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Counting Cold Fronts
Mexican meteorologists count the cold fronts that extend south of the U.S. border into Mexico. This week's cold front was the 5th to reach Mexico this fall, so meteorologists called it "Cold Front #5."

Why count cold fronts?
Just as hurricanes are named because they are significant weather events, the cold fronts that reach Mexico can bring strong storms and freezing temperatures to that country during the winter. Cold fronts do not reach Mexico during the summer months, but weather patterns shift in the fall. The northern hemisphere is titled away from the sun. Large, cold air masses can form in the north. The cold air reaches farther and farther south as fall becomes winter. In the spring, the last cold front to extend south into Mexico typically occurs in May.

How are cold fronts related to monarchs and migration?
In the fall, cold fronts (and the air masses that follow) typically provide the north winds monarchs use to migrate to Mexico. In the winter, cold fronts can reach as far south as the monarch overwintering sites in central Mexico. The fronts can cause severe storms, and the cold air masses can cause sub-freezing temperatures in the monarch's winter colonies.

How to Count Cold Fronts
You can count Mexico's cold fronts this season. Last year, meteorologist counted a total of 48 and the last one occurred on May 14, 2012. What will this winter bring?


Cold Front Number 5

In Spanish, a cold front is called a "frente frio" and is abbreviated "FF."