Forecasting: Why Clouds Have Clearly Defined Boundaries

Understanding Weather and Climate (7th Edition) (MasteringMeteorology Series) by Edward Aguado, James E. Burt

Multi-Cellular Thunderstorms

Ø  Multi-cell Thunderstorms

̶        Dominated by gust front processes

̶        Add more shear (from single cell thunderstorms)

̶        Flanking line towers become other storms

Ø  Multi-cell Cluster

̶        Series of evolving cells where new updraft growth is on a preferred flank

̶        Mean wind of the cloud barring layer

̶        New cells more where the low level convergence is the strongest

̶        Deviates (Verb)

̶        Deviant (adjective)

̶        In moderate wind shear environments, multi-cell storms may take a few hours to evolve into a supercell storm

̶        In a squall line new squalls form on the continuous gust front (leading edge)

Ø  Line Echo Wave Patterns (LEWP)

̶        Series of bow echoes

̶        A wavy appearing squall line

̶        Can result in an enhanced severe threat at the leading edge of the bow or in the “crest” of the waves

̶        Sometimes can get a small vortex within the line (tornado)

̶        Not a supercell tornado, it’s a QLCS tornado

Ø  QLCS (Quasi Linear Convective System)

̶        Somewhat a line

̶        Can produce tornados (usually weak)

Ø  Supercell:

̶        Storm with a  Mesocyclone

Ø  Mesocyclone:

̶        Strong and persistent

Ø  Squall Line Cross Section

̶        Compare with super cell schematic

̶        Updrafts are on the leading edge of the cold pool, hence tornado threat is small after passage of gust front although hail will now occur

̶        Squall lines have well-developed cold pools

̶        Surface based: Warm air from the ground is going straight up

Ø  Cross Section of multi-cell

̶        Continuous gust front

Ø  Outflow Boundary (OFB)

Ø  OFB on Composite radar

̶        Land spouts