Southern AERA Quarterly Activity Bulletin of The South Carolina Department of Natural Resources-Southeast Regional Climate Center
Volume 3, No. 4
By now, everyone has probably heard of El Niņo, as this weather phenomenon has become infamous due to the large amount of coverage it has received from the media this year. This is because the event that is upon us has been of unprecedented magnitude. Although you have undoubtedly heard of El Niņo, you may not understand exactly what it is, or how the El Niņo that is presently underway may effect our weather in the southeastern United States. The following is a brief synopsis as well as web site addresses that contain more information.
The El Niņo (also known as ENSO- El Niņo Southern Oscillation), is a combination of interrelated oceanic and atmospheric processes that occur every two to seven years. The Southern Oscillation refers to the flip-flop of atmospheric pressure between the eastern and western halves of the Equatorial Pacific that is closely related to El Niņo events. Although the Southern Oscillation and the El Niņo are closely related, an El Niņo may occur independently or at the same time as a Southern Oscillation. When the two coincide, however, the result is an extreme global atmospheric and oceanographic event.
The Peruvian Current is normally a cold current that moves northward along the coast of South America that causes an upwelling of cold, nutrient and oxygen-rich water that is conducive to dense concentrations of marine life. During an El Niņo, however, the relaxation of the trade winds may allow warm water to appear at the surface of South America. This warm water not only kills off marine life, but also affects the atmosphere directly above it producing convection, which can cause intense rainfall in a region that is normally dry.
In addition to the effects that are seen near the coast of South America, there are many other global impacts. These climatic aberrations are called teleconnections because statistical correlations have been found between these atypical weather events and the ENSO.
In the United States, ENSO teleconnections are seen more clearly in the winter. Intense rainfall has been recorded in the Southern US during El Niņo years. During severe El Niņo's, as is the one that is upon us, snow and ice storms as well as colder than normal temperatures have been reported. Although there is no way to be absolutely sure, as the ENSO we are now observing is more severe than any on record, this winter should prove to be a cold and wet one.
Let it Snow!
Winter brings different types of precipitation all over the world. Sometimes we see rain, sometimes we see snow, and other times we see freezing rain or sleet. Each of these different types affects our daily lives each winter season. This activity explores the different types of precipitation during the winter season.
Different Types of Winter Precipitation
* Snow - a solid form of precipitation composed of ice crystals in a complex hexagonal form. Actually, much of the precipitation that reaches the ground begins as snow. But only in winter months, when the freezing layer is much lower to the ground, do snowflakes have a chance of survival.
* Flurries - Snow falling from developing cumulus clouds. These are usually light showers that fall intermittently for short durations and produce only light accumulations (usually not measurable in the South).
* Snow Squall - A more intense snow shower. These are brief, but heavy falls of snow that are comparable to summer rain showers. These actually fall from cumuliform clouds. A more steady and continuous snowfall accompanies nimbostratus and altostratus clouds.
* Blizzard - A weather condition associated with low temperatures and strong winds greater than 30 knots. These winds contain large amounts of fine, dry, powdery particles of snow.
* Sleet - When falling snowflakes come into warmer air, they begin to melt. Then if it falls through the deep, subfreezing surface layer, the partially melted snowflake, or cold raindrop, turns into a tiny ice pellet, called sleet. Sleet bounces when it strikes the ground and producing a tapping sound when it hits glass or metal. (This is not small hail.)
* Freezing Rain - When the cold surface layer beneath a cloud is too shallow to freeze raindrops, the drops reach the surface as supercooled liquid drops. When the liquid strikes a cold object, the drop spreads out and freezes. This is freezing rain. Once it covers surfaces and objects, it is sometimes referred to as glaze.
* Snow Grains - Small, opaque grains of ice. This is the solid equivalent of drizzle. Snow grains fall in small quantities from stratus clouds.
* Snow Pellets - White, opaque grains of ice. These are brittle, crunchy, and they bounce or break apart upon striking a hard surface. Snow pellets fall from cumulus congestus clouds.
1. Explain the difference between snow grains and snow pellets.
2. What is the difference between sleet and freezing rain?
3. Describe weather conditions associated with a blizzard.
4. Describe the type of clouds associated with flurries? Snow squalls?
5. When can snow occur in the upper levels of the atmosphere?
6 - 8. To the right side of each vertical temperature profile, write which kind of winter precipitation you'd expect in each profile.
9. On March 12, 1993, an extremely severe, late winter storm formed in the western Gulf of Mexico and then moved northeastward. The center of the low pressure area passed across SC, battering the entire state with damaging winds, extremely low atmospheric pressure, very cold weather, and precipitation varying from 11.5 feet in the mountains to snow flurries in the southeast portion of the state. Almost the entire eastern seaboard was affected, from the Florida panhandle to Central Massachusetts.
* Choose one of the following states that was affected by the "Winter Storm of the Century" on March 12-14, 1993, and use references such as the Internet, Farmer's Almanacs, recent weather books, or encyclopedias to assess the amount of damage that was done in that particular state. Research and then report to the class on what you found.
Alabama Louisiana North Carolina Connecticut Maryland Pennsylvania Delaware Massachusetts Rhode Island Florida Mississippi South Carolina Georgia New Jersey Virginia Kentucky New York West Virginia
Southern AER is a quarterly publication of the Southeast Regional Climate Center. Funding is provided by a grant from the National Oceanic and Atmospheric Administration.
Internet Resources On Winter Precipitation