The National Oceanic Atmospheric Administration's (NOAA) Climate Prediction
Center has officially declared a La Nina Advisory, as of Nov. 9.
"This means that La Nina conditions are observed and expected to
continue," said Laura Edwards, SDSU Extension State Climatologist.
NOAA observes La Nina conditions using sea surface temperatures in the Pacific
Ocean, Edwards explained. "For La Nina, ocean temperatures are cooler than
average near the equator in the Pacific Ocean, which can alter jet streams and
storm tracks," she said.
Historically, La Nina has brought colder than average temperatures in winter
for South Dakota. "There are varying strengths of La Nina, from weak to
strong. Overall the colder temperatures are fairly consistent in any La Nina
winter," Edwards said. "What is more variable is snowfall."
In weak La Nina events, there has historically been above average snowfall in
the Northern Plains states. In strong La Nina events, this is not usually the
case.
For our winter season ahead, Edwards said a weak La Nina is expected.
"Thus the climate outlook shows an increased chance of above average
precipitation," she explained.
This potential increase is snowfall is more likely to occur in mid- to late
winter, or around January and February of 2018.
Despite the very dry November, there was recently a large pattern shift in
early December, which is now starting to look more like a typical La Nina
pattern.