1. Fronts How to identify fronts on a weather map?
Frontal zone – strong T gradient

2. Thickness
A measurement of how warm (high value) or cold (low values) a layer of the atmosphere is.
Thickness gradient can be used to find fronts (strong gradient region).
-- Hypsometric equation

3. Thickness

4. Cold Fronts
Cold Front (
A transition zone where a cold air mass is replacing a warm air mass
Air is pushed up rapidly. Front quickly passes. Stormy!
Moving speed of a front at the developing stage is ~ 25 knots (12.5 m/s) and the speed is reduced as the front "matures“.
The slope of the front (the ratio of the vertical to the horizontal scale) is about 1/50 to 1/100

5. Cold Fronts
Cold Front
A transition zone where a cold air mass is replacing a warm air mass
warm
cold
Or blue line
Front symbol is located at the warm air edge of the temperature gradient.
Large temperature contrast across it (10 oC across 100 km)

6. Cold Fronts Ci: Cirrus Cs: Cirrostratus
Cb: Cumulonimbus Cu: Cumulus mediocris Cu Ci Cs Cb

7. Warm Fronts
Warm Front (
A transition zone where a warm air mass is replacing a cold air mass
Or red line
Air is pushed slowly. Rainfall is generally more gentle and extended in duration.
The slope of the front (the ratio of the vertical to the horizontal scale) is about 1/200
Moving speed is about 8 m/s (slower than cold fronts).

8. Warm Fronts Ci: Cirrus Cs: Cirrostratus
As: Altostratus Ns: Nimbostratus
Sc: Stratocumulus St: Stratus St Ns Sc As

9. Cyclone, Cold Front, and Warm Front
direction of
propagation L
warm air mass
cold air mass
warm front
cold front
996
992
988 ** 32 31 .. 39 37 49 46 . 56 52

10. Fronts
Cold front
Warm front

11. Occluded and Stationary Fronts
Occluded Front
when a cold front overtakes a warm front.
(Cold fronts moves faster than warm fronts)
Or purple line
Or red-blue line
Stationary Front
A front that moves very slow
warm
cold

12. Occluded Front Formation of a warm front type occlusion
Formation of a cold front occlusion
From

13. Occluded, Warm, and Cold Fronts

14. Frontogenesis Isobars Thickness
Winds deflect to the right in the Northern hemisphere due to the Coriolis force

15. Frontogenesis to (Extratropical) Cyclone FormationW
Front W C C
Draw the front at the warm side of the front
Cyclone L W

16. Initial Cyclone Formation
Isobars
Thickness
The strong thickness gradient zone (TGZ) passing the center of the cyclone.
Draw at the warm side
Draw at the warm side

17. The strong TGZ is away from the center of the cyclone (occluded front)
Mature Cyclone
Isobars
Thickness
The strong TGZ is away from the center of the cyclone (occluded front)

18. Decaying Cyclone
Isobars
Thickness

19. Cold Front 1 2 3 4

20. Fronts

21. Fronts

22. What stage of the cyclone’s life cycle?
Mature Cyclone
(animation)

23. Initial cyclone formation
Where are fronts? What’s the Stage of the Cyclone?
Initial cyclone formation

24. Dry line
A boundary separates a moist air mass from a dry air mass (sharp dew point gradient). Occurs in the spring and early summer seasons around Texas, New Mexico, Oklahoma, Kansas, and Nebraska. If there is enough moisture and instability in the warm air, severe storms can occur.
Subsidence warming –
dry and hot
Warm, moist air
Td : 50’s to 70’s
T: 70’s to 80’s
Hot, dry air
Td : 20’s to 30’s
T: 80’s to 90’s
Dry line
Rocky Mountains

25. Dry line
Dew points

26. Dry line Some people like to chase dryline storms!
It propagates eastward in the morning, then stalls by mid-afternoon, and retreats back to high plans by early evening as the hot dry side is destroyed by radiative cooling.

27. Thunderstorms
Occurs when atmosphere has a lot of energy (how do you know?).
Rain, hail, thunder, lightning, flash flood, and gust wind
Unstable atmosphere – using indices to help check.
Mature stage
dry
air
Dissipation stage
Cumulus stage
(Developing stage)