Weathering the possibilities for winter

As I finish this column it is snowing outside and a look at the radar indicates a classic “lake effect” fetch driven by winds from the southwest has set up over the north county. I recently read a book by a Syracuse University professor and was surprised to find out that prior to weather radar no one knew for sure that there was such a thing as lake effect snow. In my lifetime our knowledge of the weather has expanded greatly but it is obvious we have a lot more to learn.

We have all heard the terms El Nino and La Nina and know that they have an impact on our weather. Not as many of us may have heard of the NAO or the North Atlantic Oscillation that also impacts our weather. Now with meteorological winter starting Friday I realized I needed to get a better idea of why these conditions occur and what they mean for winter weather in Chautauqua County.

El Nino and La Nina are two opposing climatic conditions that change normal weather patterns off the Pacific coast of South America. Each episode generally lasts about 12 months and typically occurs every two to seven years. However, both conditions can also last as long as four years.

Under normal conditions the trade winds blow from east to west along the equator. These winds carry warm, moist air towards the western Pacific which in turn keeps the waters off South America cool. This is called the neutral phase.

During an El Nino the trade winds weaken, and warm water is pushed east towards the coast of South America. These warmer waters cause the Pacific jet stream to move south and the Polar jet stream to weaken and retreat north. For Western New York, an El Nino usually means warmer and drier-than-normal conditions in winter

La Nina is essentially the opposite of El Nino. The trade winds strengthen, and the east central parts of the Pacific become even colder while the western pacific becomes warmer and experiences more rainfall. The Cold waters in the Pacific push the jet stream northward. La Niña winter seasons tend to be snowier than average in the Great Lakes, and upstate New York.

So, what about the North Atlantic Oscillation? The NAO describes large regions of relatively high pressure centered over the Azore islands and low pressure centered over Iceland. The NAO describes the relative changes in pressure between these two regions as either positive or negative.

To understand what happens with a positive NAO imagine Route 60 late at night. With few cars and few accidents traffic moves quickly from place to place. This is what happens during a positive NAO with lower than normal pressure over Iceland and higher that normal pressure over the Azores. Storms move quickly with less impact on local weather. In Western New York the positive phase of the NAO generally brings higher air pressure, a condition associated with fewer cold-air outbreaks and decreased storminess.

A negative NAO is the reverse of a positive NAO. Again, imagine Route 60 on a Friday afternoon with traffic heavy. Add to this a stalled car and an accident or two causing traffic to be stopped or slowed to a crawl and needing to be diverted. When the NAO is in the negative phase there is higher-than-normal pressure over Iceland and lower-than-normal pressure over the Azores. In Western New York the negative phase of NAO generally brings lower air pressure, a condition associated with stronger cold-air outbreaks and increased storminess.

This winter according to the Weather Bureau during the months of December, January, and February we can expect El Nino and a positive NAO to usher in meteorological winter on December 1. Based on this scenario we can expect temperatures to trend warmer than average and precipitation to be lower than normal this winter. However, the bureau hastens to add that this is but one possible outcome and that others could occur. That could best be described as hedging your bets.

The Earth’s weather systems are magnificent, interconnected, and complicated examples of nature at work. The development of El Niño and La Nina events are linked to the trade winds. The strengthening and weakening of the trade winds is a function of changes in the pressure gradient of the atmosphere over the tropical Pacific caused by something called the Southern Oscillation which refers to changes in sea level air pressure patterns in the Southern Pacific Ocean between Tahiti and Darwin, Australia. Further The NAO is affected by the interplay of the Polar low and the Azore High. Based on this one has to wonder how in such an intertwined climatic system how climate change can be linked solely to the actions of mankind. We have gained great understanding of our weather and climate, yet it is obvious that we have much more to learn.

Finally, if this winter turns out to be something like the winter of 1976-77 with lots of snow and frigid temperatures, blame those people at the Weather Bureau and not me.

Thomas Kirkpatrick Sr. is a Silver Creek resident.


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