Weather Unit

1. WEATHER

3. Current
map

4. Pressure
! Recall the pressure
crushing the pop can
from the last unit
! The sum of the forces
from the moving air
molecules over an
area
! Average Sea level
pressure is 1010mb

5. What do these mean?
L- Low pressure, rising motion of
the air
H-High Pressure, sinking
motion of the air

6. So What’s Going on Here?
! What is wind?
! What would we expect the wind to look like in this
example?
H
L

7. WRONG!!!

8. ! Instead we see this…

10. Coriolis Effect
! Caused by the Earth’s Rotation
䡧Causes the Rotation of air around pressure
centers
䡧Opposite effects on southern hemisphere
䡧Simpsons video
! http://earth.nullschool.net/
! Example

11. • Air rises at a
Low
Pressure
Center
• Associated
with cloudy
and windy
weather
• North Pole
Loop
• Air sinks at
a High
Pressure
Center
• Associated
with nice
and calm
weather

12. Fronts
! Isotherm
䡧 Line of equal
temperature
! Isobar
䡧 Line of equal pressure
! Gradient is shown by
lines drawn close
together
䡧 Very important to
find fronts!

13. Fronts
! Leading Edge of different air mass
䡧 Temperature, humidity, wind direction
! 4 types
䡧 Cold Front
䡧Warm Front
䡧 Occluded Front
䡧 Stationary

15. Cold Front
! Brings in colder, drier air with a
sudden change in wind speed and
direction

16. Warm Front
! Brings warmer, more humid air with change in
wind direction

17. Occluded and Stationary Fronts
Occluded Front
• When cold front and warm front
run into each other
• Large amount of precipitation is
possible
Stationary Front
• Boundary between two air
masses
• Moves very slowly

18. Animation

19. Station Model

20. Reading Pressure

21. Weather at Fronts
! Cold Fronts
䡧 Clouds, rain/snow in narrow band right on frontal
boundary
䡧 Clear skies quickly follow frontal passage with strong N/
NW winds
! Warm front
䡧 Thin clouds/blanket of clouds with light rain possible
ahead of the frontal boundary
䡧 Winds shift to the south
! NW (top left) corner of Low Pressure Center
䡧 Heavy rain/snow fall possible
䡧 Caused by upper air configuration similar to occluded front

23. Current Weather
! http://www.hpc.ncep.noaa.gov/
! http://weather.cod.edu/satrad/
! http://www.aviationweather.gov/
! http://www.noaa.gov/

24. Jet Stream
! Pressure Centers control where fronts go
! Prevailing winds and the jet stream control
where pressure systems go
! Link

25. Clouds

26. What are clouds made of?
! Clouds are
made of
very small
droplets of
water or ice
crystals.

27. How do clouds form?
! Rising air cools as it rises, this causes water
vapor that is in the air to condense into a liquid
! What causes
Air to rise?

28. Types of Clouds
! Cumulus
䡧 “Puffy” with flat base
䡧 Can grow very tall
䡧 Time lapse of growth
Another Time Lapse Video

29. ! Stratus Clouds
䡧 Uniform layer
䡧 Usually dark gray
䡧 Can form at different altitudes
▫ Example: altostratus=middle altitude
! Cirrostratus=high altitude

30. ! Cirrus Clouds
䡧 Thin wispy clouds
䡧 Very high altitude (7-18km)
▫ Made of ice crystals

31. Special Cases
! Precipitation
䡧 When the cloud drops get too large to stay suspended
䡧 Gives the cloud a new name
䡧 Can be liquid or ice
! Cumulonimbus
䡧 nimbus cloud that is producing precipitation
! Nimbostratus
䡧 Stratus clouds that produce precipitation

33. Life of a Rain Drop

34. Link
Fronts can act as
LIFTING
MECHANISMS to
create clouds

36. Severe Weather
! When normal weather occurrences (wind, rain)
become more powerful than normal.
䡧 How do these form in non severe cases?
䡧 How can we make them severe?