ATM OCN (Meteorology) 100

MIDLATITUDE WEATHER SYSTEMS
PART II: THE EXTRATROPICAL CYCLONE

Summer 2001

Lecture # 20 Scheduled for:

18 JUL 2001 (T)

2 JUL 2001 (W)

Recommended Readings from Moran and Morgan (1997):

pages 261-272; 272-276; 391-394.

Today's Lecture Objectives:

• To describe briefly the contribution made to meteorology by the Norwegian School with the polar front cyclone model.
• To identify the relative size and characteristics of an extratropical cyclone.
• To locate and describe the general temperature-field, the wind regime and the cloud and precipitation pattern associated with a model extratropical cyclone.
• To locate the regions of greatest pressure change with respect to time in a migratory extratropical cyclone.
• To outline the sequence of stages in the life cycle of a migrating midlatitude wave cyclone.
• To relate the features associated with a surface extratropical cyclone and the upper tropospheric wind regime.
• To identify regions of cyclogenesis and the major storm tracks across North America.
• To distinguish between warm frontal weather and cold frontal weather and their associated weather sequences during frontal passage.
• To describe the weather sequences (i.e., changes in wind direction, pressure tendency, cloud type and coverage, precipitation and temperature) when the warm or cold side of a wave cyclone passes an observer.
• To locate the position and forecast the movement of an extratropical storm by interpreting the sequence of wind direction, pressure change, temperature change and cloud/precipitation type at a station.
• To identify the hazards associated with winter storms and define the forecasting terms used to describe them.

Outline:

A. INTRODUCTION

• Practical Problems
• Historical Perspective

B. THE NORWEGIAN or POLAR FRONT (WAVE CYCLONE) MODEL

• Designation of Extratropical Cyclones
• Distinguishing Features of a Mature Polar Front Cyclone

C. OBSERVED WEATHER FEATURES SURROUNDING THE CYCLONE

• Fronts
• Pressure Fields & Pressure Tendency Fields
• Wind Fields
• Temperature Fields
• Cloud Fields
• Precipitation & Other Significant "Weather" Events

D. LIFE CYCLE OF AN EXTRATROPICAL WAVE CYCLONE -
           "THE OCCLUSION PROCESS"

• Storm Formation (or cyclogenesis)
• Early Developing Stage
• Mature Stage
• Occluding Stage
• Occluded Stage

E. OTHER FEATURES OF THE POLAR FRONT CYCLONE MODEL

• Cyclone Families
• Energetics of Cyclogenesis - The Driving Force
• Regions of Cyclogenesis
• Limitations and Complications of the Polar Front Model

F. MOVEMENTS OF EXTRATROPICAL WAVE CYCLONES

• General Movements
• Principal Cyclone Tracks over North America
• Time Sequences of Weather Events - Single Point Forecasting

G. WINTER STORMS

• Definitions
• Winter Weather Conditions
• Hazards of Winter Storms
• Ingredients of  Winter Storms
• Public Information Dissemination and Public Safety Precautions

Links to Other References:

• The Midlatitude cyclones module from Weather World 2010 (Univ. of Illinois-Urbana-Champaign).
• For Educational Resources
• Winter Storm lesson in the The Severe Weather Information Kit (SWIK) from Univ. of Nebraska at Lincoln.
• Secondary school level Weather Forecasting unit from Nebraska Earth Science Education Network (NESEN)
• Storms and storm tracks from NASA Goddard
• For advanced level

The Weather Forecasting module from Weather World 2010 (Univ. of Illinois-Urbana-Champaign).