Polar Vortex. Bombogenesis. Thundersnow.
Many of these words have made headlines recently, most notably because they sound new, or at least unfamiliar.
But it turns out that forecasters have used these words for decades, if not centuries.
News outlets and social media lit up around the start of the year with words "polar" and "vortex". Atmospherically, an arctic air mass passed through the eastern half of the United States,
dropping temperatures as low as 30 degrees below zero.
While January 2014 may seem to be the polar vortex's debut, Stu Ostro, senior meteorologist with The Weather Channel, notes that
the phrase has been used within scientific research papers as early as 1939.
What Is It?
One of several semi-permanent weather systems over the Earth, the polar vortex is an area of low pressure in the upper atmosphere, primarily in the stratosphere, which is the layer of the atmosphere above which most of our sensible weather occurs. This vortex is often in place near the poles, and it is nothing new.
(
MORE: Polar Vortex Facts and Myths)
The Northern Hemisphere polar vortex frequently, but not always, centers in two main areas: near
Canada's Baffin Island and over
northeast Siberia. (There is a southern hemispheric version of the polar vortex within which the depletion of the upper-atmospheric ozone layer occurs.)
The vortex is strongest in winter, thanks to an increased temperature contrast between the polar regions and the mid-latitudes, including the United States.
Occasionally, pieces of the larger spin can break off and sweep toward southern Canada, helping to drive arctic cold plunges into the U.S.
Next is a meteorological term that describes a rapidly intensifying storm system.
Bombogenesis
In February, a new weather term entered the American public's lexicon:
bombogenesis.
The word sounds ominous, but in reality, the process happens fairly frequently.
What is it?
When a low pressure system drops at least 24 millibars within 24 hours, meteorologists say that the low is undergoing bombogenesis, or is "bombing-out". The term is used to describe the low's explosively rapid development.
So what happens when a meteorological "bomb" strengthens?
Wind speeds increase and precipitation can become more intense, sometimes creating heavy snowfall and potential blizzard conditions when enough cold air is available. This happened in February, when
Winter Storm Quintus dropped 31 millibars within a span of 24 hours. Heavy snow rates can also occur during bombogenesis, which is sometimes accompanied by lightning.
Next is a severe weather term that is coined as a straight-wind "analog" to the word tornado.
Derecho
This word inevitably pops up every summer when large clusters of storms ride the periphery of a ridge, or an upper-level high pressure system.
What is it?
Derechoes are large clusters of thunderstorms that produce widespread wind damage, usually as a result of one or more curved lines of thunderstorms known as
bow echoes. These thunderstorm clusters leave long and wide swaths of straight-line wind damage, and they can pack winds that can be as strong as 50 to 100 mph or higher.
According to the Severe Prediction Center, a line or cluster of thunderstorms can only be classified as a derecho "if the swath of wind damage extends for more than 240 miles, includes wind gusts of at least 58 mph along most of its length, and it contains several, well-separated 75 mph or greater wind gusts."
The word derecho comes from the Spanish language, and it means straight ahead. This suggests that these storms are characterized by their powerful straight-line winds. Contrast this to the word
tornado, which is
derived from the Spanish word "tornar" and means to turn.
Because of the widespread nature of the winds in a derecho, the impact is somewhat like that of a landfalling hurricane and affects a much greater area than most tornadoes. The extensive swath of
downed trees and power lines causes a
major cleanup and restoration effort, and often requires relief workers to come in from other states to aid in these efforts.
http://www.wunderground.com/news/polar-vortex-derecho-bombogenesis-new-weather-terms-20140410
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