Precipitation Processes within an Alberta Supercell Hailstorm

Terrence W. Krauss Department of Atmospheric Science, University of Wyoming, Laramie, WY 82071

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John D. Marwitz Department of Atmospheric Science, University of Wyoming, Laramie, WY 82071

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Abstract

An investigation was made into the precipitation processes operating within an Alberta supercell hailstorm which occurred on 22 July 1979. The main research tools employed in the study were an instrumented aircraft and an S-band meteorological radar.

Five cloud penetrations were conducted in and around the bounded weak-echo region associated with the main updraft of the storm during a 40 min period while the storm was producing 2–5 cm diam hail at the surface. The main updraft consisted of a relatively smooth, steady flow with adiabatic temperature. The main updraft acted as an obstacle to the mid-level environmental flow and caused the winds to split and accelerate around the southern side. Several smaller turbulent updrafts associated with time-dependent, fine-scale convective cells (feeder clouds) existed adjacent to the main updraft and appeared to be superimposed onto the quasi-steady, broader-scale dynamically forced circulation of the main storm. Graupel particles which originated within the feeder clouds were transported by the mid-level winds into and across the weak-echo region.

This study provides evidence that feeder clouds are also found within storms classed as supercells and that they provide a viable source of hailstone embryos and present a vital link among hail formation processes within a broader-scale continuum of hailstorm structures.

Abstract

An investigation was made into the precipitation processes operating within an Alberta supercell hailstorm which occurred on 22 July 1979. The main research tools employed in the study were an instrumented aircraft and an S-band meteorological radar.

Five cloud penetrations were conducted in and around the bounded weak-echo region associated with the main updraft of the storm during a 40 min period while the storm was producing 2–5 cm diam hail at the surface. The main updraft consisted of a relatively smooth, steady flow with adiabatic temperature. The main updraft acted as an obstacle to the mid-level environmental flow and caused the winds to split and accelerate around the southern side. Several smaller turbulent updrafts associated with time-dependent, fine-scale convective cells (feeder clouds) existed adjacent to the main updraft and appeared to be superimposed onto the quasi-steady, broader-scale dynamically forced circulation of the main storm. Graupel particles which originated within the feeder clouds were transported by the mid-level winds into and across the weak-echo region.

This study provides evidence that feeder clouds are also found within storms classed as supercells and that they provide a viable source of hailstone embryos and present a vital link among hail formation processes within a broader-scale continuum of hailstorm structures.

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