FV3-LAM Convection-Allowing Model Forecasts and Ensemble Consensus Products for the Winter Weather Experiment

Recently the Center for Analysis and Prediction of Storms (CAPS) has run an ensemble of convection-allowing model (CAM) forecasts as part of the annual NOAA Weather Prediction Center Hydrometeorology Testbed (WPC-HMT) Winter Weather Experiments (WWE). For the 14^th WWE, 2023-24 the CAPS CAM ensemble comprised 11 members of the FV3 Limited Area Model (FV3-LAM) at ~3-km grid spacing over the contiguous United States (CONUS). The forecast ensemble and ensemble consensus products were produced for 37 case days within the WWE period (from late-November to mid-March). Specific forecast days of interest were determined in consultation with NWS forecasters via the HMT meteorologists at the Weather Prediction Center. Ensemble consensus products such as simple mean, probability matched (PM) mean, local-probability matched (LPM) mean were produced from the ensemble. In addition, novel consensus products including the Spatial Aligned Mean (SAM) and SAM-PM were produced from the ensemble.

Machine Learning probabilistic forecasts were also generated using all members of the operational High Resolution Ensemble Forecasting (HREF) along with 4 members of the CAPS FV3-LAM ensemble that had been run in previous winters. Individual members and ensemble consensus products were evaluated for their ability to improve on winter weather forecasting, particularly snow accumulation. A sample ML forecast case from the 13th WWE is shown in the sample image. Neighborhood maximum ensemble probability is plotted for 1-inch and 2-inch thresholds for 24h snowfall ending at 00 UTC 24 Jan 2023 alongside the NOHRSC verification snowfall.

The CAPS CAM ensemble was designed with a control member and 10 additional members with physics variations and/or variations in initial conditions and boundary conditions. The physics variations consisted of different combinations of microphysics, Planetary Boundary Layer (PBL), surface layer physics, and Land Surface Model (LSM).

Graphics products relevant to the forecasting of winter weather were produced, including 2-m temperature, liquid-equivalent precipitation and snowfall accumulation at 6- and 24-h intervals, precipitation type paintball plots, and precipitation type plots for each ensemble member. These graphics products are publicly viewable at https://caps.ou.edu/forecast/realtime/ .

Subjective and objective evaluations of the CAPS individual ensemble members, ensemble consensus products and machine learning probabilistic and deterministic products from recent Winter Weather Experiments will be presented at the meeting.