Cold fronts occur when cold polar air advances into warmer air. They are steeper and move faster than warm fronts, resulting in more violent weather. As the cold front passes, temperatures sharply drop while heavy rain and strong winds can occur along the front due to rapid lifting of warm air. Clearing usually follows the front as polar air moves in.

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.