Download Weather Fronts Lesson - staff.harrisonburg.k12.va

Types of Fronts
Stationary front A front that is not moving.
Cold front is a leading edge of colder air that is replacing warmer air.
Warm front is a leading edge of warmer air that is replacing cooler air.
Occluded front: When a cold front catches up to a warm front.
Dry Line
Separates a moist air mass from a dry air mass.
A.
Cold Front is a transition zone from warm air to cold air.
A cold front is defined as the transition zone where a cold air mass is
replacing a warmer air mass.
Cold fronts generally move from northwest to southeast.
The air behind a cold front is noticeably colder and drier than the
air ahead of it.
When a cold front passes through, temperatures can drop more
than 15 degrees within the first hour.
The station east of the front reported a temperature of 55
degrees Fahrenheit while a short distance behind the front, the
temperature decreased to 38 degrees.
An abrupt temperature change over a short distance is a good
indicator that a front is located somewhere in between.
B.
Warm Front. A transition zone from cold air to warm air.
A warm front is defined as the transition zone where a warm air
mass is
replacing a cold air mass.
Warm fronts generally move from southwest to northeast and
the air behind a warm front is warmer and more moist than the air
ahead of it.
When a warm front passes through, the air becomes noticeably
warmer and more humid than it was before.
Diagram of Warm and Cold Fronts
Looking at a Cold Front in more detail
Another view of a Cold Front
Looking at details of a Warm Front
Another view of the Warm Front
C.
Stationary Front a front that is not moving.
When a warm or cold front stops moving, it becomes a stationary
front.
Once this boundary resumes its forward motion, it once again becomes
a warm
front or cold front.
A stationary front is represented by alternating blue and red lines
with blue
triangles pointing towards the warmer air and red
semicircles pointing towards the colder air.
D. Occluded Front - when a cold front overtakes a warm
front.
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.
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
front is moving.
and circles pointing the direction the
Formation of an Occluded Front
Two
Types of
Occluded
Fronts
Special situation of an Occluded Front
Dry Line is a moisture
boundary.
A dry line is a boundary
that separates a moist air
mass from a dry air
mass.
Also called a "Dew Point Front", sharp changes in dew
point temperature can be observed across a dry line.
Dry lines are most commonly found just east of the
Rocky Mountains, separating a warm moist air mass to
the east from a hot dry air mass to the west.
Actual Weather
Map
Yellow dashes
mark the Dry Line
On the previous weather map ;
Dew points east (ahead) of the dry line shown above range from
the upper 50's to low 70's with winds from the southeast.
West of the dry line, dew points were in the 20's and 30's, a
decrease of nearly 50 degrees.
Air temperatures ahead of the dry line were generally in the 70's
and 80's while behind the dry line, temperatures ranged from the
mid 80's to mid 90's.
Drier air behind dry lines lifts the moist air ahead of it, triggering
the development of thunderstorms along and ahead of the dry line
(similar to cold fronts).
It is not uncommon for tornadic super cells to develop along a dry
line.