Below are some guidelines on what you should know

from this unit on fronts and air masses

Objective 1: Recognize the characteristics of the different air masses that affect our weather in the U.S.:

Large blobs of air with a relatively uniform temperature and moisture content are termed air

masses. They generally take on the characteristics of their place of origin (for example, an air

mass originating in Canada would typically be cold and dry, since it formed at a high latitude

over land).

Objective 2: Identify the boundaries between the air masses as fronts, and determine the type of front:

If the cold air mass is displacing the warmer one, the boundary is labelled a cold front on the surface map. If the warm air mass is moving northward and displacing a cooler air mass, the boundary is labelled a warm front.

Objective 3: Be able to determine the type of air mass in place using surface data:

Look closely at the surface plot above:

-southeastern portion of the map has southerly winds, high temp's and high dewpoints (mT air)

-northwestern portion of the map has NW winds, lower temp's and low dewpoints (cP air)

Objective 4: Analyze a surface map to determine the location and type of front:

We can find the location of a front using the following surface map observations:

-wind direction: look for a shift in wind directions (on the map above, notice the southerly

winds on the eastern half of the map, while the western portion has predominantly NW

winds...the front probably lies somewhere on the map where the wind shift takes place.

-temperatures: look for a change in temperature from one part of the map to another. In the

example above, notice that the temperatures in VA, WV, & NC are in the 50's, while just a

bit further to the west in central KY and TN the temperatures are in the 30's. Such a big

swing in temperatures is a great clue as to the location of the front.

-dewpoints: Just like temperatures, a radical change in dewpoints on a surface map can also

help you pinpoint the location of a front: look at the dewpoints in western NC and eastern

TN: in the upper 40's. Now, look at the dewpoints in central TN and KY: in the 30's. That's

a good indicator the front lies somewhere between the two locations!

-cloud coverage/precipitation: while not as reliable as the previous three, many times you

will indeed find higher % cloud cover and precipitation in the neighborhood of a front. Keep

in mind though, that clouds and precipitation can occur well in advance of a front (this is

especially true of warm fronts), so use this factor in conjunction with the other three when trying

to discern the location of a front!

Here are some other images to help you learn how to locate a front:

Note the wind shift from SW to NW...so position "A" is the most likely place for the front.

Notice the drop in temperatures and dewpoints behind front position "A". Sometimes temperatures don't drop much, but lower dewpoints still signal the arrival of drier air behind a cold front.

Note the cloud cover along and ahead of the front. Many times you will see this, including precipitation accompanying the clouds, but again, keep in mind that precipitation and clouds can form well ahead of an advancing front.

So far, we have concentrated on cold fronts, so here is an overview

on locating warm fronts:

Note again the following factors:

-wind direction: a shift from E before to S after passage

-temperature: an increase after passage

-dewpoint: an increase with warm, moist air

-cloud cover/precipitation: heaviest cloud cover ahead of front

Position "B" is the most likely location for the front !

Objective 5: Recognize the typical wind directions associated with fronts on surface maps:

Objective 6: Evaluate weather conditions on a surface map and identify the type of frontal boundary creating those conditions:

Five tornado watches along an intense line of thunderstorms stretching

from the Great Lakes to the Gulf Coast should give you a clue that a

cold front is moving eastward! Learn to recognize the typical weather

found along each type of front using station models and radar imagery!