Post by Bennett D. Ebberly on Oct 4, 2003 11:44:02 GMT -5
El Nino and The Coming Fall/Winter
8AM EDT, September 27, 2003
By WeatherBug Meteorologist, Justin Consor
As the first frosty air masses descend into the U.S., attention is turning to the forecast for the upcoming fall and winter.
One factor that has had a large impact is El Nino and La Nina. El Nino is defined as a periodic warming in the eastern and central Pacific near the equator. El Nino conditions usually favor a warm and dry winter in the northern U.S. with cool and wet conditions in the south and especially in California.
La Nina is a cooling in the eastern and central Pacific near the equator. Its effects are typically opposite - cool and wet in the northern U.S. with warm and dry conditions in the south.
Currently, as the image in the upper right corner shows, water temperatures in the equatorial east Pacific between the international dateline and coast of Peru are near normal. This pattern is known as neutral conditions, with neither El Nino nor La Nina present.
Forecast models indicate the neutral conditions will persist through the winter. This means that other climate factors - such as water temperatures in the north Pacific and north Atlantic, soil moisture and snow cover - will play a larger role.
The persistent drought and very low soil moisture in the West would favor less cloudiness and warmer than normal conditions unless other factors cause a reversal of the drought.
Hurricanes Fabian and Isabel may also play a role several months down the line, as they have altered the water temperature profile in the Atlantic.
Fabian and Isabel cooled a large stretch of the central Atlantic from north of Puerto Rico up toward Bermuda and westward to off the southeast U.S. coast, but also helped to transport heat and warm water to high latitudes between Canada and Greenland.
Factors besides El Nino also played a large role last winter. A moderate El Nino was present during fall 2002, but it became weaker as winter 2002-03 progressed.
Early snow cover over eastern Canada and the northeast U.S. as well as very warm water temperatures between Greenland and eastern Canada encouraged a large blocking high pressure to develop at high latitudes, forcing cold air masses into the heart of the eastern U.S.
Similar conditions have developed this week, allowing a record-breaking cold air mass to plunge toward the Midwest and northeast. If this pattern continues into October it could signal an early winter.
There are signals in the overall pattern this fall that favor cold air to cover a wider area than last year with the bone-chilling air masses most frequently plunging into the Rockies and Plains. Last year`s cold focused in the northeast.
This report is from www.weatherbug.com/