Abstract
Lake-effect snowstorms can produce large snowfall accumulations that are challenging to simulate and forecast. One source of forecast uncertainty for these events is the uncertain parameterization of sub-grid processes, such as planetary boundary layer and surface layer turbulence (PBL/SL) and cloud and precipitation microphysics (MP), in numerical weather prediction models. One way to quantify this uncertainty is to design ensembles that use stochastic parameter perturbations (SPP) to vary individual uncertain parameters within physics schemes. This research aims to evaluate and improve the utility of SPP for convection-permitting ensemble forecasts of lake-effect snow, with a focus on PBL/SL and MP parameterizations. We focus on a snowfall event observed during the Ontario Winter Lake-effect Systems (OWLeS) field campaign, which is simulated with 1-km horizontal grid spacing using the Weather Research and Forecasting model. A suite of 20-member ensemble simulations are run, including ensembles where SPP is applied only to PBL/SL or MP, where SPP applied to multiple schemes concurrently, where perturbations to initial and boundary conditions (ICs/BCs) are applied instead of SPP, and where SPP and IC/BC perturbations are applied together. SPP perturbations produce substantial spread in simulated precipitation, despite having only modest impacts on the synoptic-scale flow. They accomplish this by modulating lake-atmosphere fluxes, boundary layer characteristics, precipitation growth processes, and hydrometeor terminal fall speeds. The spread and skill of simulated precipitation from an ensemble using SPP alone is comparable to that from ensemble that uses IC/BC perturbations alone. The physical pathways whereby SPP perturbations generate spread are examined and discussed.
© 2025 American Meteorological Society. This is an Author Accepted Manuscript distributed under the terms of the default AMS reuse license. For information regarding reuse and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).
Massey Bartolini’s current affiliation: Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO
