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Farmers Almanac
The 2014 Farmers Almanac
Farmers' Almanac

Extreme Weather Stories

Extreme Weather Stories

THE GREATEST STORM ON EARTH HURRICANES:

Hurricanes are tropical cyclones and can be as great as 500 miles across. They have been called the greatest storms on Earth, and, indeed, a fully developed hurricane can extend upwards from the surface of the sea to the base of the stratosphere (18 miles). Each hurricane usually contains a calm eye at its center, perhaps 10 or more miles wide; yet circulating immediately outside that eye are fierce winds of at least 75 to perhaps 155 miles per hour. The central core of a storm possesses a higher temperature than the surrounding atmosphere. Hurricanes are usually accompanied by torrential rainfall, which can exceed 20 inches, and severe turbulence. In addition, before making landfall, a hurricane can generate storm surges. The low pressure in the eye of the storm literally sucks the ocean surface upward, creating a bulge several feet high. As a storm approaches land, a bulge can become 15 feet or higher due to the added effect of the wind pushing the water ahead of a storm on the right side of its track.

A hurricane is essentially a “heat engine” born in the heat of the tropics. It can last for many days as it moves over warm, flat stretches of ocean water, and requires a specific combination of warmth, moisture, and atmospheric instability to develop. Ocean water must have a temperature of at least 80oF to initiate storm development. Interestingly, the exact mechanism of tropical cyclone formation is still not fully understood, even though it has been under intensive study for many years.

Most hurricanes are born out of “easterly waves,” when an upper atmospheric disturbance travels westward from West Africa or the adjacent waters across the North Atlantic Ocean. As a disturbance moves westward, the warm, moist tropical air along its path rises, leading to the formation of clouds and clusters of thunderstorms. A deflective effect, known as the Coriolis force, diverts the surrounding airflow into a somewhat circular pattern. As water vapor condenses into water droplets, it y waves are observed during a typical summer, only about 10 percent of these actually lead to storm formation. If an easterly wave manages to develop circulation, it is categorized as a tropical depression. If the winds within the circulation reach or exceed 39 miles per hour, it becomes a tropical storm. If the winds exceed 74 miles per hour, it becomes a hurricane. The tropical storm season runs from June 1 through November 30. In a typical season, there is an average of ten tropical storms, of which five will be hurricane strength. In 1933, there were 21 tropical storms, nine of which became hurricanes. The traditional peak of the hurricane season is September 10; at least one hurricane is usually lurking somewhere in the Atlantic basin on this date. June and July are considered slack months, but by the second week of August, tropical activity noticeably increases. After September 10, activity declines, but only slowly at first. Only after the second week of October does tropical storm activity drop precipitously. An old Florida proverb seems to sum it up best:

May … Not today
June … Radios in tune
July … All stand by
August … Beware you must
September … Time to unlimber
October … Not yet over
November … Remember

IT’S A TWISTER! IT’S A TWISTER! TORNADOES!:

No doubt you’ve seen the 1939 movie classic The Wizard of Oz and remember the famous scene in which a tornado bore down on Dorothy Gale’s Kansas home, physically lifting it off its foundation. But have you ever wondered what causes such a powerful weather disturbance to form? A tornado is a concentrated twister, the most vicious wind machine of all. Tornadoes are generated by severe thunderstorms. As cool, dry air pushes into a warm and humid region, showers and thunderstorms form and gather ahead of the advancing cool air mass. In the process, strong updrafts occur in the damp air inside of a thunderhead, strengthening and setting off extreme turbulence. This ultimately sets off a cyclonic machine inside of the cloud. The result: a tornado, which at first appears to extend down from the base of the cloud, much like a giant twisting funnel. Wherever a tornado touches the ground, tremendous damage can occur, thanks to a combination of powerful winds and extremely low pressure.

A typical tornado is usually less than a thousand feet in diameter, moves with an average forward speed of 30 miles per hour, and rarely lasts more than a minute or two in any one specific place. But that’s all the time a tornado needs- with winds that can exceed 260 miles per hour in the most extreme cases, destruction is almost instantaneous. Unlike what was portrayed in The Wizard of Oz, were a tornado to pass over, the house likely would not be lifted off the ground-but be totally destroyed. There is a special 0 to 5 scale to classify the strength of tornadoes, called the Fujita-Pearson (or F) scale, created by T. Theodore Fujita and Allen Pearson. An F0 tornado is the weakest type, with winds of 40 to 72 mph, and capable of light damage. In contrast, an F5 tornado can produce violent winds in excess of 261 mph. The damage associated with an F5 tornado is classified simply as “incredible.” By far, the worst tornado in U.S. history was the Tri-State Tornado of March 18, 1925. This tornado traveled for over 200 miles through Missouri, Illinois, and Indiana-one of the longest known paths for any tornado. It killed 695 people and carved a path of destruction measuring as much as a mile wide in some locations.

The part of the United States that sees the greatest frequency of tornado activity is a band about 100 to 200 miles wide that runs from North Central Texas to the Dakotas. This is sometimes referred to as tornado alley. In contrast, the western third of the United States rarely sees any tornado activity at all, but even there, there are exceptions, like the tornado that passed through Salt Lake City, Utah, in August 1999. Tornadoes tend to be more common in late spring, and occurrences drop off considerably by July. This is because the low-pressure areas that spawn severe thunderstorms can be quite intense in April and May, but usually weaken considerably and drift off toward Canada during the summertime.

WHAT THE HAIL? THUNDERSTORMS:

Perhaps you’ve noticed that the first drops of a thunderstorm are always the biggest. The reason is simply that only the heaviest drops can fall through the powerful updraft winds inside of a thunderstorm. Those early pilots who foolishly attempted to fly straight through towering thunderhead clouds quickly found out about the updrafts the hard way. Heavy airliners were turned upside down, and wings were ripped off Air Force bombers. Pilots claimed that winds in excess of hurricane force (74 miles per hour) existed inside thunderheads. Those winds could blow rapidly upwards (an updraft) or downwards (a downdraft).

Today, commercial airline pilots simply fly around such storms. Many raindrops inside a developing thunderstorm are carried aloft by updrafts. While the lower part of a thunderhead cloud contains warm air, at altitudes above 25 thousand feet, air temperatures are always below freezing (32oF). Water droplets at such high altitudes freeze, a process called riming or icing. In the early days of aviation, before heaters were installed on airplanes, this icing caused many crashes and almost claimed the life of Charles Lindbergh, the first man to fly across the Atlantic Ocean. Since most thunderheads can grow to 40 or even 50 thousand feet in height, it is possible for raindrops to be caught in an updraft, carried tens of thousands of feet aloft, and quickfrozen into hail. An ice particle may actually be tossed up and down several times through a thunderhead, melting partially and refreezing, before finally becoming heavy enough to fall through the violent updrafts to the ground. Once a drop has frozen, other drops can freeze on it, and so a hailstone grows-sometimes into a huge iceball. Hailstorms are most frequent in eastern Wyoming, eastern Colorado, and western Nebraska. In some parts of the country-Florida, for instance-you can frequently encounter severe thunderstorms, but will rarely see hail. The reason is that in such very warm climates, hail will fall through a warm, moist layer of air at the bottom of the thunderstorm and will almost always melt before it reaches the ground.

If you ever encounter a thunderstorm that drops hailstones, collect a few hailstones and examine them closely with a magnifying glass. With a sharp knife, try cutting one in half. What do you see? What you may find are layers-several distinct lines around the center drop. That means that the original large raindrop made several round trips up and down through the freezing zone before finally becoming heavy enough to resist the updraft and fall to the ground as hail. Often hail falls over areas of 100 feet to 2 miles wide and 5 to 10 miles (or more) long as a thunderstorm moves downwind. These areas, known as hailstreaks, can actually turn white from a heavy accumulation of hailstones. A severe storm on June 3, 1959, covered Selden, Kansas, with hailstones to a depth of 18 inches. The total destruction of crops, especially in the Great Plains where hailstorms are frequent, may result. Injury and even death may come to both animals and humans when caught in a heavy bombardment of large hail. Hailstones can range in size from that of a pea to that of a grapefruit. The largest hailstone ever measured fell at Coffeyville, Kansas on September 3, 1970. It had a circumference of 17.5 inches and weighed 1.671 pounds. Ouch!

Wind SpeedMPH Wind SpeedKnots Beaufort Number National Weather Service Description Effect of the Wind on Land Effect of the Wind on the Sea Wave Height
0-1 0-1 0 Calm Smoke rises vertically Sea appears mirror-like
Calm
1-3 1-3 1 Light Air Direction shown by smoke drift; vane still Ripples with an appearance of scales; no foam 0.25 ft
4-7 4-6 2 Light Breeze Leaves rustle; weathervane moves Small wavelets; crests of glassy appearance, not breakng 5-1 ft
8-12 7-10 3 Gentle Breeze Leaves in constant motion; wind will extend a light flag Large wavelets; crests begin to break; scattered whitecaps 2-3 ft
13-18 11-16 4 Moderate Breeze Raises dust; small branches move Small waves, becoming longer; numerous whitecaps 3-5 ft
19-24 17-21 5 Fresh Breeze Small trees with leaves begin to sway Moderate waves, taking longer forms; many whitecaps, some spray 6-8 ft
25-31 22-27 6 Strong Breeze Large branches in motion; difficult to control an umbrella Larger waves forming; whitecaps everywhere, more spray 9-13 ft
32-38 28-33 7 Moderate Gale Whole trees in motion; noticeable difficulty in walking Sea heaps up; white foam from breaking waves begins to be blown in streaks 13-19 ft
39-46 34-40 8 Fresh Gale Small branches may be broken; walking against the wind becomes very difficult Moderately high waves of greater length; edges of crests begin to break into spindrift; foam is blown in well-marked streaks
18-25 ft
47-54 41-47 9 Strong Gale Slight damage to structures; shingles blown off roofs High waves; sea begins to roll; dense streaks of foam; spray may begin to reduce visibility 23-32 ft
55-63 48-55 10 Gale Considerable damage to structures; trees uprooted Very high waves with overhanging crests; sea takes white appearance as foam is blown in very dense streaks; rolling is heavy and visibility is reduced 29-41 ft
64-74 56-64 11 Storm Widespread damage to structures; rarely occurs inland Exceptionally high waves; sea covered with white foam patches; visibility futher reduced 37-52 ft
75+ 65+ 12 Hurricane Extreme destruction Air filled with foam; sea completely white with driving spray; visibility greatly reduced 45+ ft

If you notice a hole in the upper left-hand corner of your Farmers' Almanac, don't return it to the store! That hole isn't a defect; it's a part of history. Starting with the first edition of the Farmers' Almanac in 1818, readers used to nail holes into the corners to hang it up in their homes, barns, and outhouses (to provide both reading material and toilet paper). In 1910, the Almanac's publishers began pre-drilling holes in the corners to make it even easier for readers to keep all of that invaluable information (and paper) handy.