Science Source
The Impact of Vertical Wind Shear on Hail Growth in Simulated Supercells
- States that severe hailstorms produce over $1 billion in insured losses annually in the United States, yet details of a given storm’s hail threat (e.g., maximum hailstone size and total hailfall) remain challenging to forecast
- Previous research suggests that, in addition to maximum updraft speed, the storm-relative airflow could be equally important for hail formation and growth
- This study investigates how changes in environmental wind shear and subsequent changes in simulated supercell storm structure affect hail growth
- Performs 20 idealized simulations in which the thermodynamic profile remains fixed but the environmental hodograph is systematically altered
- Quantifies hail growth using the hail mass mixing ratio from composites of storms over the last hour of simulation time
- Computes hailstone growth “pseudotrajectories” from these storm composites to determine favorable embryo source regions
- Results indicate that increased deep-layer east–west shear elongates the storm’s updraft in that direction, providing:
- (1) increased volumes over which microphysically relevant hail processes can act
- (2) increased hailstone residence times within the updraft, and
- (3) a larger potential embryo source region; together, these lead to increased hail mass
- Finds that increased low-level north–south shear, which results in hodographs with increased 0–3-km storm-relative helicity, also elongates the updraft in the north–south direction
- Finds that hail mass is reduced owing to a separation of favorable embryo source regions (which shift southward) and available hydrometeors to serve as embryos (which shift northward)
