Weather and Forecasting Flashcards
What is an extratropical cyclone.
An extratropical cyclone is a large scale weather system that forms in the mid-latitudes (30° to 60° latitude) outside the tropics. It is associated with fronts and develops due to the interaction between warm and cold air masses. These cyclones are responsible for much of the weather in temperate regions, including storms, strong winds, and precipitation.
Structure of an Extratropical Cyclone
-Low-Pressure Centre
-Frontal System (An extratropical cyclone typically has a well-defined frontal structure including a warm front, a cold front and an occlusion front.)
-Warm Sector (Region between the warm and cold fronts where warm, moist air dominates.)
-Cloud Patterns and Precipitation (Comma-Shaped Cloud Pattern.)
Occluded Front
Occluded Front:
-Forms when the cold front overtakes the warm front.
-Can produce complex weather patterns with a mix of rain, snow, and wind.
Evolution of an Extratropical Cyclone.
They develop through four stages—cyclogenesis, mature, occlusion, and dissipation.
Cyclogenesis (Formation Stage)
-Occurs along a stationary front where cold and warm air masses meet.
-A disturbance or perturbation develops, often triggered by upper-level divergence in the jet stream.
-A low-pressure system begins to form, and the rotation intensifies.
Mature (Intensification) Stage.
-The cyclone reaches its maximum strength.
-Cold and warm fronts become well-defined, and the pressure gradient increases.
-Strong winds, heavy precipitation, and active weather dominate the region.
-The warm sector becomes compressed as the cold front advances.
Occlusion Stage.
-The faster-moving cold front catches up to the warm front, forming an occluded front.
-The warm air is lifted off the ground, cutting off the cyclone’s energy source.
-Precipitation becomes widespread and intense near the occlusion.
Dissipation (Decaying Stage).
-The system loses energy as the warm air is lifted away from the surface.
-The low-pressure system weakens, and the cyclone gradually dissipates.
-This stage typically occurs over 3 to 5 days, though strong cyclones can last longer.
Rossby waves
Undulations in the jet stream.
Explain why the jet stream exists.
The existence of the jet stream is primarily due to three factors:
1) Temperature Gradient Between the Poles and the Equator
2) Coriolis Effect
3) Tropopause Boundary
How does the jet stream control the weather of the midlatitudes.
-It controls midlatitude weather by steering storms, separating air masses, and influencing temperature and precipitation patterns.
-Meandering and changes in the jet stream can lead to severe weather, blocking patterns, and persistent weather systems.
Satellite imagery.
Satellite imagery captures visual, infrared, and microwave data from space, showing cloud cover, land, oceans, and atmospheric conditions. (Space based)
Limitations: Only useful during daylight hours.
Use: Identifying cloud patterns, storm systems, and surface features.
Radar imagery.
Radar imagery uses radio waves and micro waves to detect precipitation, its intensity, and motion. (ground based)
Use: Identifying rainfall rates, storm intensity, and possible hail.
Tropical Weather Systems
ITCZ (Intertropical Convergence Zone):
-Region of rising air near the equator where trade winds from both hemispheres converge.
-Associated with heavy rainfall, thunderstorms, and tropical storms.
Hurricanes and Tropical Cyclones:
-Develop in warm tropical waters when latent heat release fuels intense convection.
-Steered by the trade winds and often curve poleward due to the Coriolis effect.
Midlatitude Weather Systems
Jet Streams and Storm Tracks:
-The polar jet stream (located at the boundary between the Ferrel and Polar cells) steers extratropical cyclones, controlling midlatitude storm tracks.
-Stronger temperature gradients in winter intensify the jet stream, leading to more powerful storms.
Extratropical Cyclones:
-Develop along the polar front where warm and cold air masses collide.
-Responsible for widespread precipitation, snowstorms, and severe weather.
Deserts and Dry Zones
Subtropical High-Pressure Zones:
-Sinking air in the subtropical highs (around 30° latitude) creates arid conditions and deserts.
-Regions such as the Sahara Desert and Atacama Desert lie under these high-pressure zones.
Polar Weather Systems
Polar Front and Polar Jet Stream:
-The boundary between polar and midlatitude air masses serves as a breeding ground for cyclonic activity.
Arctic Oscillation (AO) and Polar Vortex:
-Variability in the strength of the polar vortex can affect midlatitude weather, bringing extreme cold outbreaks or mild winters.
Stratus (low)
Appearance: Gray, uniform clouds that often cover the sky like a blanket.
Formation Environment:
Formed when cool, moist air is forced to rise gently, often in stable conditions.
Weather Associated:
Overcast skies and light precipitation (drizzle or snow).
Associated with stable weather conditions.
Stratocumulus (low)
Appearance: Low, lumpy clouds that form in rows or patches.
Formation Environment:
Forms in relatively stable air, but with some vertical motion.
Weather Associated:
Occasional light rain or drizzle.
Can indicate fair weather or show the end of a weather system.
Nimbostratus (low)
Appearance: Thick, dark, and featureless clouds that cover the sky.
Formation Environment:
Forms when moist, warm air rises and cools, causing widespread cloud cover.
Weather Associated:
Associated with steady, continuous precipitation (rain or snow).
Common during the overcast phase of warm fronts.
Altostratus (mid)
Appearance: Gray or blue-gray cloud layers that cover the sky, often appearing as a thick blanket.
Formation Environment:
Typically forms when moist air rises and cools in the mid-levels of the atmosphere, often ahead of a warm front.
Weather Associated:
Overcast skies, light precipitation like drizzle or snow can occur.
Indicates approaching weather systems, like a warm front.
Altocumulus (mid)
Appearance: White or gray clouds that form in patches, often with rounded shapes.
Formation Environment:
Forms when unstable air at mid-levels causes small cumulus clouds to form.
Weather Associated:
Fair weather but can indicate changeable weather, particularly when combined with other cloud types.
Sometimes seen ahead of cold fronts.
Cirrus (high)
Appearance: Wispy, feathery clouds high in the sky.
Formation Environment:
Cold, dry upper atmosphere.
Typically forms when air rises and cools at high altitudes.
Weather Associated:
Generally indicates fair weather but may signal that a change in weather is coming (approaching warm or occluded front).
Can indicate the approach of a storm if thickening over time.
Cirrostratus (high)
Appearance: Thin, transparent, white layer covering the sky, sometimes with a halo effect around the sun or moon.
Formation Environment:
Formed when moisture-laden air rises, cools, and condenses at high altitudes.
Weather Associated:
Fair weather but may indicate a storm front approaching.
Sometimes precedes a warm front or a midlatitude cyclone.
