By applying
it to the Cepheids we find, for the $m=1$ mode, a constant pattern speed in the
direction of stellar rotation of $9.2\pm3.1$ km/s/kpc, a negligible $\dot{A}$
up to $R\approx 14$ kpc and a slight increase at larger radii, in agreement
with previous works.
