This winter is likely to be near or among the top 33% of the coldest winters in last 106 years, according to Salomon Smith Barney meteorologist Jon Davis. Based on current weather variables, Davis concludes in his “2001-2002 Winter Outlook” that temperatures this winter should be quite similar to the average temperatures last winter, which ranked 24 on a scale of 1-106 with 1 being the coldest.

“The odds do not point to an exceptionally cold winter such as one out of the top 10 coldest, but that is not totally out of the question,” Davis said in his report. “One outcome that we believe is out of the question is the possibility of an extremely warm winter…Our research indicates that the potential for this winter to be even in the warmest third of historical norms (72-106) is very slight.”

Davis believes that the upcoming winter will be similar to last winter, and will continue the trend reversal from the record warm winters of the late 1990s. The November-December period last winter was the coldest such period in the last 106 years. He doesn’t expect the early portion of this winter to be that extreme. But unlike the second half of last winter, which was milder, with January ranking 58 and February ranking 56 out of 106 winters, Davis believes that the second part of the 2001-02 winter (January-February) will be much colder.

Several factors point to this winter being colder than normal. One is a negative Pacific Decadal Oscillation (PDO) and another is a neutral El Nino/La Nina. El Nino is a period of warmer-than-normal seas surface temperatures (SSTs) in the Equatorial Pacific, and La Nina is a period of colder-than-normal sea surface temperatures in the same region. When SSTs are neither warm nor cold, they are said to be neutral. Currently SSTs are maintaining a neutral state in the Pacific Ocean.

In addition, there currently is a “textbook” negative (cold) phase of PDO, which is a long-term climatic cycle with phases that last two or three decades. These phases involve changes in sea surface temperatures in the Pacific Ocean and are related to the short-term El Nino/La Nina phenomenon. A positive PDO is an “El Nino enhancer” and a “La Nina suppressant,” Davis said. A negative PDO is an “La Nina enhancer” and an “El Nino suppressant.” The oscillation consists of large-scale changes in sea surface temperatures. In the 1980s and 1990s, there was a positive PDO and now the PDO has switched to a negative phase.

As a result, the United States “should not experience the high incidence of record warm winters that characterized the 1990s,” said Davis. “This does not mean that the new decade will feature 10 cold winters in a row. What it does mean is that the chance of the United States having a repeat of the late 1990s (that is, three consecutive warm winters) is exceedingly unlikely.” The probability points toward more normal winter weather ahead, he said. In the near term, however, it points toward another cold winter.

The neutral El Nino/La Nina also indicates colder weather this winter. “SSTs this year are very similar to last year going into the winter heating season,” said Davis. “This points more toward frequent intrusions of arctic air this winter, which would lead to a more normal or colder-than-normal winter.”

Another factor, Davis examined, is the presence of “cold pooling.” It is the time when cold air begins to build up across the polar regions and snow and ice begin to expand southward, which will allow the jet stream to pick up the cold air and drive it across the continent during the winter. Last year there was an early build up of cold air across the northern regions, which set the stage for a very cold early winter. This year there was a steady pooling early but a slight decrease since August. Some northern “source” regions, however, have been showing colder than normal temperatures recently.

As a result, all the factors are in place for another colder-than-normal winter, according to Davis. Based on current SST patterns, he believes the strongest bias toward cold, and the coldest temperatures will occur in the central and eastern United States, particularly in the early part of winter.

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