Atmosphere And Weather

How El Nino Affects the Weather



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In order to understand how El Nino affects the weather, it is first helpful to understand what it is. Considering the number of misconceptions about El Nino, it would seem that this is hard to do. In truth, it really isn't.

On the western side of America, there are two strong currents. One transports heat in the Pacific Ocean toward the poles. The second transports cold water from the poles toward the equator. Normally, the warm current lies well off the coast, forcing colder water closer to shore. This encourages stable weather and temperatures, and is responsible for keeping the coastal areas damp but relatively constant in temperatures.

Periodically, the warm current swings in much closer to the continental shelf of North America while moving away from the coast of South America. Some people think of it as an unusual warming, but it really isn't. The warm current is always there; it is merely a greater distance off the coast under normal circumstances. However, it does often get closer to the surface of the ocean as it shifts, as well.

This has a profound effect on weather. As in the gulf of Mexico, warm water near the surface means that more water is evaporated, which generates more energy, and it turn produces more storms. Since there is no buffer of colder water to prevent the energetic moisture laden storms from coming inland, severe weather can lash much of the western US. This can mean above normal early year precipitation, more summer thunderstorms than usual, and since the pattern usually lasts for in excess of a year, greater quantities of snow further inland.

The disruption doesn't just impact the most western states, either. Especially in winter, the powerful warm air mass pushes cold air coming from the Gulf of Alaska much farther inland. Cold air that would normally grip British Columbia, Washington, Oregon, and Northern California is pushed hundreds of miles further east. The result is that while the extreme western states have a warmer and wetter winter, much of the middle of the country is plunged into suddenly intensely cold air.

Temperatures plummet, generally earlier than cold temperatures usually strike, but with the cold dry air, precipitation levels in the middle of the country also drop. Also, when the cold dry air meets the much warmer and moister air moving north from the Gulf of Mexico, enormous storms are produced. This can generate large numbers of tornadoes, freezing rain, or snow storms in areas of the country not known for snowstorms, especially early ones.

The El Nino affect also brings the potential for flooding in those areas that are moister and warmer than normal. For instance, early in this decade, an area of south eastern Oregon was deluged with nearly three inches of rain in roughly four hours. For some parts of the country, this may not be a great amount of rain. However, this was an area of Oregon known as the Oregon High Desert, where yearly precipitation totals will seldom top 10 inches, counting snow.

The ground, which was already abnormally wet, couldn't hold the water. The result was flooding of roads, rivers, the town, and fields. One underpass contained over 18 feet of water since it couldn't drain off fast enough into the already swollen lakes and rivers, and this was all in an area that rarely floods.

The weather problems don't stop there. Since El Nino forced much warmer air over the area, though the rainfall early in the year was high, snowfall wasn't except for further east. The snow melted before it reached the ground and fell as rain. The problem is that without a snow pack, by early summer the area was already drying out, creating near drought conditions, while in areas that got above normal snow fall amounts were having to deal with flooding from the melting snow.

Places that receive more moisture than normal also tend to have a greater number of thunderstorms, since there is greater evaporation from the increased amount of water.

You might ask if a shifting ocean current can really cause all of these weather changes, and the answer is yes. Winds and storms are all primarily driven by variations in ocean currents. The problem is that while many people are guessing at what causes El Nino, nobody knows for sure. We can detect it. We know how it changes weather patterns and causes weather. But we have no idea what the real cause of the shifting current is.

Knowing how it affects the weather, though, can at least give us an idea of what to expect and to prepare for.

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