As hurricane season comes to a close and the cool Fall weather begins to make for nice scenic backgrounds, we look ahead to what may be in store this Winter. Long-term forecasting of more than a month in advance is very difficult and is still yet not fully understood. Of course when trying to develop these forecast, the margin for error is quite large. However, numerous meteorologist make these long-term predictions based off of key components that drive our global weather patterns from month to month. These components are known as oscillations and come from pressure differences around the globe.
First meteorologist look at the current weather patterns and try to understand the reasons why the hurricane season was so busy which may lead to some answers to what might come of the Winter months. The main driver for our weather this hurricane season is known as La Nina. La Nina is a cool phase of the ENSO(El Nino Southern Oscillation). This oscillation is one of those driving forces behind global weather patterns throughout all times of the year. As we look towards the Winter months, all indications are that the oscillation will be in a cool phase known as La Nina. La Nina occurs when trade winds increase off the Pacific coast of South America leading to the upwelling of cooler waters from below and creating a pocket of cool water along the equator. Since the Western Pacific is mostly warm and moist the air pressure is usually lower than normal as warm air always rises. This cool pocket leads to higher pressure over the Eastern Pacific Ocean; thus, understanding the fact that winds blow from areas of high pressure towards low pressure you realize the atmosphere has created a circulation as the warm air over the West Pacific rises, while the cooler air over the East Pacific moves along the Equator in a westerly direction to fill the hole left by the rising air.
How does this cause our weather to change?
The weather patterns around the entire world are always trying to balance themselves out due to pressure differences. A perfect atmosphere would be an atmosphere with no temperature gradient creating no differences in pressure from place to place. Unfortunately, that has never been the case and will never be the case due to the Earth’s number one source for warmth, the Sun. If you can remember from the paragraph before, the cooler waters along the equator in the Eastern Pacific Ocean lead to high pressure because cold air weighs more than warm air. This high pressure has a large scale effect on the weather pattern in North America. The high pressure becomes very strong during a La Nina event and blocks storms from riding across the Pacific Ocean and moving across the United States. Instead these storms ride up and over the high pressure only to move into Canada and just skirt the Northern United States. This can lead to drought conditions across the Southern United States but it also limits the amount of cold air that makes it into the United States. However, the pattern can be variable and given that much of the cold air in Siberia is pushed into Canada by this high pressure over the Pacific Ocean, major cold snaps can occur during La Nina years. Overall the cold snaps will be in between very warm periods making for a warmer than normal Winter across the Southern United States.
Already Louisiana is feeling the effects of La Nina with drought conditions becoming very prominent across the state. October has been the driest month of the year and Winter has yet to even begin. Most people living in the Deep South won’t mind the warmer than normal Winter; however, a dry pattern is not something people want to see at this point. My only advice to you is start doing a rain dance because La Nina has us in her full grasp.
-Zack Fradella
