A Review of NCEP’s Convection-Allowing Model Guidance for the 20 May 2019 Southern Plains High Risk Day

This presentation will review mesoscale and convective-scale predictability challenges associated with the severe weather outbreak and flooding that occurred across the Southern Great Plains on 20–21 May 2019. In the lead-up to this event, model guidance indicated environmental conditions would be extremely favorable for numerous long-track, damaging tornadoes as well as other severe convective and flooding hazards. This led the Storm Prediction Center to issue a rare forecast of High Risk for severe weather across the region. A preexisting frontal boundary and elevated convection during the overnight and morning hours complicated the mesoscale environment across the region, and long-track, significant tornadoes did not occur to the extent that was anticipated.

Following this event, the Model Evaluation Group (MEG) at the National Centers for Environmental Prediction’s Environmental Modeling Center (NCEP/EMC) reviewed the performance of operational and experimental convection-allowing model (CAM) guidance. Highlights of that event review will be presented.

CAM guidance from NCEP’s NAM Nest, HRRR, and three HiResWindow systems provided a wide range of forecast solutions for the evolution of convection across Oklahoma, Kansas, and the Texas panhandle. The diversity in forecast solutions largely resulted from differences in how the models handled the elevated convection and its effect on the frontal boundary draped across north-central Oklahoma.

Details regarding the importance of appropriately initializing ongoing convection and associated mesoscale features will be discussed. Additionally, it will be shown that updraft helicity guidance from the HRRR may have signaled a more limited severe/tornado potential across the warm sector despite the numerous supercell-like structures seen in its forecasts. Finally, quantitative precipitation forecasts will be discussed briefly.