  We introduce simple analytic expressions for the neutrino survival
probability in media valid in the quasi-adiabatic limit. These expressions
provide a quick but accurate alternative to numerical solution of the neutrino
propagation equations for the Mikheyev-Smirnov-Wolfenstein effect. They can
also be used to extract information about the density scale height from the
neutrino data. As an example, we present calculations for solar neutrinos.
