Unit 3 Exam Study Guide Chapter 11: Air Masses and Fronts Air Masses • • • • • Definition Source regions o Where are they generally located? o What are the favorable conditions for air mass source regions? Air mass classification o Which two factors/characteristics is the classification system based on? Air mass modification Know the five air masses that commonly occur in North America o Names/abbreviations o Common locations o Typical conditions § Example: A maritime tropical (mT) air mass is warm and humid with frequent thunderstorms. It is typically located near the Gulf of Mexico and Southeast U.S. Fronts • • • • • Types of fronts (cold, warm, occluded, stationary) and their definitions Symbols/colors used to draw each type of front, and in which direction they move based on the way their symbols are drawn How to identify each type of front (i.e., wind direction shifts, temperature changes, dewpoint changes, pressure minima) Know the characteristics of frontal passages o Temperature changes o Dewpoint changes o Pressure changes o Wind direction changes o Precipitation Common precipitation phenomena that occur with each type of front o Example: Squall lines tend to occur at or ahead of cold fronts o Example: Warm fronts can be associated with sleet or freezing rain Chapter 12: Mid-latitude cyclones • Understand the definition of a mid-latitude cyclone • Know the definition of cyclogenesis • • • • • • Norwegian Cyclone/Polar Front Theory: o Steps to cyclone formation o How does this theory explain the life cycle of a cyclone? o Where is the warm sector located and why is it important? On which side of mountain ranges is cyclogenesis typically favored? Know what a nor-easter storm is. Know the definition of a “bomb” cyclone For surface cyclone intensification, understand: o The role of upper-level divergence, including in jet streaks o The relationship between the strength of upper-level-divergence and lower-level convergence o The ideal position of the upper-level trough relative to the surface cyclone For surface anticyclone intensification, understand: o The role of upper-level convergence o The relationship between the strength of upper-level-convergence and lower-level divergence o The ideal position of the upper-level ridge relative to the surface anticyclone Chapter 14: Thunderstorms and Lightning Thunderstorms • • • • • • Know the three necessary thunderstorm ingredients o Which 4th ingredient is required for severe thunderstorms? Ordinary thunderstorms: o Know the stages of development o Understand why they don’t last too long Severe thunderstorms: o Development o Structure o Why do they last longer than ordinary t-storms? o Understand what a gust front is and how it forms o Understand the key factors for hail formation Squall lines o Structure o Typical location relative to fronts Downbursts (microbursts) o Definition and impacts o Appearance o Understand the threat they post to aviation U.S. thunderstorm climatology o Where do the most thunderstorms occur in an average year? § What about those associated with dry lines? o Where do the least thunderstorms occur in an average year? Lightning • • • • • Know what causes lightning Definition of thunder and its relationship to lightning Know the location of positive and negative charges both within the cloud and on ground Formation process (stepped leader, return stroke, etc.) o Example: What do we see first with the naked eye? Types of lighting o In-cloud, cloud-to-ground, etc. Chapter 16: Tropical Cyclones (TCs) • • • • • • • • Tropical waves and disturbances: How do they form? Why do tropical cyclones not form along the equator? What is the difference between a hurricane and a typhoon? What causes tropical cyclones to move? Intensity thresholds (tropical wave/disturbance, tropical depressions, tropical storms, hurricanes) o You do not have to know the exact wind speed thresholds, except for the minimum wind speed of a hurricane o But you should know for example that tropical depressions are weaker than tropical storms and tropical storms are weaker than hurricanes TC structure and components o Eye: Lowest pressure, sinking air, partially-mostly clear skies o Eyewall: Strongest winds, rising air, powerful thunderstorms o Outer spiral bands: Heavy rain/thunderstorms, sometimes tornadoes on landfall o Outflow: Divergence of air aloft, typically anticyclonic (clockwise) o Inflow: Convergence of near-surface air TC formation, intensification and dissipation o Processes and important environmental factors (e.g., water temperature, wind shear, moisture, surface convergence) o Which factors will cause a TC to weaken? o Which environmental conditions favor TC intensification? o What are the differences between TCs and mid-latitude cyclones? TC impacts o Which quadrant of a tropical cyclone has the strongest winds and how does this vary by direction of motion? o Know the differences between a Hurricane Watch and a Hurricane Warning o Understand storm surge (what it is, what causes it)