Rupert Klein Abstract This lecture will summarize two new developments, both based on the general multiple scales asymptotic framework for meteorological modelling which the author reported on in earlier presentations at the Courant Institute. The first part of the lecture will summarize two new systematic multiscale models for moist deep convection, developed jointly with A.J. Majda. One of these models is designed to address short time processes that involve the triggering of condensation and updrafts by convective scale linearized wave motions. These processes may be responsible for the onset of deep convection. Another model describes systematically larger length and time scales and covers flow regimes resembling fully established organized convection, as in strong weather fronts. The second part of the lecture will use the same asymptotic framework to motivate the design principles for a fully conservative low Mach and low Froude number numerical scheme for atmospheric applications. I will argue, in particular, how the classical concept of pressure based projection for anelastic flows can be extended to cover buoyancy dominated flow regimes relevant for bulk tropospheric flows.