1240 Results of Varying Vertical Grid Resolution and Microphysics in 3-km FV3 Stand-Alone Regional Runs

Wednesday, 15 January 2020
Hall B (Boston Convention and Exhibition Center)
Eric Aligo, EMC/NCEP/NWS/NOAA and I.M. Systems Group, Inc., College Park, MD; and E. Strobach, Y. Lin, L. C. Dawson, J. R. Carley, and J. S. Kain

EMC is currently running two experimental 3-km FV3 standalone regional (SAR)
configurations using the current 64 level operational GFS vertical grid resolution (VGR) and
GFDL microphysics scheme. Preliminary results of the experimental runs indicate the 3-km
FV3 SAR has a high bias in the heaviest precipitation during the warm season, and storm
structure lacks the fine-scale details that can be seen in both observed and in 3-km operational
NAM nest simulated composite reflectivity forecasts. Additionally, the experimental SAR did
not capture the non-linear convection that produced destructive tornadoes in the Southeastern US
tornado outbreak from March 03 2019.

In attempt to address the precipitation biases, the lack of storm structure, and the lack of
pre-convective line activity in the March 03 2019 tornado outbreak, sensitivity runs were made
with the 3-km FV3 SAR varying the vertical grid resolution (VGR) and the microphysics
scheme. Sensitivity runs were made using the 60 level NAM VGR, which has 17 levels in the
lowest 100 hPa above the surface. With the lowest model level in both the operational GFS and
NAM at approximately 20 m above ground level (agl), and closer to 10 m agl in the operational
HRRR, runs were made using the NAM VGR and a lowest level of 10m agl. Results from
sensitivity tests comparing the GFDL microphysics to the Thompson microphysics will also be
shown with an emphasis on precipitation impacts. Special attention will be given to vertical
profiles in the different VGR runs in addition to an evaluation of storm initiation, mode, and
vertical structure of MCSs using reflectivity and other microphysics related fields.

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