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STORMS AND SEVERE WEATHER. STORM: violent or severe disturbance of the atmosphere that usually creates dangerous, destructive, or unpleasant conditions on Earths surface. Storms and Severe Weather. Most storms are associated with: High winds Heavy precipitation Fronts - PowerPoint PPT Presentation

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STORMS AND SEVERE WEATHERSTORM: violent or severe disturbance of the atmosphere that usually creates dangerous, destructive, or unpleasant conditions on Earths surface.Storms and Severe WeatherMost storms are associated with:High windsHeavy precipitationFrontsLow air pressure of cyclonic conditionsPeople need to be aware that storms can:Cause loss of lifeInjuriesLoss of propertyMid-latitude or Cyclonic StormsCaused by movement of air masses along polar fronts of the middle latitudesResults in: formation of low pressure storm systems (mid-latitude cyclones)Often associated with many thunderstorms and associated hail and tornadoes.HURRICANESAn Intense low pressure system that starts as a tropical low.Winds sustained at 74 mi/hr (120 km/hr)Storm surge causes most of the damage.Energy from latent heat released during condensation fuels the stormSpin due to the Coriolis EffectCharacterized by rotating bands of precipitating clouds.Lowest pressure is in the center of the storm (cloudless eye)4When a tropical low pressure center gains enough energy and a large enough pressure gradient to sustain winds of 74 miles per hour or more, it is called a hurricane.Hurricanes have different names in different parts of the world. Once a hurricane has reached a category 5 (155 mph), the name is retired. Hurricanes continued.High winds can get to over 150 mi/hrWhen a hurricane passes over land or cold ocean water, it loses its energy source of evaporating water and slowly dissipates.Greatest threat is when a hurricane hits land.In the U.S. the southern and eastern coasts are most vulnerable.Hurricane Formation

Read, go over, and understand the 5 steps of Hurricane Formation.6

7Simple weather map and satellite image of Atlantic hurricanes. Note the bands of heavy precipitation and the clear hurricane eye. Saffir-Simpson ScaleCategorizes hurricanes

8Know the name, you do not need to know the details re numbers, just > 155 mph is catastrophic.THUNDERSTORMSThey are heavy rainstorms accompanied by thunder and lightning from Cumulonimbus cloudsA line of thunderstorms is called a squall

Thunderstorm lifecycleThe typical lifecycle of a thunderstorm consists of three stages: towering, mature cumulus, and dissipating stage

Towering cumulus cloud indicates lifting air.

Little if any rain

Lasts about 10 minutes.Occasional lightning

10Such lifting may be due to the converging air associated with anomaly heating of the ground, or due to the upstream terrain Occasional lightning will occur at this stage.

Mature Stage The air continues to rise up to the tropopause, forcing the air to be spread out.

Hail, heavy rain, lightning, strong winds likely.Lasts an average of 10 to 20 minutes .

11Dissipating Stage

Thunderstorm dissipates and is dominated by a downdraft. Rainfall decreases in intensity.

Three important ingredients:MoistureInstabilityLifting mechanism12Thunderstorm hazards Thunderstorms can create many hazards including flooding, hail, high winds, and lightning.In many years, more people get killed from lightning than any other weather-related cause.

13Hail Formation

14Note the hail growth rings. Hail isproduced by strong updrafts, which carry the raindrops continuously back into the cloud.TORNADOESMost violent of all storms.By definition, a tornado is a rapidly rotating extremely low pressure funnel that hangs down from a column of air extending from a thunderstorm to the ground.

Tornado characteristics

Wind speeds 40mph to 110mph

Often travel a few miles before dissipating. Rotate counterclockwise in NH. Opposite in SH17Radius: Some stretch more than a mile across, and stay on the ground for dozens of miles.[Some attain wind speeds of more than 300mph (480km/h),

Tornado formation

Before thunderstorms develop, vertical wind shear creates an invisible, horizontal spinning effect in the lower atmosphereUpdraft within the thunderstorm tilts the rotating tube from horizontal to vertical.An area of rotation of few miles wide is formed within the storm. Most tornadoes form within this area of strong rotationAn area of rotation of few miles wide (mesocyclone) is formed within the storm18Tornado scales

19The Fujita (F) Scale is the most commonly used scale for rating the damage of tornadoes, which is based on damage left behind by a tornado. There are some disadvantages of the F scale, and a recently revised scale, so-called Enhanced Fujita (EF) Scale seem to make improvements to the original F scale. This EF Scale has replaced the original F scale, which has been used to assign tornado ratings since 1971.

Types of Tornadoes

Waterspout and landspout20

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