  Dwarf nova outbursts often show coherent ($Q\sim10^4-10^6$) sinusoidal
oscillations with the largest pulsed fraction in the extreme ultraviolet.
Called dwarf nova oscillations (DNOs), they have periods of $P\approx3-40 {\rm
s}$ and scale with luminosity as $P\propto L^{-\beta}$ with
$\beta\approx0.1-0.2$. We propose that DNOs may be produced by nonradial
oscillations in a thin hydrostatic layer of freshly accreted material, the
``spreading layer'' (SL), at the white dwarf (WD) equator. This would naturally
explain a number of key properties of DNOs, including their frequency range,
sinusoidal nature, sensitivity to accretion rate, and why they are only seen
during outburst. In support of this hypothesis we construct a simple model that
treats the SL as a cavity containing shallow surface waves, each with the same
radial structure, but split into three different modes denoted by their
azimuthal wavenumber, $m$. The $m=0$ latitudinally propagating mode best
matches the periods and scalings associated with most DNOs, and DNOs with
periods shorter than the WD Keplerian period are explained by the $m=-1$
prograde mode. We also predict a third set of oscillations, produced by the
$m=1$ retrograde mode, and show its expected dependence on accretion rate.
