1. Atmospheric Pressure, Air Masses, Fronts and Cloud Formation
Cold Fronts
Warm Fronts &
Weather Maps

2. Q1: Which canister is under higher pressure?
PV = nRT
P = Pressure
V = Volume
n = number (moles) of molecules
R = Gas Constant (doesn’t change at all)
T = Temperature

3. Q1: How does the number of molecules (n) relate to pressure (P)?
P1V1
P2V2 =
= R
n1T1
n2T2
Containers are the same size = Cross out Vs
Problem states equal temp = Cross out Ts
R is a constant (never changes) = Cross out R

4. Q1: How does the number of molecules (n) relate to pressure (P)?
P1V1
P2V2 =
= R
n1T1
n2T2
Containers are the same size = Cross out Vs
Problem states equal temp = Cross out Ts
R is a constant (never changes) = Cross out R

5. Q1: How does the number of molecules (n) relate to pressure (P)?= n1 n2
There are twice as many molecules (n1) in container A as there are in container B (n2).
This means that the pressure in container A (P1) is _________ as high as the pressure in container B (P2).
twice

6. Q2: Which pressure reading indicates a day of high atmospheric pressure=
29.92 in Hg =
1 atm =
760 mmHg
1013.2mb
29.92 in Hg b) 750 mm Hg
c) in Hg d) mb

7. Q 10-11:Map View of a Cold Front and a Warm Front
Warm Front – very gentle slope
Slow-moving steady rain
Cold Front – very steep slope
Fast-moving, Sudden storms

8. Cold Front
A cold front forms as a cold continental polar (cP) air mass pushes down between a cool Pacific maritime polar air mass (mP) and a warm, wet Gulf maritime tropical air mass (mT).

9. Warm Front
A warm front forms as the warm, wet Gulf maritime tropical air mass (mT) pushes north over the cool maritime polar (mP) air mass moving in from the Atlantic

10. Cold Fronts and Warm Fronts circle counter - clockwise around a Low Pressure Center

11. Q10-11: Cross Section of a Cold Front and a Warm Front
Where the cold, dense air of the HI meets the warm, lighter air of the LO, a front (boundary line) forms between the two air masses.

12. Q10-11: Cross Section of a Cold Front and a Warm Front
Cold Front – very steep
Fast-moving
Warm Front – very gentle
Slow-moving

13. Cross Section of a Cold Front (Question 10 - left side)
When the cold air mass is moving, it pushes in under the lighter, warmer air and forces the warm air upward. This creates a steeply sloping cold front.

14. Air Movement along a Cold Front
Cold Front – very steep slope
Fast-moving, Sudden storms

15. Air Movement along a Cold Front
Notice how much more suddenly the cold front will pass through. Sudden, violent storms followed by cool, clear dry weather are typical of Cold Front passages.

16. Cold Front

17. Cold Front
An animation:

18. Q 10 -11: Cloud Formation along a Cold Front and a Warm Front
Cold Front – Rapidly forming Cumulonimbus

19. Cloud Formation along a Cold Front
Stratocumulus clouds often lead the way a day ahead of a cold front.

20. Cloud Formation along a Cold Front
Altocumulus clouds often arrive just hours ahead of a cold front.

21. Cloud Formation along a Cold Front
Altostratus clouds also arrive just hours ahead of a cold front.

22. Cloud Formation along a Cold Front
However, Cold front thunderstorms are usually identified by rapidly forming, towering cumulonimbus clouds

23. Cloud Formation along a Cold Front
Cold front storms can usually be identified by rapidly forming, towering cumulonimbus clouds

24. Cloud Formation along a Cold Front
Cold front storms can usually be identified by rapidly forming, towering cumulonimbus clouds

25. Cumulonimbus Clouds

26. Cross Section of a Cold Front and a Warm Front
Cold Front – very steep
Fast-moving
Warm Front – very gentle
Slow-moving

27. Cross Section of a Warm Front
If a warm air mass is moving against a cold air mass, it will slowly rise above the cold air mass and squeeze it out of the way, forming a more gently sloping warm front (See next slide.)

28. Warm Front

29. Air Movement along a Warm Front
Warm Front – very gentle slope
Slow-moving steady rain

30. Air Movement along a Warm Front
A Warm Front typically brings a long, steady rainy spell (or snowstorm) that may last for several days.

31. Cloud Formation along a Warm Front (Q10-right side)
Cold Front – Rapidly forming Cumulonimbus
1) Cirrus
2) Cirrostratus
3) Altostratus
4) Nimbo-
stratus

32. Q 13: Which Weighs More- Wet Air or Dry Air? Molar Mass of Wet Air:
75% N2
20 % O2
0.96 % Ar
4 % H2O
Mair = .75 X 28 g/mol
+ .20 X 32 g/mol
X 40 g/mol
+ .04 X 18 g/mol
= g/mol
Molar Mass of Dry Air:
78% N2
21 % O2
1 % Ar
Mair = .78 X 28 g/mol
+ .21 X 32 g/mol
+ .01 X 40 g/mol
= g/mol
Heavier

33. Cloud Formation along a Warm Front
High, wispy cirrus clouds are the first sign several days before the arrival of a warm front.

34. Cloud Formation along a Warm Front
These are gradually replaced by: Cirrostratus and Altostratus clouds a day or two before the front

35. Cloud Formation along a Warm Front
As the warm front gets closer, stratus clouds…
Stratus

36. Cloud Formation along a Warm Front
… and finally waterlogged nimbostratus clouds appear, and may stay around for several days.
Nimbostratus

38. 2 Basic Kinds of Air Masses
3a. Northern Air Masses (Cold and Heavy)
3b. Tropical Air Masses (Warmer, Lighter)

39. North American Air Masses (3a, 3b 4 – 24)
cA = Continental Arctic
(very cold & dry)
cP = Continental Polar
(cold & dry)
mP = Maritime Polar
(cool & wet)
cT = Continental Tropical
(hot & dry)
mT = Maritime Tropical
(warm & wet)

40. North American Weather Fronts
Arctic Cold Front
(very cold & dry)
Polar Cold Front
(cold & dry)
Maritime Cold Front
(cool & wet)
Dry Line
(hot & dry)
Maritime Warm Front
(warm & wet)
Maritime Front