Have you ever spent an afternoon in the backyard, maybe grilling or enjoying a game of croquet, when suddenly you notice that everything goes quiet? The air seems still and calm -- even the birds stop singing and quickly return to their nests.
After a few minutes, you feel a change in the air, and suddenly a line of clouds ominously appears on the horizon -- clouds with a look that tells you they aren't fooling around. You quickly dash in the house and narrowly miss the first fat raindrops that fall right before the downpour. At this moment, you might stop and ask yourself, "Why was it so calm and peaceful right before the storm hit?"
It's an intriguing phenomenon that people have recognized for centuries, but what on Earth causes this calm? And why do whip-like winds, dropping temperatures and rumbling thunder sometimes precede storms instead of a peculiar and eerie calm?
Do you want a hint at what might be at the root of this old sailors' adage? Think of all the different types of storms you've seen -- one variety of storm can have a different effect on the atmosphere than another. There are brief thunderstorms that rattle through like a couple of rowdy frames at the bowling alley, and there are long, tumultuous downpours that drown the streets. And then there are the strongest of all, like massive, violent hurricanes or spinning, furious tornadoes. All these different manifestations of intense weather happen because the interactions in the atmosphere can unfold in a variety of different ways, to vastly different effects.
So, if the weather is calm and fair for your backyard barbeque, does that mean you should make backup plans indoors? Read on to the next page for the answer.
The Calm Before the Storm
So is there a calm before the storm? You may have already guessed the answer. Sometimes there is; sometimes there isn't. Under the right conditions, an eerie or peaceful calm will befall your picnic before a storm moves in. Other storms skip the calm and proudly announce their presence by instantly unleashing bad weather. Let's take a look at what goes on inside a storm to understand more about how this works.
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Storms need warm, moist air as fuel, and they typically draw that air in from the surrounding environment. Storms can draw in that air from all directions -- even from the direction in which the storm is traveling.
As the warm, moist air is pulled into a storm system, it leaves a low-pressure vacuum in its wake. The air travels up through the storm cloud and helps to fuel it. The updrafts in the storm, however, quickly carry the air upward, and when it reaches the top of the cloud mass, this warm moist air gets spit out at the top. This air is sent rolling out over the big, anvil-shaped head of the thunderclouds or the roiling arms of hurricanes. From there, the air descends -- drawn back toward lower altitudes by the very vacuum its departure created in the first place.
What's important for our purposes is that descending air becomes warmer and drier (a good thing after its trip through the cloud, which involved cooling and condensation). Warm, dry air is relatively stable, and once it blankets a region, it stabilizes that air in turn. This causes the calm before a storm.
On the other hand, different situations can produce weather that's quite a bit uglier and not at all calm before a storm hits. For example, think of large storm systems. They're more complex than a single, unified storm, and their interactions usually don't produce any type of calmness.
Though we understand weather better than in years past, predicting it with perfect accuracy (calm or not) still remains somewhat of a mystery. For more information about storms and weather, visit the links on the next page.
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More Great Links
- Dorst, Neal. "What's it like to go through a hurricane on the ground? What are the early warning signs of an approaching tropical cyclone?" Atlantic Oceanographic and Meteorological Laboratory Hurricane Research Division. 8/13/2004. (5/1/2008) http://www.aoml.noaa.gov/hrd/tcfaq/H5.html
- Encyclopedia Britannica. "Tropical Cyclone." (4/30/2008) http://www.britannica.com/EBchecked/topic/606551/ tropical-cyclone/247932/Naming-systems#ref=ref848914
- Foster, James and Adler, Robert. "Is there really a period of calm before a storm?" Goddard Space Flight Center. 9/26/2003. (4/27/2008) http://www.gsfc.nasa.gov/scienceques2003/20030926.htm
- The Weather Network. "Calm Before the Storm." (5/1/2008) http://www.theweathernetwork.com/index.php?product= glossary&pagecontent=glossaryindex&pagecontent=calmbeforethestorm
- Tarbuck, Edward and Lutgens, Frederick. "Earth Science Eleventh Edition." Pearson Prentice Hall. 2006. (5/1/2008)
- Tomov, Beverly. "Why is there a calm before a storm?" Earth and Sky Radio Series. (5/1/2008) http://www.earthsky.org/radioshows/48974/why-is-there-a- calm-before-a-storm