Verifying the Impact of the FV3-GFS Upgrade on LAMP Statistical Guidance

As part of its Next Generation Global Prediction System (NGGPS) initiative, the National Weather Service (NWS) is upgrading the Global Forecast System (GFS) from a spectral model to a Finite Volume Cubed Sphere Dynamical Core (FV3) based model. The FV3-GFS upgrade is the first step towards a fully integrated and flexible modeling framework which will optimize available computing capabilities. Changes to the dynamical core do not only impact the GFS itself, but also affects the multitude of postprocessed products that utilize the GFS as an input. One such product is Localized Aviation Model Output Statistics Program (LAMP) which provides rapidly updating short-term guidance for aviation forecasters and supports the National Blend of Models (NBM). LAMP uses numerical model output and observations to provide guidance for weather elements that are particularly impactful for aviation such as ceiling height and visibility. Through statistical postprocessing using multiple linear regression techniques, LAMP aims to mitigate the systematic biases that are inherent in modeled forecasts. However, upgrading the GFS could degrade the LAMP guidance by altering the characteristics of the bias profile that LAMP was developed to account for.

In this study, we evaluate whether the FV3-GFS meaningfully impacts the LAMP guidance. To do so, verification statistics are calculated for six months of LAMP forecasts using input guidance from the operational GFS and the retrospectively run FV3-GFS. The retrospective FV3 dataset that enabled this analysis was provided by the Environmental Modeling Center (EMC) and spanned dates from January through July 2018. The verification statistics that resulted from this analysis provided a quantitative measurement of the impact of the FV3-GFS upgrade on LAMP guidance over this time period. This presentation will detail the evaluation plan that resulted in these verification statistics as well as outline the conclusions that emerged from this process. Case studies will also be shown highlighting the impacts of the FV3-GFS upgrade on LAMP and Gridded LAMP guidance.