Supercells Eric A. Pani The University of Louisiana at Monroe

Overview Less frequent that single- or multi-cell storms Often produces hail and/or damaging winds Of size similar to multi-cell storms but consists of single, giant updraft- downdraft couplet Updraft rotates (Source: after

Appearance (Classic) (Source: Visual: Overshooting top Overhanging anvil Wall cloud under most active towers in area free of precip Feeder vs. daughter cells Mammatus Radar: Large precipitation area (PPI) Hook echo (PPI) BWER (RHI)

Appearance (Heavy Precipitation) (Source: Visual: Inflow band (tail cloud) No longer have rain-free base Vivid lightning displays Tornado often surrounded by precip Most common in southeastern US Radar: Broad hook (PPI) Distinct inflow notch (PPI) WER (RHI) High reflectivities

Appearance (Low Precipitation) (Source: Visual: Develops along dry line (dry air to west, moist air to east) Smaller than HP or classic supercell Much less liquid precipitation Radar: Hook usually not present (PPI) Tight reflectivity gradient on SW flank (PPI) Intensity often underestimated (incomplete beam filling)

Weak echo region (Source: Chisholm and Renick, 1972) (Source: Process: strong updraft prevents precipitation formation

Updraft and FFD (Source: 89video/19.md.gif) Updraft enters at low levels from southeast and rises nearly vertically Mid-level inflow of dry air enters from southwest, wraps around updraft and sinks in forward-flank downdraft Cause of negative buoyancy is evaporative cooling

Rear flank downdraft (Source: OS/89video/20.md.gif) Additional dry air enters at mid-levels from south, wraps around updraft, and sinks as rear-flank downdraft Source of negative buoyancy may be melting of hail

Rotation (Source: sa.uiuc.edu/AO S/89video/21.m d.gif) Rotation source may be Horizontal vorticity generated by low-level shear and tilted into vertical Solenoids generated along outflow boundary

Vorticity Equation 1. Local change in relative vorticity 2. Advection of relative vorticity 3. Convergence term 4. Twisting-tilting term 5. Advection of earth’s vorticity 6. Solenoid term

Simulation 1

Storm motion Storm usually moves to right of mean wind  Magnus force  Forcing from mid-level vortices V increases p decreases V decreases p increases

Storm splitting Often see storms split, producing left- and right-moving systems Splitting related to vertical PGFs established by vortices Pressure decreases in each vortex as fields adjust into cyclostrophic balance New updraft regions form and cells move apart from Magnus force and inflow Left-moving system tends to weaken because of negative vorticity (Source: Klemp, 1987)

Families of tornadoes (Source: Burgess et al., 1982)

Synoptic setting

Simulation 2