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Difficulty: HardAtmosphere and Weather

During a meteorological observation in the mid-latitudes of the Northern Hemisphere, an observer records a rapid drop in barometric pressure followed by the development of towering cumulonimbus clouds and intense localized thunderstorms. Immediately after the storm passes, the barometric pressure rises sharply, ambient air temperature plummets, and surface winds abruptly veer from south-southwest to northwest. Which of the following meteorological events is directly responsible for this observed sequence of weather changes?

  1. A
    The establishment of a stationary high-pressure anticyclone with subsiding, divergent air flow
  2. The passage of an active cold front rapidly displacing and uplifting a warm, humid air massAnswer
  3. C
    The gradual advance of a warm front overriding a retreating wedge of cooler air
  4. D
    The formation of a nighttime surface thermal inversion trapping saturated air through accelerated evaporation

Answer

The passage of an active cold front rapidly displacing and uplifting a warm, humid air mass
The passage of an active cold front is characterized by dense, cold air aggressively wedging under warmer, less dense air along a steep boundary. This rapid vertical displacement creates a low-pressure trough, fuels convective cumulonimbus storms, and produces an abrupt post-frontal transition featuring rising barometric pressure, colder temperatures, and a typical clockwise wind shift toward the northwest in the Northern Hemisphere.

Step-by-Step Solution

1
Analyze the pre-frontal atmospheric indicators described in the scenario
Falling barometric pressure, warm south-southwesterly flow, and explosive cumulonimbus cloud growth indicate rapid vertical forcing of unstable, humid air.
Cold fronts possess steep frontal slopes (roughly 1:50 to 1:100) that aggressively wedge beneath warm, moist air, triggering severe convection.
2
Evaluate the post-frontal thermodynamic and kinematic changes
A sharp rise in pressure, plummeting temperatures, and a distinct wind shift from south-southwest to northwest confirm the arrival of a polar or arctic air mass behind a cold front in the Northern Hemisphere.
As the surface low-pressure trough passes and the denser cold air mass moves in, pressure rebounds and clockwise wind veering occurs due to cyclonic wind field dynamics.

Key Concept

Frontal Dynamics and Air Mass Displacements
Estimated Time:1m 30s
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Topics

Atmosphere and Weather

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