La Nina Discussion... La Nina is defined as cooler than normal sea surface temperatures in the eastern equatorial Pacific Ocean. La Nina is the opposite of El Nino. La Nina occurs when the water temperature in the equatorial Pacific ocean cools dramatically , while El Nino occurs when the water temperature in the equatorial Pacific ocean warms significantly. During many years the equatorial Pacific ocean experiences surface temperatures near normal. The normal temperature range for the waters in the eastern equatorial Pacific ocean is in the 60s and 70s degrees Fahrenheit. However, water temperatures in the western and central equatorial pacific ocean exceed 80 degrees Fahrenheit. El Nino episodes occur when the warm waters of the western and central equatorial Pacific expand to cover the entire equatorial Pacific ocean region, due to weakening trade winds, causing water temperatures to warm significantly above normal over the entire equatorial Pacific. La Nina episodes occur when the easterly trade winds increase and upwelling of cold water along the region occurs, causing water temperatures to drop significantly below normal. La Nina and El Nino episodes occur because of interactions between the ocean surface and the atmosphere in the equatorial Pacific. Changes in either the atmosphere or ocean can directly impact the other...therefore altering climate patterns across the world. An example would be the altering of the upper level jet stream which carries weather systems around the globe.

Forecast Discussion... The NOAA's Climate Prediction Center (CPC) has predicted that the nation will continue to experience a La Nina episode this coming winter and spring. The predictions call for a moderate to strong La Nina event. Official Long Range Temperature and Precipitation Forecasts and Advisories concerning this La Nina episode for the entire nation are supplied on a monthly basis by the CPC. The latest CPC Long Range Forecasts for the coming winter and spring imply that the Great Lakes region (including the Western New York area) and the Northeast part of the country will experience
cooler and wetter conditions as compared to normal during the winter and spring seasons. Typically, stronger La Nina events will bring near normal temperatures (map) and near normal precipitation (map) to our area in the winter and below normal temperatures (map) and above normal precipitation (map) in the spring.

Long Range Forecast for Western New York (Buffalo and Rochester Metropolitan Areas)...It has has been determined that 15 La Nina episodes (1904, 1908, 1910, 1916, 1924, 1928, 1938, 1950, 1954, 1964, 1970, 1973, 1975, 1988, 1995) of varying degrees of intensity have occurred during the past century. A local analysis of weather conditions during the winter and spring seasons, during the 15 La Nina years, was done for both the Buffalo and Rochester areas to determine what weather conditions could be expected across the area this coming winter and spring. Local analysis on both the Buffalo and Rochester area La Nina year temperatures (click here for Buffalo or click here for Rochester) suggest that during the winter (December-January-February) period, temperatures can be expected to be just slightly above the 30 year normal. However, during the spring (March-April-May) period, temperatures can be expected to be below normal. This would suggest that in La Nina years the Western New York area can expect to have a longer then usual "winter" season (one which would extend into the springtime). This is consistent with a La Nina episode (developing a cooler than normal pattern through the winter and spring). As compared to El Nino years, both winter and spring temperatures are significantly colder during La Nina episodes. Local analysis on both the Buffalo and Rochester area La Nina year precipitation amounts (click here for Buffalo or click here for Rochester) suggest that that during the winter period, precipitation can be expected to be above the 30 year normal across the Buffalo area, but below normal across the Rochester area. This would result in generally near normal condtions across the entire Western New York area. However, during the spring period, both areas can expect precipitation to be above normal. This would suggest that in La Nina years the Western New York area can expect to have a prolonged wet period through the winter and spring seasons. This is consistent with a La Nina episode (developing a wetter than normal pattern through the winter and spring). As compared to El Nino years, both winter and spring precipitation amounts are significantly greater during La Nina episodes. Analysis of snowfall amounts (click here for Buffalo or click here for Rochester) indicates that the Buffalo area experiences a slightly greater snowfall amount during a La Nina  episode as compared to the 30 year normal, and significantly greater amounts than during an El Nino episode. The Rochester area experiences a lesser snowfall amount during La Nina episodes as compared to normal, however a significantly greater amount than during El Nino episodes. The overall result would be for near normal snowfall conditions across the entire Western New York area.

Summary... A La Nina epsiode is currently occurring across the United States and is forecast to continue through the coming winter and into the spring of 1999. A moderate to strong La Nina event is forecast. The Western New York population should prepare for temperatures to be around the seasonal normals during the winter with cooler than normal temperatures during the spring, making the "winter season" feel like it is lasting a longer than usual.  Residents can expected near normal precipitation condtions to occur across Western New York during the winter with an increase in amount and frequency of precipitation during the spring. Western New York is known for its snowfall and the area should be prepared for amounts generally around seasonal normals, however it  should be noted that even though snowfall amounts are expected to be near normal, on a whole across the area, amounts will be significantly greater than  amounts received across the area last winter season. Since a moderate to strong La Nina event is predicted the above forecasts may be enhanced to a greater degree.

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