Chapters 9, 10 and 11. Exam during your scheduled class time. Questions? Email Professor Hoffman.
The original course notes state that a missed exam is replaced by the final exam grade; confirm details in the current course syllabus.
Midlatitude Cyclones and Weather Patterns
Midlatitude cyclones are large low-pressure systems, often over 600 miles (1,000 km) across, that commonly travel west to east in the prevailing westerlies. In the Northern Hemisphere, winds circulate counterclockwise and inward around the surface low. A cold front and often a warm front extend from the low-pressure center.
Chapter 9 Class Videos
Chapter 9 — Part 1
Chapter 9 — Part 2
Fronts and Air Masses — Video 1
Fronts and Air Masses — Video 2
Fronts and Air Masses — Video 3
Fronts and Air Masses — Video 4
Five Types of Fronts and Boundaries
Fronts separate air masses with different temperature and density. The surface weather can change rapidly as a boundary passes.
Cold Front
Advancing colder, denser air pushes beneath warmer air. A band of showers or thunderstorms may develop. Winds often shift and temperatures fall after passage.
Warm Front
Advancing warm air rises over retreating colder air. Clouds often lower and thicken ahead of the front, with widespread precipitation possible.
Stationary Front
A boundary with little movement. Clouds and precipitation may persist near it.
Occluded Front
A faster cold front catches a warm front and lifts the warm air away from the surface. Cold-type and warm-type occlusions depend on the relative temperatures of the surrounding air.
Dryline
A sharp boundary between humid and much drier air, common in the Plains. It can help trigger severe thunderstorms when other ingredients are present.
Weather Before, During and After a Front
Cold Front — Typical Changes
| Element | Before | During Passage | After |
|---|---|---|---|
| Winds | South to southwest | Gusty and shifting | West to northwest |
| Temperature | Warm | Often drops sharply | Cooler |
| Pressure | Falling | Near minimum, then rising | Rising |
| Clouds | Increasing clouds | Often cumulonimbus | Cumulus, then clearing |
| Precipitation | Possible showers | Showers or thunderstorms; sometimes heavy | Showers ending |
| Dew Point | Often higher | May drop | Usually lower |
Warm Front — Typical Changes
| Element | Before | During Passage | After |
|---|---|---|---|
| Winds | Often easterly or southeasterly | Variable or shifting | Often southerly |
| Temperature | Cool | Rising | Warmer |
| Pressure | Falling | Leveling off | Variable |
| Clouds | Cirrus → cirrostratus → altostratus → nimbostratus | Low clouds possible | May break up |
| Precipitation | Widespread rain or wintry precipitation possible | Drizzle or light precipitation possible | Often ending |
| Dew Point | Often rising | Higher | Typically more humid |
These are typical patterns, not guarantees. Actual wind shifts, cloud types and precipitation depend on the storm track, season and atmospheric profile.
Life Cycle of a Midlatitude Cyclone
In the Norwegian cyclone model, a disturbance develops along a frontal boundary. A wave and surface low form; warm air moves poleward while cold air advances equatorward. The cold front often catches the warm front, creating an occlusion. As the temperature contrast and upper-level support diminish, the system generally weakens.
Upper-Level Support
When divergence aloft removes air from the column faster than low-level convergence replaces it, surface pressure can fall and the cyclone can intensify. When this balance reverses, surface pressure may rise and the cyclone can weaken.
Textbook focus: Pages 241–243, including how cloud cover, wind, temperature, precipitation and pressure change as a storm moves past a location.
Analyze Current Weather Maps
Practice locating low-pressure centers, frontal boundaries, wind shifts and precipitation areas. These links open current operational charts rather than relying on older embedded graphics that may no longer load.
WPC Surface Analysis
WPC National Forecast Charts
NWS New York Forecast Office
WPC Precipitation Forecasts
PowerPoint Presentations and Diagrams
Fronts
Open PowerPointClouds and Precipitation
Open PowerPointFour Ways Air Rises
Open PowerPointChapter 9 Fronts
Open PowerPointAdditional station-plot and weather-symbol material appeared below the original “STOP HERE FOR TEST 4” line and is therefore not included in the required exam review. For enrichment, use WPC station plot explanations.
Test 4 — Chapter 9 Review
Wednesday, December 9, 2026 • Chapters 9, 10 and 11
- Identify cold, warm, stationary and occluded fronts and drylines by their symbols and definitions.
- Describe wind direction, pressure trend, temperature, dew point, clouds and precipitation before and after frontal passage.
- Explain the relationship between frontal lifting and precipitation.
- Recognize the warm sector and the cold and warm fronts on a surface map.
- Explain the stages of the midlatitude cyclone life cycle and the role of divergence aloft.
- Interpret a storm's position relative to Long Island to anticipate weather changes.