Chapter 19: Weather Patterns and Severe Storms Flashcards
What are the characteristics of air masses?
- Large body of air (several km thick)
* Similar Temperature and Moisture level @ any given altitude
What is a cold Canadian air mass?
The air mass becomes warmer, but also brings some of the coldest weather of the winter.
Comes from the south
What is the area where an air mass acquires its properties?
Source Region
Two parts of criteria that is used to classify air masses?
1) Latitude of the source region.
Polar- high lat. cold
Topical– low lat. warm
2) Nature id the surface in the source region
Continental- air mass forms over land (dry)
Maritime
The five basic types of air masses
1) Continental Polar (cP): dry/cold
2) Continental Arctic (cA): dry/ very cold (winter only)
3) Continental Tropical (cT): dry/warm (summer only)
4) Maritime Polar (mP): humid/cold
5) Maritime Tropical (mT): humid warm
The most important air masses in North America
cP and mT and are most commonly in the east Rockies
What act as boundaries that separate air masses of different densities?
Fronts
What are some identities of air masses?
- One air mass is usually warmer than one that contains moisture.
- The warmer, less dense air is forced aloft (up).
- Cooler, denser air acts as a wedge as it stay low.
- Fronts are relativity narrow.
Two types of Fronts
- Warm Fronts
2. Cold Fronts
What is a Warm Front?
- warm air replaces cooler air
- on weather map is seen w/ semi-circles
- slow rate of advance
- low clouds
- light-moderate precipitation
What is a Cold Front?
- cold air replaces warm air
- on weather map is seen w/ triangles
- twice as steep as a warm front
- advances faster than a warm front
- associated weather is more violent than warm front: intensity of prec. greater… duration of prec. shorter
What is a Stationary front?
A flow of air on both sides of the front is almost parallel to line of front.
Surface position does not move.
What is a Occluded Front?
Active cold front overtakes a warm front.
Precipitation is associated w/ warm air being forced aloft
The life cycle of a middle-latitude cyclone?
Form along front where air masses are moving parallel to the front in opposite directions.
Continental polar (cP) n: north front Maritime tropical (mT): south front
The overtaking of one front by another, is called what?
Occlusion
A storm that generates lightning and the resultant thunder, is called what?
A Thunderstorm!
Features of a Thundestrom
- Cumulonimbus clouds (vertical)
- Heavy rainfall
- Lightning and thunder
- Gusty winds, occasional hail
What is the occurrence of a thunderstorm?
45,000 thunderstorms per day.
100,000 thunderstorms per year
Most frequent in Florida and eastern gulf coast. AKA THY’RE COMMON
Stages of development of a Thunderstorm?
1) require continuous supply of warm air & moisture or storm will dissipate
- surge causes air to rise higher
- updrafts (warm) and downdrafts (cool)
2) Eventually precipitation forms
- most active stage of storm
- gusty winds , lighting, hail
- heavy precipitation
3) Cooling effect of precipitation
- marks the end of the thunderstorm activity
For a thunderstorm to occur what does it require?
- Warm air
- Moist air
- Instability (lifting)
Most common in the afternoon and early evening b/c that’s when air is warmest
Local, Violent & destructive wind storm of a short duration, is called what?
A Tornado
Features of a Tornado
- Rotating column of air that extends down from a cumulonimbus cloud
- Very low pressure inside storm causes air rush into tornado
- Suction vortices can form inside - this is hwy certain ares are destroyed in storm path & others are not touched at all.
How often do Tornado’s occur and how they develop?
- Average of 770 tornadoes each year in US
- Most frequent April- June
- No one knows the exact reasons they form.
- Strong updrafts in a thunderstorm & winds in the troposphere
What kinds of conditions do you need for a tornado to occur?
- Spring months occurred most
- Associated w/ huge thunderstorms called Supercells
- Can occur in any sever weather situation
A vertical cylinder of rotating air, typically 2-6 miles across, is called what?
A Mesocyclone
When winds aloft are moving much faster than those near the surface that produces rolling motions across the horizontal axis, is called what?
Speed Wind Sheer
What are the characteristics of a Tornado?
- Diameter between 500-2,000 ft
- Moves across land @ 30 mph
- Cuts about 6 mile long path on average
- Maximum winds of 310 mph
- Intensity measured by Enhanced Fujita Intensity Scale
What is the Enhanced Fujita Intensity Scale (EF)?
A 6-category scale that represents the increasing degrees of damage during a tornado.
Revised in 2007.
What is a Tornado Watch?
To alert the public to the possibility of tornadoes.
Issued when the conditions are favorable..
What is a Tornado Warning?
Issued when a tornado is sighted on the ground by the weather radar.
What is a Tornado Emergency?
The most severe warning.
Must seek shelter underground to survive.
What is a Hurricane?
The most violent storms of Earth!!!
Wind speeds excess of >74 mph
Rotary cyclone circulation
Different names for Hurricanes and where to find them?
- Typhoon- western Pacific, Japan, and Southeast Asia
- Cyclones- Indian Ocean
- Hurricanes- Gulf of Mexico ,North Atlantic Ocean, Eastern Pacific Ocean.
What is the eye of a hurricane?
- The very center of the storm
- precipitation ceases in the eye
- warmest part of storm
- air descends
What is the eye wall?
- Wall of cumulonimbus clouds @ center of storm
- Greatest wind speeds are here
- Heaviest rainfall happens here
When winds do not exceed 38 mph, this is called what?
A Tropical Depression
When winds reach between 38-74 mph , this is called what?
A Tropical Storm
When do Hurricanes occur?
- They form in tropical waters
- Comes from condescending water vapor
- Most often happen in late summer
When do hurricanes diminish their intensity?
- They move over cooler water
- They move onto land
- They large-scale flow aloft is unfavorable to continue to support the storm
The Saffir-Simpson Scale?
Ranks the relative intensities of hurricanes based on
- wind speed
- pressure
- storm surge
(Has five levels to it.)
Three factors that affect the amount of damage from a hurricane?
- Strength of storm- (most important)
- Size & population density of are affected
- Shape of the ocean bottom near the shore
Three categories of hurricane damage?
- Storm Surge- large dome of water that sweeps across coast where eye of storm makes landfall. (40-50 miles wide)
- Wind damage
- Inland flooding from torrential rains
2017 Hurricane Harvey
- Category 4- 130 mph winds
- 82 fatalities
- $190 -$200 billion in damages
- Flooding was between 04-60 inches of rainfall on Aug. 24 -Sept. 1 in southern Texas.
- Slow moving
2017 Hurricane Irma
- Category 6- 185 mph winds
- 134 fatalities
- $80 -$100 billion in damages
- Struck Florida on & moved inland on Sept. 9-10th.
- Strongest storm observed in Atlantic since 2005.
