cold fronts, warm fronts, occluded fronts, precipitation wind jet stream

1. Winds, Air
Masses and
Fronts
Kella Randolph
M. Ed.
https://www.jmmnews.com/wp-content/uploads/2015/11/dandelion-in-wind-thumbnail.jpg

2. Why do hot air
balloons float?
• As the molecules in the gases that make up air
expand, they become lighter. A balloon that has been
filled with heated or hot air has lighter air than the air
surrounding it.
• Hot air rises and cold air, which is more dense, sinks.
• In these same ways clouds and air masses rise and
sink.
https://c1.staticflickr.com/7/6026/5924142387_88ccd100d8.jpg
https://publicdomainpictures.net/pictures/20000/velka/hot-air-balloon.jpg

3. Air masses
• Large sections of air are called air masses. Air masses can range from a
few hundred miles to a few thousand miles wide.
• Within an air mass the temperature and moisture content are uniform
throughout.
https://upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Earth_Global_Circulation_-_en.svg/1226px-
Earth_Global_Circulation_-_en.svg.png
https://c1.staticflickr.com/9/8175/7922872432_87de0225d4.jpg

4. Characteristics
of different air
masses
• Air masses get their
characteristics from the
region below them. For
example, air masses above
the North Pole will be cold
and dry, while air masses
over the tropical Caribbean
Ocean will be warm and
moist.
This Photo by Unknown Author is licensed under CC BY-SAThis Photo by Unknown Author is licensed under CC BY-SA
This Photo by Unknown Author is licensed under CC BY-SAThis Photo by Unknown Author is licensed under CC BY-SA

5. The source region gives
the air mass its
characteristics.
• There are five main
types of air masses.
Each is given a two-
word name.
https://upload.wikimedia.org/wikipedia/commons/thumb/7/76/Airmassesorigin.png/250px-Airmassesorigin.png

6. Each air mass has a two part name
Location
• Maritime = over ocean
• Continental = over land
Temperature
• Arctic = coldest air because it is
near the poles
• Polar = air masses from other
cold areas
• Tropical = very warm air masses
closest to the equator

7. maritime-Tropical (mT)
maritime-Tropical
(mT) - forms over
water and is warm
and humid_ (high
moisture content)
Image:
https://upload.wikimedia.org/wikipedia/commons/thumb/7/7
6/Airmassesorigin.png/250px-Airmassesorigin.png
https://upload.wikimedia.org/wikipedia/commons/thumb/7/76/Airmassesorigin.png/250px-Airmassesorigin.png

8. continental-Tropical
(cT)
continental-Tropical
(cT) - forms over
desert regions and
the air is HOT and
DRY.
Image:
https://upload.wikimedia.org/wikipedia/commons/thumb/7/
76/Airmassesorigin.png/250px-Airmassesorigin.png

9. continental-Polar (cP)
continental-Polar (cP)
- forms over COLD,
dry land. The air is
usually DRY.
Image:
https://upload.wikimedia.org/wikipedia/commons/thumb/7/7
6/Airmassesorigin.png/250px-Airmassesorigin.png

10. continental-Arctic (cA)
• continental-Arctic (cA) - these are
the COLDEST and DRIEST. they form
over frozen land
Image:
https://upload.wikimedia.org/wikipedia/commons/thumb/7/7
6/Airmassesorigin.png/250px-Airmassesorigin.png

11. maritime-Polar (mP)
• maritime-Polar (mP)
- the air is very COLD
but HUMID, because
it forms over cold
water
Image:
https://upload.wikimedia.org/wikipedia/commons/thumb/7/7
6/Airmassesorigin.png/250px-Airmassesorigin.png
https://upload.wikimedia.org/wikipedia/commons/thumb/7/76/Airmassesorigin.png/250px-Airmassesorigin.png

12. What is a front?
• A FRONT is the boundary
between two air masses. The
air masses have different
temperatures and moisture
contents. These differences
can often cause active weather
events.
https://www.earthonlinemedia.com/ebooks/tpe_3e/weather_systems/front_symbols.jpg

13. STATIONARY FRONT
When either a warm front or cold front
STOPS moving, it is stationary.
There are likely noticeable differences in
temperature and winds on either side of the
stationary front.
When it begins moving again, it resumes its
cold/warm front status.
Cyclones moving along a stationary front
often produce a lot of PRECIPITATION.
http://www.free-online-private-pilot-ground-school.com/images/occluded-front.gif

14. COLD front
The area where a cold air mass is replacing a
warm air mass. The air moving in is COLDER
and drier than the air ahead of it.
In the US, these generally move from the
northwest to the southeast.
On a map, the cold front is designated with a
BLUE solid line with TRIANGLES that point
toward the warmer air and the direction the
front is moving.
http://www.physicalgeography.net/fundamentals/images/warmfront.GIF

15. WARM Front
• The zone where warm air is replacing cold air.
The air moving in is warmer and more HUMID.
• In the US, these usually move from the
southwest to the northeast.
• The symbol for a warm front is a RED line with
SEMI-CIRCLES pointing toward the colder air it is
replacing.
https://upload.wikimedia.org/wikipedia/commons/thumb/e/ed/Warm_front.svg/1200px-
Warm_front.svg.png
http://www.physicalgeography.net/fundamentals/images/warmfront.GIF

16. OCCLUDED Front
• A cyclone forms when a cold front OVERTAKES a warm front.
The warm air is occluded from the center of the cyclone.
• On a map, an occluded front is represented by a PURPLE line
with alternating triangles and semicircles.
http://ww2010.atmos.uiuc.edu/guides/mtr/fcst/sfc/gifs/ofrnt2.gi
f
https://upload.wikimedia.org/wikipedia/commons/thumb/d/d2/Front_occlus_trowal_en.png/330px-
Front_occlus_trowal_en.png

17. How does a cyclone
form?
• A developing cyclone typically has a preceding
warm front (the leading edge of a warm moist air
mass) and a faster moving cold front (the leading
edge of a colder drier air mass wrapping around
the storm). North of the warm front is a mass of
cooler air that was in place before the storm
even entered the region.
• Text and image:
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr
/af/frnts/ofdef.rxml

18. Rotation intensifies
• As the storm intensifies, the cold front rotates
around the storm and catches the warm front.
This forms an occluded front, which is the
boundary that separates the new cold air mass
(to the west) from the older cool air mass
already in place north of the warm front.
Symbolically, an occluded front is represented by
a solid line with alternating triangles and circles
pointing the direction the front is moving. On
colored weather maps, an occluded front is
drawn with a solid purple line

19. Rapid changes
• Changes in temperature, dew point
temperature, and wind direction can occur with
the passage of an occluded front. In the map
below, temperatures ahead (east of) the front
were reported in the low 40's while
temperatures behind (west of) the front were in
the 20's and 30's. The lower dew point
temperatures behind the front indicate the
presence of drier air.

20. A noticeable wind shift also occurred across
the occluded front. East of the front, winds
were reported from the east-southeast while
behind the front, winds were from the west-
southwest. Common characteristics
associated with occluded fronts have been
listed in the table below.
https://3.bp.blogspot.com/_YY198IF63ko/S-
rE7G0K_1I/AAAAAAAAAYc/WDCRzG2wAMg/s1600/wind.jpg

21. DRY LINE -
The separation of a dry air mass
from a moist air mass.
There is a big difference in the
HUMIDITY from one side to the
other.
Dry air behind the dry line lifts the
moist air ahead of it. This creates
THUNDERSTORMS.

22. HUMIDITY
• Water vapor is the gaseous version of water.
If we examine the amount of water vapor in
the air, it is referred to as the HUMIDITY. If the
air feels thick or moist, the humidity is high.
• High humidity can make the outdoors look
blurry. Also, perspiration does not dry from
our skin and we may feel damp and clammy on
very humid days.
https://c2.staticflickr.com/2/1286/768739926_55ce7b1350_z.jpg?zz=1

23. Weather
games
• https://scijinks.gov/
• https://scijinks.gov/resources/icons/jet
-stream.png
• https://ssec.si.edu/weather-lab
• Image
https://ssec.si.edu/sites/default/files/style
s/550-
/public/WeatherLab_1.png?itok=o7YJJcbY
• https://ssec.si.edu/disaster-detector
• Image:
https://ssec.si.edu/sites/default/files/style
s/550-
/public/DisasterDetector_TitleScreen.png?
itok=ag3vqJut