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NATS 101 Lecture 23 Fronts

NATS 101 Lecture 23 Fronts. Review. Air Masses Large regions with “uniform” temperature and moisture distributions and distinctive weather Classified by Source Region Continental (c) or Maritime (m) Polar (P) or Tropical (T) Source Regions Big in area (>1600 km by 1600 km)

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NATS 101 Lecture 23 Fronts

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  1. NATS 101Lecture 23Fronts

  2. Review • Air Masses Large regions with “uniform” temperature and moisture distributions and distinctive weather • Classified by Source Region Continental (c) or Maritime (m) Polar (P) or Tropical (T) • Source Regions Big in area (>1600 km by 1600 km) Dominated by light winds (long resident times)

  3. Air Mass Characteristics Ahrens Table 8.1

  4. Air Mass Source Regions Ahrens Fig 8.2

  5. Weather Map with Air Masses, Fronts, Extratropical Cyclone Ahrens Fig 8.11 Current Weather Map

  6. Extratropical Cyclones and Fronts • In mid-latitudes, significant weather is often associated with a particular type of storm:Extratropical Cyclone • Cyclone denotes the circulation around a low pressure center • The energy for extratropical cyclones comes from horizontal temperature contrasts

  7. Extratropical Cyclones and Fronts • ET cyclones often form on a boundary between a warm and cold air mass, associated with the jet stream • They tend to focus temperature contrasts alongfrontal zones,bands of very rapid horizontal temperature changes

  8. Extratropical Cyclones and Fronts • Strongest temperature gradients occur at warm edge of frontal zone, called afront • There arefour typesof fronts Classified by their movement Each has its own symbol, color scheme Cold, Warm, Stationary,Occluded

  9. Frontal Types Cold-cold air advances, warm air retreats -10oC Homogeneous -5oC COLD 0oC 5oC Strong Thermal Contrast Surface Wind Frontal Motion WARM Homogeneous Cold Front Animation

  10. Frontal Types Warm-warm air advances, cold air retreats -10oC Homogeneous -5oC COLD 0oC 5oC Strong Thermal Contrast Surface Wind WARM Frontal Motion Homogeneous Warm Front Animation

  11. COLD -10oC -5oC 0oC 5oC WARM Frontal Types Stationary-neither air mass advances significantly Homogeneous Strong Thermal Contrast Surface Wind Frontal Motion Homogeneous

  12. Frontal Types Occluded-Looks like a hybrid between a cold and warm front, with warmest air along front -10oC Homogeneous -5oC 0oC Surface Wind COLD 5oC Strong Thermal Contrast Frontal Motion Strong Thermal Contrast COLD WARM Homogeneous Occluded Front Animation

  13. 2) Frontal Passage Pressure Trough Wind Shift Abrupt Temp Fall Rain, T-Showers 3) Post-Cold Front Temp: Rapid Cooling Press: Rapid Rising Wind: W-NW Dew Pt: Lowering Sky: Clearing Wx: Drying 1) Pre-Cold Front Temp: Warm Press: Steady/Falls Wind: S-SW Dew Pt: High Sky: Variable Wx: Showers Ahrens Fig. 8.12

  14. Cross-Section: Cold Front Cumulus-type Clouds High Clouds Ahrens Fig. 8.13 Slope = 1 in 50 Narrow band of rising warm air at cold front Widespread sinking cold air behind cold front Cold Front Animation

  15. Typical Cold Front Weather

  16. 2) Frontal Passage Pressure Trough Wind Shift Steady Warming Rain Ending 1) Pre-Warm Front Temp: Warming Press: Falling Wind: E-SE Dew Pt: Rising Sky: Lowering Ceiling Wx: Widespread Precip 3) Post-Warm Front Temp: Warm Press: Steady/Rises Wind: S-SW Dew Pt: High Sky: Variable Wx: Showers Ahrens Fig. 8.14

  17. Cross-Section: Warm Front Low Clouds-Middle Clouds-High Clouds Ahrens Fig. 8.15 Slope = 1 in 300 Widespread region of rising warm air ahead of warm front Leads to widespread region of precipitation ahead of front Warm Front Animation

  18. Typical Warm Front Weather

  19. Occluded FrontsCold-Warm Hybrid Cold Occlusion Occluded Front Animation Warm Occlusion USA Today Animation Ahrens Fig. 8.17 and 8.18

  20. Typical Occluded Front Weather

  21. Summary Fronts • ET cyclones tend to focus temperature contrasts alongfrontal zones • Strongest temperature gradients occur at warm edge of frontal zone, called afront • Fronts classified by movement, each has own symbol and characteristic weather Cold, Warm, Stationary,Occluded

  22. Summary: Frontal Weather L Temp: Slow Warming Press: Falling Wind: E-SE Dew Pt: Rising Sky: Lowering Ceiling Wx: Precipitation, Low Vis. Temp: Rapid Cooling Press: Rapid Rising Wind: W-NW Dew Pt: Lowering Sky: Clearing Wx: Improving Temp: Warm Press: Steady Wind: S-SW Dew Pt: High Sky: Variable Wx: Showers

  23. Assignment for Next Lecture • Topic -Extratropical Cyclone Formation • Reading -Ahrens pg 219-228 • Problems -8.14, 8.15, 8.17

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