La Niña Strengthens further

The NOAA has released its annual winter outlook.

The Pacific Northwest should brace for a colder and wetter than average winter, while most of the South and Southeast will be warmer and drier than average through February 2011. A moderate to strong La Niña will be the dominant climate factor influencing weather across most of the U.S. this winter.

“La Niña is in place and will strengthen and persist through the winter months, giving us a better understanding of what to expect between December and February,” said Mike Halpert, deputy director of the Climate Prediction Center – a division of the National Weather Service. “This is a good time for people to review the outlook and begin preparing for what winter may have in store.”

“Other climate factors will play a role in the winter weather at times across the country,” added Halpert. “Some of these factors, such as the North Atlantic Oscillation, are difficult to predict more than one to two weeks in advance. The NAO adds uncertainty to the forecast in the Northeast and Mid-Atlantic portions of the country.”

This seasonal outlook does not project where and when snowstorms may hit or total seasonal snowfall accumulations. Snow forecasts are dependent upon winter storms, which are generally not predictable more than several days in advance.


Winter Outlook - Precipitation

NOAA Winter Outlook: Graphic NOAA


The beneficial effects of La Niña on the Indian monsoon have already been seen this year. But after the very cold winter in the Southern Hemisphere it remains to be seen if warm and dry conditions  are established in the South American summer now approaching.

From The Canadian Encyclopedia:

La Niña normally exerts much less of a global impact than El Niño, enhancing conditions that are more or less normal. Thus, under La Niña’s grip, normally wet Indonesia becomes wetter, and winters in Canada are often colder and snowier than normal. However, the weather associated with La Niña tends to be quite variable depending on such factors as its strength, the depth and geographic extent of the cool waters and the pre-existing atmospheric circulation. Among the normal weather effects of La Niña are wetter monsoons and flooding on the Indian subcontinent; torrential rains and floods in southeast Asia and northern and eastern Australia; cool and wet winters in southeastern Africa; and warm and dry conditions along the coast of Peru and Ecuador.

La Niña favours the formation of more and intense hurricanes in the North Atlantic Ocean. Three recent La Niña periods – 1988-89, 1995-96 and 1997-98 – were among the most active periods this century for Atlantic hurricanes.

North America typically feels the effects of La Niña during the winter and early spring. Wetter-than-normal conditions occur across the Pacific Northwest, British Columbia and Alaska. On the other hand, it delivers drier, warmer and sunnier weather along the southern tier of the United States from California through Texas to Florida. Northern states west of the Great Lakes generally experience colder and snowier winters. During La Niña episodes, there is also a greater risk of wildfires in Florida and dryness in the North American plains. The great dust bowl drought of the 1930s is thought to have been caused by a decade of La Niña-like conditions and was likely responsible, in part, for the severe drought in the American midwest in 1988.

During La Niña winters in Canada, the jet stream assumes its more normal mid-continental location. Because the mild air and cold air are never too far away, winters usually comprise alternating bouts of freezing and thawing. Overall, in Western and Central Canada, most La Niña winters tend to be colder than normal by 1 to 2°C, and snowfall amounts are greater than normal from the interior of BC to the St Lawrence Valley. During 8 La Niña episodes since 1950, 6 of the winters across Canada were colder than normal (2 were near-normal) and 7 were snowier than normal.


Global La Niña effects: graphic




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One Response to “La Niña Strengthens further”

  1. La Niña driving severe rains and floods in Brazil and Australia « The k2p blog Says:

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