Challenges Associated with Predicting High-Impact, Organized Convection in Weakly Forced Flow Regimes

Owing in large part to advances in numerical weather prediction (NWP), synoptic and mesoscale predictability have improved such that severe weather and flooding impacts resulting from organized convection can often be forecast with several days of lead time. Such extreme weather events are by in large associated with large-scale patterns that are highly predictable and provide strong forcings on the synoptic scale and mesoscale.

In more weakly forced, summertime flow regimes, predictability of hazardous weather resulting from organized convection is typically more limited. In such environments, diurnal convection and nighttime elevated convection can play significant roles in 1) causing severe weather and/or flooding impacts and 2) modifying the mesoscale and synoptic scale environments to promote subsequent organized convection and associated impacts. Successfully predicting the evolution of diurnal and overnight convection is a considerable challenge, even for convection-allowing models that assimilate radar data and frequently update. Shortfalling NWP guidance further poses significant challenges to local forecast offices as well as national centers like the Storm Prediction Center and the Weather Prediction Center.

Severe weather and flooding impacts resulting from weakly forced, organized convection were noted on numerous days in the late spring and early summer of 2018. NWP guidance for a selection of these cases will be examined by the Model Evaluation Group (MEG) at the NCEP/Environmental Modeling Center. Specific shortcomings and challenges for the suite of convection-allowing models run at NCEP will be presented, and context for future global and convection-allowing NWP will be discussed.