EAS 486 Lecture Content for Day 10: Behavior of Isolated Storms - Introduction

The lecture content included:

  1. Behavior of Isolated Storms (Bluestein Section 3.4, especially pp. 455-492)
    1. Prologue: Hodographs
      1. Hodograph depict vertical vector wind shear graphically
      2. The line that would connect the tips of the wind vectors in the sounding
      3. Done in polar coordinates
      4. Points labelled by elevation
        1. Standardly in km
        2. Often seen with some reference to pressure
      5. Examples: College of DuPage, UCAR Upper-Air Menu, University of Wyoming Sounding Menu
      6. Empirical observation (pre-1980) that vertical wind shear has some relation to the organization of severe thunderstorms.
    2. Rules of development based upon convective modeling studies performed by Klemp, M. Weisman, Rotunno at NSSL 1979-1983
    3. General Storm Types
      1. Single Cell (see Fig 3.15, p. 457)
        1. Single updraft
        2. Life Cycle: 30-50 min
        3. Downdraft "drowns out" updraft
        4. Downdraft produced by
          1. Evaporational cooling by drier air.
          2. Sources:
            • Entrained drier air surrounding the cloud
            • Unsaturated air underneath cloud base
          3. Drag of falling hydrometeors
        5. Can produce severe weather in mature phase (both updraft and downdraft present)
      2. Multicell Storm
        1. Cluster of short-lived single cells
          1. Each cell in different stage of life cycle
          2. Long lasting due to successive redevelopment
        2. Cold outflow from each cell combine to form gust front
        3. Strongest new convection usually in direction of storm motion
          1. New updrafts form along and just behind gust front.
        4. Storm motion can deviate dramatically from the mean wind due to successive cell development in the unmodified air mass (See Fig 3.17)
        5. Squall line - Worst weather at front of storm (Fig. 3.79, p. 527, and Fig. 3.83 , p. 531)
          1. Straight line damaging winds
          2. Hail
          3. "Gustnado" - tornado along or near gust front
        6. More stratoform precipitation at the rear of leading line
        7. Dynamics (PRE-STORM 1982)
          1. Front-to-rear updraft at top of the storm
          2. Rear-to-front jet (downdraft)
            1. Can lead to "bow echo" formation (straight line wind outbreak) due to inflow of entrained air from back of storm

Last updated: 03-Mar-2009 10:25 AM

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