Cold start; Climatologists waiting to see if La Nina conditions materialize

Body: 

GRAND FORKS, N.D. — The northern Plains are no stranger to fall snowflakes, but these past few weeks have delivered a heavy opening salvo that might signal a snowy winter ahead.

Grand Forks, N.D., streets and facilities manager Mark Aubol said the recent snowfall was one of the biggest autumn weather events he can remember over the past eight years or so. That's not to say he found it unusual.

"I'd say from (mid-October) on, we're in the region where we could get hit with any kind of snow," said Aubol, recalling years when his children would be faced with snow on Halloween. "Nothing's out of the norm there."

Even still, temperatures for this week are reading unusually cold for the season. When compared to last year's temperatures — when the Grand Forks office of the National Weather Service recorded a high of 72 degrees on Nov. 6, 2016 — they can feel outright jarring.

The weather service is forecasting highs in the teens and 20s and lows reaching zero through the weekend. There is a 40 percent chance of snow Wednesday, Nov. 8.

Beyond the usual conditions of a Midwestern winter, meteorologists and climate observers are now waiting to see if a global weather phenomenon known as La Nina, the cool-weather counterpart to El Nino, will mark this coming winter with even more cold and wet.

University of North Dakota atmospheric sciences professor Aaron Kennedy said he recently taught students about La Nina, a phase that makes up half of the El Nino-Southern Oscillation cycle that alternatively pulls and pushes heat between the atmosphere and a wide swath of ocean off the west coast of South America. That heat transfer creates different climate impacts across the globe and usually ushers in colder and wetter conditions for the upper Plains. That's not always the case, though.

"It's like having loaded dice," Kennedy said. "The probability is that we have colder, snowier conditions than usual, but that doesn't happen every time."

He said an example of that came just few years ago, when a La Nina pattern happened to coincide with a warmer winter on the northern Plains.

Nick Carletta, a meteorologist with the weather service in Grand Forks, also said the global phenomenon doesn't always manifest itself in the same way. As far as local weather goes, part of that is due to the continental climate experienced by much of the northern Plains, including North Dakota and parts of Minnesota. Another part is attributed to different mass oscillations besides La Nina-El Nino.

"There are a bunch of other ones, too," said Carletta, listing a series of counterparts. "I could go on and on, but those have an impact as well. If not La Nina, we'll likely have impacts from those as part of our outlook."

Meteorologists likely won't know until sometime in December whether La Nina is actually upon us. The meteorological community is now in a watch phase, Carletta said.

Though the status of the global climate system might be up in the air, it's already clear that recent weeks have been far more winter-like this year than they were a year ago. Carletta said the high on Nov. 6, 2016, was just one in a string of three days with temperatures higher than 70 degrees. That warm spell gave way to a gradual tapering to colder, more seasonal temperatures by the end of the month.

Kennedy chalked up the variable weather to the transitional nature of fall and the sometimes major weather swings of the upper Plains. He said it's not abnormal to get a heavy snowfall at this time of year, though he's wondering to what extent that snow will set the tone for the rest of the season.

"I think the big question is, does the snow stick around and we're basically in winter, or do we get a warmup that melts most of the snow?" Kennedy said. If it's the latter, "then we're back at square one."

From the looks of his data modeling, Kennedy thinks temperatures are going to stay colder for a while. Carletta thinks the weather might warm a bit after staying cold this week, but noted it's difficult to make accurate predictions any farther out than that.

Back on the streets, Aubol said the variable forecasts can require city workers to change gears mid-job, particularly in cases like last week when snow fell deeper than expected. But to him, that just comes with the territory.

"We can have a lot of fluctuation here at different times for any reason," said Aubol, who made sure to caution drivers to heed road conditions and asked homeowners to shovel off their sidewalks and hydrant accesses. "I think it frustrates people when we get the cold temperatures and snow at the same time, but when you get around the first of November, you've got to be expecting it."