Lecture 24Outline of Last Lecture I. Thunderstorm HazardsII. What is Lightning?III. Lightning BoltIV. Charge SeparationV. Types of LightningVI. Cloud to Ground LightningVII. Sheet LightningVIII. Lightning StrokeIX. Lightning and ThunderX. Positive Polarity StrokeXI. Lightning SafetyXII. What is Hail?XIII. Lage Hail/HailXIV. Hail LayersXV. Flood StatisticsXVI. Types of FloodsXVII. Flash FloodsXVIII. Widespread FloodsXIX. Flood SafetyOutline of Current Lecture ATMS 100 1st EditionXX.What is a Supercell?XXI. Hook EchoXXII. Supercell StructureXXIII. Supercell EnvrionmentsXXIV. Outbreak: SummaryXXV. Supercell ComponentsXXVI. MesocycloneXXVII. Supercell RotationXXVIII. Wall CloudXXIX. Mammatus CloudsXXX. Forward Flank DowndraftXXXI. Rear Flank DowndraftXXXII. Types of SupercellsCurrent LectureXXXIII. What is a Supercell?a. Supercell thunderstorms are long-lived, rotating thunderstorm cellsi. can last for hoursii. often isolatediii. always rotateb. supercells are the strongest and most rare types of thunderstormsi. almost always sevreii. produce hail golfball sized and largeriii. produce nearly all violent tornadoesXXXIV. Hook Echoa. left/right side of nomenclatureb. may see hook echo on right-rear flank of stormi. indicative of rotationii. often associated with tornadoesiii. precipitation particles rotate around mesocycloneiv. first hook echo spotted UI on May 23rd, 1953XXXV. Supercell Structurea. precipitation formsb. strong winds aloft blow precipitation away from updraftc. precipitation falls downwind of updraft; forms foward-flank downdraftd. heaviest precipitation falls adjacent to updraftXXXVI.Supercell Envrionmentsa. Strong vertical Wind Sheari. winds change speed and/or direction with heightii. supercells will not rotate without itb. Low-level jeti. strong winds from south around 850 mb (1 mile)ii. provides low-level shearc. Jet Stream Alofti. strong westerly flowd. Instabilityi. warm moist air at surfaceii. cold air alofte. Triggeri. front, dryline, or outflow boundaryii. trough in jet stream to west (upper-level divergence)XXXVII. Outbreak: Summarya. 190 tornadoesi. super outbreak (4/3-4/74): 148 tornadoes confirmedb. 354 deaths (249 in AL)c. Super Outbreak: 315-330 deathsd. OKC Bombing (4/19/95): 168 deathse. Video: Tuscaloosa, AL (Tower Cam, FOX 9:39)XXXVIII. Supercell Componentsa. Updraftb. Mesocyclonec. Wall Cloudd. Anvile. Forward-flank downdraft (FFD)f. Rear-Flank Downdraft (RFD)g. Gust FrontsXXXIX.Mesocyclonea. persistent rotating updraftXL. Supercell Rotationa. air rotates about horizontal axis due to vertical wind shearb. updraft tilts this rotation into verticalXLI. Wall Clouda. a wall cloud is a lowered cloud beneath the updraft baseb. updraft ingests air with higher relative humidty (lower LCL) from down-draft regionsc. a rotating wall clouds indicates that a tornado may formXLII. Mammatus Cloudsa. mammatus clouds are sometimes seen hanginf from the anvil of thun-derstormsXLIII. Forward Flank Downdrafta. contains heavy rain, strong winds, and large hailb. visibility limitedXLIV. Rear Flank Downdrafta. visually the RFD appears as a clear slot near the updraft baseb. can sometimes see clear slot wrapping around the updraft (this is the RFD)c. Why?i.XLV. Types of Supercellsa. Classic Supercellsi. little rain near updraft, significant precipitation within foward flankii. prolific tornado producersb. High-Precipitation (HP) Supercellsi. significant precipitation near updraftc. Low-Precipitation (LP) Supercellsi. little precipitation everywhereii. narrow updraft