Numerical
Weather Prediction in the Next Decade - Convective Forecasts with a
Global Atmospheric Model?
Bill
Skamarock
NCAR
10:30 a.m. August 21 in Room 2155
Abstract:
Convection permitting NWP uses regional models and short forecasts
periods because of computational constraints and the inherent
limitations of downscaling global forecasts. Using global models that
permit local refinement, existing computers are capable of producing
CONUS-scale explicit convective forecasts over intermediate-range
periods within operational time windows. The Model for Prediction
Across Scales (MPAS) uses an unstructured spherical centroidal Voronoi
mesh that allows for smooth cell-size variations between coarse and
fine resolution regions on the mesh, and we been using it to produce
experimental convective-scale global model forecasts. We will present
MPAS forecast results from the May 2015 NOAA Hazardous Weather Testbed
forecast experiment, and MPAS forecasts supporting the Plains Elevated
Convection at Night (PECAN) experiment, that demonstrate these MPAS
capabilities. Two issues are addressed with the MPAS configuration in
these forecast experiments. First, forecast results show that the
problems inherent in traditional grid-nesting approaches are not
evident in the MPAS variable-mesh forecasts. Second, we are using the
scale-aware version of the Grell-Freitas convective parameterization,
and we find that it transitions appropriately from parameterizing
essential all the unstable deep convection at hydrostatic-scale mesh
spacings to allowing the convection to be explicitly simulated at
nonhydrostatic mesh spacings on the variable resolution mesh. We will
discuss our experience with these issues within the context of these
and other forecast tests.