1) Atmospheric pressure is caused by differences in air density, which is influenced by differential heating from the sun. This causes global wind patterns and pressure cells. 2) Differential heating also causes regional weather phenomena like thunderstorms and tornadoes as warm air rises and cold air sinks, interacting with pressure systems. 3) Various technologies like Doppler radar, weather watch programs, and storm research vehicles help provide early warnings of severe weather to help mitigate damage and save lives.

1. Inland Storms

2. Atmospheric (barometric) Pressure
Atmospheric pressure is the weight of a column of of air over a given point.

3. Wind
Wind is caused by differences in atmospheric pressure, as air flows from areas where the
atmosphere is thicker (high P) to those where it’s thinner (low P). Pressure gradients are
caused mostly by differential heating of the earth’s atmosphere and surface.

4. Pressure Cells
Thick masses of dry air move downward in high pressure cells and
expand outward. Air converges inward toward the center of low pressure
cells and then rises, condensing to form clouds.

5. Global Differential Heating
Because of earth’s spheroidal shape, a given amount of solar energy will
is spread over a larger area at the poles than along the equator.

6. Atmospheric Convection
Differential
heating of the
earth’s surface
results in large-scale
atmospheric
convection cells
that stretch from
the equator to the
poles and back.

7. Coriolis Effect
Because of earth’s
rotation, atmospheric
and oceanic currents are
deflected clockwise in
the northern hemisphere
and counter-clockwise in
the southern, giving
these currents a curved
path. There is no
deflection at the equator.

8. Prevailing Wind Patterns
A combination of differential heating and the Coriolis Effect produce
global-scale prevailing wind patterns.

9. Global Pressure Cells
Disruption of prevailing wind patterns by continental masses leads to the
formation of pressure cells, which play a major role in global and
regional weather patterns.

10. Regional Differential Heating
(altitude)
During the day, atmospheric molecules are heated, lowering their density
and causing them to rise. At night time, these particles cool, increase in
density, and descend.

11. Regional Differential Heating
(surface materials)
Different surface materials, such as
land and sea or land and ice, have
different capabilities of absorbing
and retaining heat, leading to lateral
changes in air density.

12. Fronts
Cold front: cold air advances
toward warm air, forcing the
warm air to rise.
Warm front: warm air
advances toward cool air and
rises over cold mass.
Stationary front: little
movement between air masses.
A front is the boundary between air masses of different densities, usually cool and warm.

13. Thunder Storms

14. Thunder Storm Structure
Thunderstorms form as warm, moist air rises rapidly, passes over cold
air, and cools at higher altitudes, producing clouds and precipitation.
They occur most commonly during the afternoon and evening hours of
spring and summer.

15. Photo by W. W. Little

18. Rain forms from either the melting of ice crystals and snowflakes falling
from higher altitudes or from the coalescence of smaller water droplets.

19. http://img139.imageshack.us
Hail
http://www.rapiddent.com.au/images/HailFormation.jpg NOAA
Hail is produced as ice passes up and down within a cloud. At lower
levels it becomes coated with water that freezes when taken to higher
altitudes, forming concentric rings.

21. Lightning
Lightning is a flash of light that occurs as electricity is discharged from
electrically-charged clouds. Surrounding air can be heated to 30 K0 C,
5X the temperature of the Sun’s surface. Rapid expansion of
surrounding air produces thunder.

22. Clouds become electrically charged as
ice crystals move vertically past one
another. A negative charge at the
cloud base drives away negative
particles at the ground surface and
draws positive particles upward.

23. About 80% of lightning occurs between clouds.

24. Thunderstorm Occurrence
In the U.S., thunderstorms are most common along the Gulf Coast,
followed by the Front Range of Colorado and New Mexico. Globally,
Uganda has the record with a storm 7 out of every 10 days.

25. Tornadoes
Tornadoes form as part of supercell thunderstorms as the warm updraft
produces a powerful vortex.

27. Tornado Development
Tornadoes form as irregularities along a major front (boundary between cold
and warm air masses) allow rotation to begin as warm air rises and cold air
descends, forming a vortex. The vortex becomes visible as moisture
condensates or it gathers dust.

29. Tornado Outbursts

34. Tornado Stages
Wall Cloud Funnel Cloud
Mature Waning

36. Tornado Occurrence
http://www.nssl.noaa.gov/primer/tornado/images
Tornadoes occur worldwide and have been reported from all fifty states.
However, by far the most common occurrence globally is in “Tornado Alley”
of the United States. This is due to a unique set of weather conditions that lead
to regular mixing of cold and warm air masses, along with an abundant
moisture supply.

37. Fujita Intensity Scale
In 1971, T. Theodore Fujita created a scale (often called the F scale) for
measuring intensity. Like the Mercalli Scale for earthquakes, the Fujita Scale
measures the degree of damage.

38. Mitigation: Early Warning
(Doppler Radar)
Doppler Radar
bounces radar waves
off of rain droplets,
measuring their
abundance, size, and
movement with the
objective of spotting
cloud rotation.
Doppler gives an
average warning time
of 13 min.

39. Mitigation: Early Warning
(Amateur Weather Watchers)
A program designed to teach amateur radio
operators how to identify and report severe
weather that might or might produce a
tornado to the National Weather Service

40. Mitigation: Early Warning
(Emergency Broadcast/Alert System)
• Begun in the 1950s to give warning of potential hazardous conditions,
including weather alerts.
• For tornadoes, a warning will be issued when:
– A tornado has touched the ground
– A funnel cloud is reported
– Radar picks up low level rotation
– A waterspout is heading toward land

41. Mitigation: Early Warning
(Sirens)

42. Mitigation: Early Warning
(Storm Chasers)
Storm chasers use special equipment to locate storms before they develop and study
them once they do.

43. Mitigation: Shelters

44. Mitigation: Research
(TOTO – old school)
Built by NOAA from 1979 to 1987.
Would fall after contact with tornado,
deploying sensors that would be pulled
into the tornado.

45. Mitigation: Research
(Storm Research Vehicles – new school)
The SRV Dominator is a modified 2011 GMC Yukon with armor, anchors, and a roll
cage for protection and a vertical radar and compressed-air launchers for parachuted
probes to study wind characteristics. It is designed to be directly in the path of a
tornado.

46. Mitigation: Building Codes
Hurricane ties.

48. Cold-weather Storms
As temperatures drop, rain can change to freezing rain, sleet, and snow,
creating a variety of hazardous weather conditions.

49. Freezing Rain
Freezing rain occurs when surface temperatures are below freezing, but the
atmosphere is above. Rain falls through the sky and turns to ice upon hitting
the ground.

52. Snow Storms & Blizzards
Snow is the result of a thick column of cold air immediately above the earth’s
surface. Blizzards occur if the snow is accompanied by high winds.

53. Snow Flakes
Snow flakes form as water vapor (not liquid) freezes upon contact with dust or
small ice crystals, growing into hexagonal structures large enough to fall to
the surface. Humidity and temperature determine the type of snow flake, such
as Utah’s “powder” and Missouri’s “mush.”