Weather Whys

By Texas A&M University —

Q: What causes cold fronts?

A: The simple explanation is that a cold front is where a cold air
mass is replacing a warm air mass, says Brent McRoberts of Texas A&M
University. “The air mass behind it is noticeably colder and it pushes
out the warmer air,” McRoberts explains.

“As a cold front moves into an area, the heavier, colder air moves
out the warmer, lighter air its replacing. If the warm air is humid
enough, water vapor in it will condense and rain can occur, which is why
cold fronts often trigger thunderstorms. The rotation of the earth
helps to form the wind that flows between air masses.”

Q: How fast can the temperature drop when a cold front arrives?

A: Amazingly fast, McRoberts adds. It is not uncommon for the
temperature to drop 15 degrees or more in just one hour after a cold
front arrives. “There are some incredible stories about temperature
changes,” he adds. “On Dec. 20, 1836 in Illinois, the temperature went
from 40 degrees to 0 in just a few hours. And on Jan. 22, 1943 in South
Dakota, the town of Spearfish was at the edge of an arctic air mass but
still under a temperature inversion area. At 7:30 a.m., the temperature
in Spearfish was -4 degrees and within two minutes, went to 45 degrees
above 0 because of warm winds associated with the inversion. By 9 a.m.
the temperature was up to 54 degrees, but the conditions changed and the
temperature fell to -4 degrees. A 58-degree temperature drop had
occurred in only 27 minutes, still believed to be a record.”

The National Weather Service estimates there are about 100,000
thunderstorms a year in the U.S., but only about 10 percent of those are
classified as severe. But the severe storms can cause amazing damage
and even loss of life.”

The rest are used by the Federal Aviation Administration (FAA) or by the Department of Defense.”


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