Jonathan Labriola-March 1-Convective Meteorology (Mesoscale Dynamics) Seminar

Convective Meteorology (Mesoscale Dynamics) Seminar

Analysis of Next-Day Hail Forecasts using Multi-Moment Microphysics Schemes for the 8 May 2017 Severe Hail Event in Colorado

Jonathan Labriola

Friday, March 1^st

3:30pm/NWC 5600

Day-ahead (20 – 22 hour) 3-km grid spacing convection-allowing model forecasts are performed for a severe hail event on 8 May 2017 using six different multi-moment microphysics (MP) schemes including: the Milbrandt and Yau double-moment (MY2), Thompson (THO), NSSL double-moment (NSSL), Morrison double-moment graupel (MOR-G) and hail (MOR-H), and Predicted Particle Properties (P3) schemes. Hail size forecasts diagnosed using the Thompson hail algorithm and storm surrogates predict hail coverage. For this case the storm surrogate updraft helicity produces the most skillful forecasts for severe hail because it identifies strong, rotating updrafts associated with storms capable of producing large hail. Hail size forecasts predict the coverage of hail with a high level of skill, but under-predict hail size. Hail size forecasts predict severe hail with low to moderate skill for microphysics schemes that predict large rimed ice (THO, MY2). NSSL hail size forecasts qualitatively improve when the maximum size of both hail and graupel is considered.

Model output is analyzed to access microphysical treatment of rimed ice. THO uses diagnostic parameters to increase the size of graupel within the hail core. MOR-G and MOR-H predict small rimed ice aloft; excessive size sorting and increased fall speeds cause MOR-H to predict more surface hail than MOR-G. The MY2 and NSSL schemes predict large, dense rimed ice particles because both schemes predict separate hail and graupel categories. The single ice category P3 scheme only predicts dense hail near the surface while above the melting layer large concentrations of low density ice dominate.