1. Cold Fronts

2. Cold Fronts
• When cold, continental polar air advances into
a region that is occupied by warmer air, this
condition results in a cold front.
• As it happens with warm fronts, the area of
the cold front (and warm front) nearest the
ground moves more slowly due to friction as
compared to the air that is aloft.
• Thus, the cold front steepens as it moves.

3. Cold Fronts
• On average, cold fronts are about twice as
steep as warm fronts.
• In addition, cold fronts advance at speeds of
20 to 35 miles per hour compared to 15 to 20
miles per hour with warm fronts.
• These two differences, steepness and rate of
movement account for the more violent
nature of cold fronts.

4. Cold Fronts
• The arrival of cold fronts is sometimes
preceded by alto-cumulus clouds.
• As the front advances, mainly from the west
and northwest, towering clouds can often be
seen in the distance.
• Close to the front, a band of dark, ominous
clouds foretells the ensuing weather.

5. Cold Fronts
• The forceful lifting of warm, moist air along
the cold front is often so rapid that the
released latent heat increases the air’s
buoyancy.
• Heavy downpours and vigorous wind gusts
that are associated with mature
cumulonimbus clouds frequently result.

6. Cold Fronts
• Because a cold front produces roughly the
same amount of lifting as a warm front but
over a shorter distance, the precipitation
intensity is greater, but of shorter duration.
• Marked temperature drop and windshift from
the southwest to the northwest usually
accompanies the front’s passing.

7. Cold Fronts
• The sharp temperature contrast and
sometimes violent weather along cold fronts
are symbolized on a weather map by a blue
line with blue triangular points extending into
the warm air mass.

8. Cold Fronts

9. Cold Fronts
• Most often, the weather behind a cold front is
dominated by subsiding air within a
continental polar air mass.
• Thus, the drop in temperature is accompanied
by clearing that begins soon after the front
passes.
• Although the effect is a fair amount of cooling
of air aloft, the effect near ground level is
relatively minor.

10. Cold Fronts
• In winter, the long, cloudless nights that follow
the passage of a cold front result in radiation
cooling that reduces surfaces temperatures.
• When a cold front moves over a relatively
warm surface, radiation emitted from the
Earth can heat the lower atmosphere enough
to produce shallow convection.
• This can result in low cumulus or
stratocumulus clouds behind the front.