Distance Learning Operations Course IC 5.7: Convective Storm Structure and Evolution Presented by the Warning Decision Training Branch Version: 0308.2 Distance Learning Operations Course Table of Contents Introduction ..................................................................................................... 1 Objectives ................................................................................................................................................ 3 Lesson 1....................................................................................................................................3 Lesson 2....................................................................................................................................3 Lesson 3....................................................................................................................................3 Lesson 1: Fundamental Relationships Between Shear and Instability on Convective Storm Structure and Type. ......................................................... 6 Objective 1 ............................................................................................................................................... 6 Effects of Shear .........................................................................................................................6 Objective 2 ............................................................................................................................................... 7 Objective 3 ............................................................................................................................................. 10 Midlevel Dry Air Promotes Stronger Downdrafts .....................................................................10 Effect on Storm Evolution Due to Vertical Placement of Dry Midlevel Air................................11 Downdraft Convective Available Potential Energy (DCAPE)...................................................12 Dichotomous Effects of Dry Midlevel Air .................................................................................12 Rules of Thumb for Mean Relative Humidity (RH) ..................................................................13 Inverse Relationship Between DCAPE and Mean Winds in Estimating Cold Pool Strength...13 Objective 4 ............................................................................................................................................. 14 Objective 5 ............................................................................................................................................. 17 Lesson 2: Definitions, Strengths, and Limitations of Environmental Param- eters ............................................................................................................... 19 Buoyancy ............................................................................................................................................... 19 CAPE ..................................................................................................................................................... 19 Model CAPE Discrepancies ....................................................................................................19 Importance of CAPE Density, 0-3 km CAPE ...........................................................................20 Convective Inhibition (CIN)......................................................................................................21 Lifting Condensation Level ......................................................................................................21 Shear ..................................................................................................................................................... 22 Minimum Shear for Supercells ................................................................................................22 Shear in Tornadic and Non-tornadic Supercells ......................................................................23 Storm-Relative Helicity (SRH)................................................................................................................ 24 Correlations in SRH and Tornado Intensity .............................................................................25 Can You Predict Maximum Tornado Intensity From SRH?......................................................25 SRH is a Better Supercell Forecasting Tool ............................................................................25 Depth of SRH to be Used........................................................................................................26 Midlevel Flow in Tornadic and Non-tornadic Storms ...............................................................27 Shear and Buoyancy Combinations....................................................................................................... 27 BRN.........................................................................................................................................27 BRN vs. BRN Shear ................................................................................................................28 Other BRN Limitations.............................................................................................................28 BRN Shear Values for Non-tornadic and Tornadic Supercells ................................................29 ii Table of Contents Table of Contents Energy Helicity Index (EHI) .....................................................................................................29 Vorticity Generation Parameter (VGP) ....................................................................................30 Summary................................................................................................................................................ 31 Lesson 3: Production and Detection of Severe Weather .......................... 32 Introduction ............................................................................................................................................ 32 Objective 6 ............................................................................................................................................. 33 Typical environment ................................................................................................................33 Ordinary cell evolution.............................................................................................................33 Objective 7 ............................................................................................................................................. 35 Weakly sheared cell motion.....................................................................................................35 Cautions About Using 0-6 km Mean Winds ............................................................ 36 Weakly sheared cell updraft considerations ............................................................................36 Updraft strength ...................................................................................................... 36 Objective 8 ............................................................................................................................................. 38 Updraft location and strength on radar ................................................................... 38 Storm top divergence .............................................................................................. 39 Downdraft strength ..................................................................................................................42 Objective 8a ............................................................................................................................45 Downdraft types ...................................................................................................... 45 Hail size...................................................................................................................................52 Objective 8b ............................................................................................................................56 Tornadoes in weak shear environments ................................................................. 56 Heavy rain potential.................................................................................................................59 Favorable conditions for high precipitation efficiency.............................................. 60 Objective 9 ............................................................................................................................................. 62 The effects of shear on storm structure...................................................................................62 Storm evolution in moderate shear ......................................................................... 63 Storm evolution in strong shear .............................................................................. 64 Objective 10 ........................................................................................................................................... 65 Dynamically Driven Low Pressure in Each Vortex .................................................. 66 Deviant supercell motions in straight shear. ........................................................... 66 Curved shear origins of rotation.............................................................................