TOPICS: What are Thunderstorms? Ingredients Stages Types Lightning Downburst and Microburst

Transcription

1 THUNDERSTORMS

2 TOPICS: What are Thunderstorms? Ingredients Stages Types Lightning Downburst and Microburst

3 What are Thunderstorms? A storm produced by a cumulonimbus cloud that contains lightning and thunder

4 Convective Ingredients Instability Moisture Lift Exhaust All of these must be present for thunderstorms to occur

5 Instability A condition of the atmosphere where by a parcel of air, given an initial start vertically, then continues to move upward without any outside force. Instability can be caused by: Surface heating Cooling aloft Evaporational cooling Dry air is advected into a moist area

6 Moisture Necessary for cloud formation Increasing moisture will enhance instability

7 Lift (trigger) Force needed to get a parcel of air to it s Level of Free Convection The three main triggers Boundaries Fronts, troughs, outflow boundaries and moist discontinuities (dry-lines) Topography Mountains and coastlines Differential heating Strong temperature gradient over a short distance

8 Exhaust Upper level divergence is required

9 Evolution of Thunderstorm Development Cumulus Stage Mature Stage Dissipating Stage

10 Cumulus Stage Begins with the formation of the first convective cloud Dominated by updrafts Updrafts hold the prospective precipitation aloft

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12 Mature Stage Cloud particles grow too large for the rising air to keep them suspended The particles then fall against the updraft and create a downdraft The cloud reaches the stratosphere and the top begins to spread out Most violent and active stage Thunder and lightning begin in this stage The heavier the precipitation the stronger the downdraft

13 Mature cont. Updrafts and downdrafts reach their greatest strength in the middle of the cloud, creating severe turbulence Ice crystals suspended near the melting level alternate between freezing and melting, producing hail Hailstones continue to grow until it is too heavy to be supported by the updraft core Aircraft have encountered hail in clear air several kilometers away from the storm

14 Mature cont. The leading edge of the downdraft at the surface is known as the gust front or outflow boundary The gust front produces Low-Level Wind Shear

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16 Dissipating Stage Begins when the updraft collapses and the downdraft dominates The downdraft cuts off the inflow of warm, moist air into the storm Cloud droplets stop forming The cloud begins to stratify into layered clouds

17 Types of Thunderstorms Single cell Multi-cell Supercell Thunderstorms Squall line

18 Single Cell Thunderstorms Air mass thunderstorms Short lived (30 to 60 minutes) Severe weather is rare

19 Multi-cell Thunderstorms Requires a greater degree of instability Strong mid level winds carry the precipitation downstream so it doesn t fall into the updraft New cells continue to form on the right flank and develop into mature storms Storms last longer due to their ability to renew themselves

20 Supercell Thunderstorms Updrafts and downdrafts are so sufficiently in balance that it can maintain itself for hours on end Producers of tornadoes and destructive hail

21 Squall Line A line of thunderstorms that is not readily circumnavigable Normally occur 50 to 300 miles ahead of a cold front Produce high winds Hail and tornadoes are possible

22 Lightning A discharge of electricity which occurs during the mature stage of thunderstorms Types of lightning In cloud Cloud to cloud Cloud to air Cloud to ground

23 Lightning hazards Flash blindness Puncture aircraft skin Shock and burns Fuel ignition Damage to equipment

24 Downburst Strong concentrated downdraft with a great potential for damaging surface winds Usually located behind the gust front Wind speeds are greater than 40 knots at the surface

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26 Microburst Concentrated downburst 4 kilometers or less Change in velocity of 50 knots or greater

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28 Questions?