1. Severe Weather
Chapter 24 Sec. 2

2. High and Low Pressure Centers
In a High Pressure center the air sinks. Because of the high pressure the air can not rise and condense so there are usually no clouds and dry air.
In a Low Pressure center the air rises and cools. Eventually the water vapor condenses forming clouds and precipitation.

3. Fronts
Can you label the different parts of this meteorological map?

4. Severe Weather!!!!!
Ok so all these low pressure and high pressure centers mean what?
Well if conditions are right you can have severe weather systems like thunderstorms, tornadoes, and Hurricanes!
A system is categorized as severe when it brings strong winds and heavy precipitation..

5. Thunderstorms
Thunderstorms develop along cold fronts where air is forced rapidly upward causing water droplets to form.
As these large droplets fall they created a down draft which is the strong winds associated with thunderstorms. Dangerous hail can also form.
Lightning and thunder are also related in thunderstorms. Where air uplifts rapidly, electric charges form. Lightning is the almost instantaneous energy flow that occurs between areas of opposite electrical charge.

6. Tornadoes
Tornadoes also form along fontal boundaries. If conditions are just right, updrafts of rising air can start to spin into a rotating vortex. This crates a funnel cloud.
If it reaches Earth’s surface it is called a tornado. They are violent and extremely destructive. The area in central United States is called Tornado alley because of the frequent recurrences of tornadoes.

8. How do tornadoes form? Most tornadoes form from thunderstorms
You need warm, moist air from the Gulf of Mexico and cold, dry air from Canada
When these two air masses meet – this creates instability in the atmosphere

9. Continued A change in wind direction and…
An increase in wind speed (with increasing height, create an invisible, horizontal spinning effect
Then rising air within the updraft tilts the moving (rotating) air from horizontal to vertical
This take up most of the thunderstorm

10. Tornado Condition Model

11. Funnel Cloud Most of us think that a funnel cloud is a tornado…NOT SO!
A funnel cloud is a rotating cone-shaped column of air extending downward from the base of a thunderstorm, but not touching the ground.
It’s only a tornado when it touches the ground!!!!

12. Tornado Model

13. Water Spouts!
A waterspout is just a weak tornado that forms over water. They are most common along the Gulf Coast. Waterspouts can sometimes move inland, becoming tornadoes causing damage and injuries.

14. Tornado Alley!
The geography of the central part of the United States is suited to bring all of the ingredients together to forms tornadoes.
More than 500 tornadoes typically occur in this area every year and is why it is commonly known as "Tornado Alley".

15. Tornado Alley

16. Fujita Scale of Tornado Intensity
F0  40-72 mph Light damage: Branches broken off trees; minor roof damage
F mph Moderate damage: Trees snapped; mobile home pushed off foundations; roofs damaged
F mph Considerable damage: Mobile homes demolished; trees uprooted; strong built homes unroofed
F mph Severe damage: Trains overturned; cars lifted off the ground; strong built homes have outside walls blown away
F mph Devastating damage: Houses leveled leaving piles of debris; cars thrown 300 yards or more in the air
F mph Incredible damage: Strongly built homes completely blown away; automobile-sized missiles generated EF5 over 200 mph

17. Tornadoes in action
Tornado

18. Hurricanes Review
A Hurricane is a large storm that begins as an area of low pressure over tropical oceans.
The Coriolis effect causes winds to rotate counter clockwise around the center of the storm.
As the storm moves it pulls in moisture.

19. Saffir-Simpson Hurricane Scale
Hurricanes are measured using the Saffir-Simpson scale. It gives the hurricanes a rating of 1-5 depending on intensity.
They measure the winds, wind gusts, and storm surge (size of waves)
Saffir-Simpson Hurricane Scale
Category
Wind speed
Storm surge
mph (km/h)
ft (m) 5
≥156 (≥250)
>18 (>5.5) 4
131–155 (210–249)
13–18 (4.0–5.5) 3
111–130 (178–209)
9–12 (2.7–3.7) 2
96–110 (154–177)
6–8 (1.8–2.4) 1
74–95 (119–153)
4–5 (1.2–1.5)
Additional classifications
Tropical storm
39–73 (63–117)
0–3 (0–0.9)
Tropical depression
0–38 (0–62)
0 (0

20. Floods!
- A flood results from many days of heavy rain, melting snows, or when rivers rise and go over their banks

21. Flash Floods
Is sudden flooding that occurs when floodwaters rise rapidly, with no warning, after many hours of heavy rains
Flash floods are the #1 weather-related killer in the U.S.
80% of flash floods deaths occur in cars
We can protect ourselves by knowing if we live in a flood zone!
A car can float away in just 2 ft. of water!!!

22. Flood Lingo
FLOOD WATCH - means that an overflow of water from a river is possible for your area.
FLASH FLOOD WATCH - means that flash flooding is possible in or close to the watch area. Flash Flood Watches can be put into effect for as long as 12 hours, while heavy rains move into and across the area.
FLOOD WARNING - means flooding conditions are actually occurring in the warning area.
FLASH FLOOD WARNING - means that flash flooding is actually occurring in the warning area. A warning can also be issued as a result of torrential rains, a dam failure or snow thaw.

23. Flash Floods

24. Flash Flooding
Flash Flood in Action

25. Flood Safety
DURING A FLOOD: Move to a safe area quickly. Move to higher ground, like the highest floor of your home. Avoid areas subject to sudden flooding like low spots and canyons. Avoid already flooded areas. If a flowing stream of water is above your ankles stop, turn around and go the other way. Do not attempt to drive through a flooded road. The depth of the water is not obvious and the road may be washed away. If your car stalls, leave it and seek higher ground. Rapidly rising water may engulf the car, pick it up and sweep it away. Kids should never play around high water, storm drains or viaducts. Be cautious at night, because its harder to see flood dangers. If told to evacuate, do so immediately.