THUNDERSTORMS
PART I: MORPHOLOGY of a MESOSCALE SYSTEM
Summer 1999
Lecture #23 Scheduled for:
28 JUL 1999 (W)
Recommended Readings from Moran and Morgan (1997):
pages 307-319; 139-142.
pages 307-319; 139-142.
Today's Lecture Objectives:
To provide a definition of a thunderstorm.
To identify the relative size of a thunderstorm.
To define atmospheric instability and identify the atmospheric stability
criteria.
To identify the types of thunderstorms that commonly occur throughout the
United States.
To locate the regions in the United States having maximum (minimum) annual
frequency of thunderstorms and offer an explanation for the occurrence
of high (low) numbers of thunderstorms.
To explain why thunderstorms are typically a summertime phenomena.
To identify the various mechanisms whereby thunderstorms develop.
To identify and describe the properties of each of the three stages of
a thunderstorm's life cycle.
To sketch the internal thunderstorm structure and to identify the various
special clouds associated with the thunderstorm cell.
To list the criteria used to identify severe weather.
To sketch the synoptic weather pattern that favors development of severe
thunderstorms.
To explain why some thunderstorms become severe.
To differentiate between a "severe thunderstorm watch" and "severe thunderstorm
warning".
Outline:
A. INTRODUCTION
Practical Questions
Definitions
The Human Factor
B. THUNDERSTORM GENESIS
Essential Ingredients
Initial Setting and Initiation Processes
Stability Criteria
The "Trigger"
C. THUNDERSTORM TYPES
Single-Cell Thunderstorms
"Air Mass" Thunderstorms
Orographic Thunderstorms
Frontal Thunderstorms
Multiple-Cell Thunderstorms
Squall-Line Thunderstorms
Mesoscale Convective Complexes (MCC)
D. THUNDERSTORM CLIMATOLOGY
Geographical and Seasonal Distribution
Time of Day
Duration of Thunderstorms
Reported Thunderstorm Intensities
E. CHARACTERISTICS OF SINGLE CELL THUNDERSTORMS
The Thunderstorm Cell Model
Spatial Dimensions
Life Cycle of a Non-Severe Thunderstorm Cell
Cumulus Stage
Mature Stage
Dissipating Stage
Thunderstorm Weather Sequences near the Earth's Surface
Rainfall
Wind Field
Air Temperature
Barometric Pressure
F. SEVERE THUNDERSTORMS
Criteria for Severe Weather (Official)
Types of Severe Thunderstorms
Structure of Severe Thunderstorms
Synoptic Situations Favoring Severe Thunderstorm Weather
Last revision 26 May 1999
Produced by Edward J. Hopkins, Ph.D.
Department of Atmospheric and Oceanic Sciences
University of Wisconsin-Madison Madison, WI 53706
hopkins@meteor.wisc.edu