This is Lab 3 of 3 in the meteorology unit. Lab 1 taught you to read a station model. Lab 2 taught you where air masses come from and how they change. Now you find out what happens when two of them collide — because the most dramatic weather in the middle latitudes does not happen inside an air mass. It happens along the sloping boundary between two of them.
Reference Table: Keep the 2024 ESRT open to the Weather Map Symbols page. The four front symbols you need are printed there and you may use them on the Regents exam.
Vocabulary Cards
Tap a card to reveal its meaning. Only one stays open at a time and each closes after 8 seconds. Open any card as often as you like.
Vocabulary Matching
Choose the correct term for each description. 1 point each
Reading — What a Front Really Is
Where two air masses of different density meet, they do not blend. The density contrast, produced mainly by temperature and secondarily by water-vapour content, keeps the two bodies of air distinct for days. The narrow transition zone between them is a front — a word borrowed deliberately from the battlefield vocabulary of the First World War by the Norwegian meteorologists Vilhelm and Jacob Bjerknes, who saw the atmosphere as opposing armies of air engaged along a moving line.
A front is never a vertical wall. Because cold air is denser, it always wedges beneath the warm air, and the boundary between them slopes upward over the cold air. The steepness of that boundary is the frontal slope, written as vertical rise over horizontal distance. Cold fronts are comparatively steep, roughly 1:75; warm fronts are far gentler, roughly 1:200. That single geometric difference explains nearly everything about the weather each front produces. A steep boundary forces air upward abruptly and builds towering cumulonimbus in a narrow band; a gentle boundary lifts air slowly across hundreds of kilometres and spreads layered stratiform cloud with long-lasting light precipitation.
The line drawn on a surface map shows only where the frontal surface meets the ground. Its symbols encode two things at once: which type of front it is, and which way it is moving. Blue triangles mark a cold front and point in the direction of movement. Red semicircles mark a warm front and bulge in the direction of movement. A stationary front carries both, on opposite sides, because neither air mass is advancing. A purple line carrying triangles and semicircles on the same side marks an occluded front.
Human impact. Frontal boundaries are public-safety boundaries. Squall lines along fast-moving cold fronts generate the damaging winds, hail and tornadoes responsible for most severe-weather deaths in the central United States each spring, and the National Weather Service can issue watches hours ahead precisely because a front’s position can be tracked. Stalled fronts train thunderstorms over one watershed and cause flash floods. Understanding fronts is not an academic exercise; it is the basis of warnings that save lives.
Figure 1. A surface weather analysis of the United States showing all four types of front at once. Gray lines are isobars labelled in millibars.
Language of Science
A. Expand the bare-bones sentence
Bare-bones sentence: The clouds thickened.
Prompt 1 — When / Where: Rewrite the sentence to tell when and where this happened relative to a warm front.
Prompt 2 — Why / How: Rewrite the sentence to explain why or how it happened, using the idea of overrunning.
Graded by Mr. Brownteacher graded
B. Sentence Scrambler
Tap the words in order to rebuild the sentence. Correct words turn green. 1 point
Tap a word in your sentence to send it back to the word bank.
Page 2 of 5 · about 9 minutes
Cross Sections of the Four Fronts
A map is a view from straight above. It tells you where a front is but almost nothing about how it works. For that you need a cross section — a slice through the atmosphere, as if you cut it open along a line and looked at the exposed face. Distance runs along the bottom; altitude runs up the side. Because the vertical axis is stretched enormously, every frontal surface below looks far steeper than it truly is. A real cold front rising one kilometre over seventy-five kilometres of ground would look almost flat if drawn to true scale.
Figure 2. Cold front. Warm air is forced up along the steep frontal surface, so the cumulonimbus and the narrow band of heavy rain sit behind the surface position of the front.
Figure 3. Warm front. The gentle 1:200 slope spreads cloud and light precipitation over a band 300 to 500 km wide, well ahead of the surface front.
Figure 4. Stationary front. The opposing forces are balanced, so the boundary does not advance and the same area receives rain for days.
Figure 5. Occluded front. The coldest air undercuts the cool air and lifts the warm air completely off the ground. Its lowest point, the triple point, sits about 4 km up.
⏯ Simulation — Frontal Passage Walk-Through
Choose a front type, then advance time. The front sweeps from west to east past a fixed weather station while the instruments update. Use the numbered Stop buttons to collect your data.
Air Temp
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Dew Point
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Pressure
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Wind
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Clouds
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Precip
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Move the slider to begin.
Data Table 1 — Cold Front Passage
With Cold Front selected, go to Stop 1, press Record This Reading, then repeat through Stop 5. After each reading decide where the station is relative to the front. 4 points for a completed table
Stop
Air Temp
Dew Point
Air Pressure
Wind
Precipitation
Where Is the Station?
1
2
3
4
5
Before you leave this page, switch the simulation to Warm Front and walk through its five stops too. Questions 11 and 12 ask what you saw.
Page 3 of 5 · about 7 minutes
Questions
Quick reference: cold front = blue triangles, steep 1:75, rain at and behind the boundary · warm front = red semicircles, gentle 1:200, wide rain band ahead · stationary = both symbols on opposite sides · occluded = purple, both symbols on the same side, warm air lifted off the ground.
SRA student claims: “At an occluded front the warm air mass is still in contact with Earth’s surface, just as it is at a cold front.” Choose Support or Refute, then justify your answer. 1 pt + 2 written
Justification — use evidence from Figure 2 and Figure 5:
The justification is graded by Mr. Brownteacher graded
Page 4 of 5
Mastery Quiz
Regents-Style Mastery Check
5 questions are drawn at random from a bank of 20. You need 60% or higher to reach mastery. If you fall short you may retry with a fresh set.
Attempt 1
0 / 5
Page 5 of 5
Final Grade & Print to PDF
Auto-Scored Grade
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0%
0 of 0 auto-scored points
Turn In Your Work
Press the button below to build a printable report with your student ID, your grade, your data table, your graphs and diagrams, and every question with your answer. Choose Save as PDF as the destination, then submit the PDF to Mr. Brown.
