Contact:  Stephanie Kenitzer            FOR IMMEDIATE RELEASE
                                        3/26/96

VARIOUS CLIMATE FACTORS PLAYED IMPORTANT ROLE IN WEATHER PATTERNS DURING PAST TWO WINTERS

Much of the northern and eastern tier of the United States experienced near-record or record snowfall and extreme cold this winter, while areas of the Pacific Northwest were affected by severe flooding twice, and the southwestern and south-central states were abnormally dry and warm, according to a Special Climate Summary released today by the National Weather Service's Climate Prediction Center. These weather patterns were in many respects opposite to those observed during the 1994-95 winter season, the Climate Prediction Center said.

"A contributing factor to the differences between the two winter seasons was a transition from El Nino to La Nina in the tropical Pacific," said Gerald Bell, weather service meteorologist. "Another major contributor to these differences is simply the natural, short-term climate variability of global weather patterns."

In the Pacific Northwest, a series of strong winter storms triggered exceptionally heavy precipitation and two severe floods. In the southwestern and south-central United States, abnormally dry and warm conditions prevailed, with seasonal precipitation in this area totaling less than 50 percent of normal and temperatures averaging 2-3 degrees Celsius (4-6 degrees Fahrenheit) above normal. In comparison, the jet stream pattern last winter brought excessive storminess and precipitation to California, the Southwest and parts of the Plains, with relatively few major storms hitting the Pacific Northwest.

Along the northern tier of the U.S. and western Canada, winter temperatures averaged 2-5 degrees Celsius (4-10 degrees Fahrenheit) below normal, while several Arctic outbreaks swept over the East.

Much of these areas received 150-350 percent of normal snowfall, and approximately 15 major cities set new all-time seasonal snowfall totals. In contrast, much of the northeastern United States and Great Lakes region experienced significantly warmer-than-normal conditions and well below normal snowfall last winter.

The El Nino and La Nina phenomena are centered in the tropical Pacific and are well known contributors to the observed year-to-year climate variability. El Nino episodes are characterized by above- normal sea surface temperatures, while La Nina events are identified by below-normal sea surface temperatures in this area. During both El Nino and La Nina episodes, the normal patterns of tropical thunderstorm activity, winds, and sea-level pressure are disrupted throughout the tropical Pacific. In turn, these changes act to alter the atmospheric jet stream over the North Pacific, which ultimately affects the weather patterns and storm systems observed in North America.

Following the 1994-95 winter, there was a rapid decline in sea surface temperatures throughout the central and east-central equatorial Pacific as a prolonged warm episode ended. This was followed by the development of cold episode conditions during the late summer and fall, and a further strengthening of these conditions this winter.

In the middle latitudes, the effects of this transition were most evident over the eastern North Pacific. In this region, there was a pronounced northward shift of the jet stream and storm track, compared to an enhanced southward shift of these features during the past several winters. In turn, these changes influenced downstream atmospheric circulations, temperature, and precipitation patterns across North America.

The National Oceanic and Atmospheric Administration continues to monitor and predict the El Nino/La Nina episodes and their impacts on global weather patterns.

The Special Climate Summary, which also includes a summary of the notable weather events this winter, is available on NOAA's Climate Prediction Center World Wide Web Home Page, http://nic.fb4.noaa.gov.

  
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