PHSC 3033: Meteorology Thunderstorms Air Mass Thunderstorms

• Conditional Instability • Minimal (no) vertical wind shear. • Warm, moist air.

• Localized source of lift, usually thermally driven (convective), but can be due to topography. Air Mass Thunderstorm Cross Sections Life Cycle Air Mass Thunderstorm Cold Pool Outflow Mammatus The mammatus clouds are pouch-like structures and are a rare example of clouds developing as a result of sinking motions.

They form underneath a thunderstorm where cooler air sinks into warmer air below the storm cloud.

Mammatus clouds look threatening, but actually signal the weakening In an air-mass thunderstorm.

Figure 18.11 Mesoscale Convective System Gust Front Gust Front and Inflow MESO-scale Convective System (MCS)

Figures 18.4-5 Figure 18.6 (match to 18.5 panels) Derecho Winds 2012 June 29 Derecho Event http://www.crh.noaa.gov/iwx/?n=june_29_derecho Figure 18.8: Bow Echo: Squall Line straight-line winds, weak tornados Figure 18 A: MCS bow echos Figure 18.9: MCS Squall Line Cross Section Figure 18 B: MCS: Cross Section Arcus “Roll or Shelf” Cloud Ahead of Squall Line Figure 18.7: Gust front shelf cloud

Figure 18.13: Frontal Squall Line Figure 18.12: Frontal Squall Line Frontal Squall Line Passage • Winds are warm and brisk out of the south. • As the squall line approaches, low clouds that often take on a roll-like shape (arcus clouds) approach from the west. • Just before the clouds move overhead, the wind direction abruptly shifts to the west and the temperature begins to fall. Straight-line winds are strong and common. • Rapidly behind the wind shift, the underside of the arcus cloud looks like it is “boiling” or rolling. The wind increases and the the temperature falls. A curtain of rain appears to the west. • Heavy rain follows shortly. Rain rates can be momentarily as high as 10 - 15 inches per hour. However, the rain lasts only for a short duration. Figure 18.14: Frontal Squall Line Anatomy Frontal Squall Line Figure 18.15: Frontal Squall Line Cross Section Figure 18.10: Squall Line Profile Thunderstorms in Motion http://www.youtube.com/watch?v=CV6b-uBpufM Shelf Cloud http://www.youtube.com/watch?v=6lkRvB2OGvE Shelf Cloud http://www.youtube.com/watch?v=RJNFWUzTGQY Shelf Cloud http://www.youtube.com/watch?v=DneoUJu-biw Thunderstorms http://www.youtube.com/watch?v=QpriSb6uN4A Convection http://www.youtube.com/watch?v=RqqCESro-rc Gust Front http://www.youtube.com/watch?v=SuyYAGVwoEU Squall Line http://www.youtube.com/watch?v=D9vDCR_j2xc Derecho http://www.youtube.com/watch?v=v369MNjw2Sk Thunderstorms