La Nina to make an unwelcome return

With the weather phenomenon La Nina expected to gather strength this winter, we could be facing the same frustrating long, cold, wet spring in 2012 that occurred this year.

With the weather phenomenon La Nina expected to gather strength this winter, we could be facing the same frustrating long, cold, wet spring in 2012 that occurred this year.

“La Nina came in January, February, March and carried on (more or less) until July,” said David Phillips, senior climatologist with the Meteorological Service of Canada. “The best indications are showing that the weather on the west coast will be somewhere between this past year and two winters ago. So we expect the weather to be neutral on the west coast to the end of the year.”

But getting into winter, Phillips forecast that by January it could be colder than normal.

The last two winters were ones of extremes. In 2009/2010, we had a strong El Nino when it was warm and dry with such a remarkable lack of snow that it had to be trucked in from Manning Park for the Winter Olympics. In fact, January and February were the mildest ever recorded.

“It was warmer and dryer with very little snow,” said Phillips. “Vancouver had about 28 per cent of regular snowfall that year and temperatures were record warm.”

Fast track 12 months and La Nina had taken over. February 2011 produced record lows with strong outflow winds. On the 25th of that month those winds pushed temperatures down in the Chilliwack area to -22oC. Snowfall was 161.8 per cent above normal.

So, more of the same?

“If La Nina does not progress, it might be more like the previous winter of 2010,” explained Phillips. “But the problem this past winter was that La Nina came late and lasted well into spring. It actually didn’t go away. The Pacific Ocean water temperature was warmer but the atmospheric temperature was cooler. Last year snowfall was triple that of the previous year. Temperatures were cooler. My sense is with La Nina, if it does come back, it will be moderate.”

With the lingering La Nina, summer this year didn’t come until August.

“For the eleventh consecutive year, mean temperatures for August were above normal, a trend never previously having occurred since Chilliwack records started in 1895,” said Roger Pannett, Chilliwack’s volunteer weather observer for Environment Canada.

The National Oceanic and Atmospheric Administration (NOAA) stated on its website that La Nina conditions actually returned in August due to the strengthening of negative sea surface temperatures across the eastern half of the equatorial Pacific Ocean. The cool water changes the air temperature above it which changes air pressure, which changes wind patterns, which changes weather.

NOAA’s expectation is that La Nina will remain weak during the fall but strengthen with an increased chance of above-average precipitation across the Pacific Northwest later in winter.

Sea surface temperatures in the tropical Pacific Ocean are monitored by data buoys and satellites. NOAA operates a network of 70 buoys along the equatorial Pacific that measure sea surface temperature, currents and winds in the equatorial band. That data is added to information collected by polar orbiting environmental satellites and all the combined data is available to researchers and forecasters around the world in real time.

While La Nina is driven by Pacific Ocean conditions, its impact is global. It will ramp up storms in the Atlantic basin, threaten oil rigs in the Gulf of Mexico, trigger severe snowstorms, and cause extreme droughts such as the ongoing severe conditions in Texas and south-western U.S. It causes wetter monsoons in India, torrential rains and flooding in south-east Asia, yet warm and dry conditions along the coasts of Ecuador and Peru.

Given La Nina’s return, Phillips predicts that next spring’s weather could be a re-run of this year cool, wet season.