BROOKINGS — Starting this weekend and going through next week, stand by for heavy rolls — overnight and for about 10 days Brookings area residents can expect overnight double-digit below-zero temps and daytime single-digit above-zero temps.  

“The atmosphere patterns over the North American continent are changing over the Dakotas and Minnesota,” explained Laura Edwards, South Dakota State University Extension state climatologist based in Aberdeen. “We’re going to see very cold air come down from northwestern Canada, a northwesterly flow, … and generally speaking drier air.”

And look for the tough weather to linger awhile, until Feb. 7. “Much colder than average up here in the north central states,” she added. “It looks like it’s going to sit over us for awhile.”

However, she doesn’t expect the brutal cold to bring “active weather, (and) probably quieter as far as precipitation goes,” she said. She added, “Meanwhile, wetter weather patterns will be playing out in the west and the east. We’re somewhere in the middle there, as far as precipitation goes.”

But does this weather phenomena warrant being called a “polar vortex”? “I’ve heard that word thrown around a little bit this week,” the climatologist said.” I guess you could call it that — very cold air coming down from the polar regions. I don’t know if you classify it as what people know as a typical polar vortex; but certainly it’s very cold air coming down from northwestern Canada.” (A National Weather Service website shows a polar vortex as: “Cold air and low pressure near the (north) pole; while polar vortexes are always present at both poles, when the one in the north meets the jet stream cold air surges south into the U.S.)

There will be “some breezy condition” over the next few days as the temperatures go from warmer to colder, but only one day could be classified as windy.

So when all of the above is over and we start looking to spring, whenever it comes, what should we look for?”

Gazing into her crystal ball … ?

Edwards cited a couple of things to consider for spring, especially tied to the potential for flooding: “La Niña conditions are in effect colder than an average winter.” During a La Niña season, there are cooler water temperatures in the Eastern Pacific Ocean near the equator. The cooler water impacts weather in the U.S. especially during December through February.

“What we saw in December and now again in February is more consistent with a La Niña pattern all across the cpintry, both for temperature and precipitation. In March or April, the La Niña pattern will fade away. It’s less a player in our spring and summer climate.” So what could come next?

“The snow pack is holding 2 to 4 inches of water right now, a little less in the James River Valley,” Edwards explained. She called the snow pack “a natural reservoir” that “will hold the water as long as it stays cold.”

“If the weather stays colder longer and that snow doesn’t melt until late March or early April, the risk of flooding can be a little higher,” she noted. “Generally, if that snow pack is still around, then what happens is we often get a really warm period and that snow melts really quickly. And that’s when you can get some flooding.”

A heavy rain could also rapidly melt the snow on the ground.

The National Weather Service’s River Forecast Center looks at eastern South Dakota, “because we do see so much flooding here, across this region.”

Continuing, the climatologist noted that “frost in the soil is not very deep right now.” Trace that to the coincidence of the weather turning cold in December and the arrival of snowfall.

“The ground got cold for awhile but then it got insulated very quickly with a relatively deep snow pack,” Edwards explained. “That prevented the frost from getting very deep.

“So that’s good news; because that soil is more likely to thaw out faster and be able to take out all the moisture from the snow melt. All of this comes down to the timing being right.

“The situation there would be that if we have a nice slow melt, a gradual thawing of things, that’s probably the best situation we could have – for the farmers planting and to reduce the risk of flooding.”

Edwards did note that “we are carrying over some dry soils from the last couple of years, actually, of drought. So there’s a lot of the capacity in the soil to take up that moisture. Again assuming that we have a nice easy thaw season and it doesn’t come too fast.”

She did note that to date “we have had a very warm January for Brookings so far, about 6 degrees (Fahrenheit) above average. It’s going to be kind of a shock to the system for February, when we see very cold temperatures next week — which could be 10 to 20 degrees below average for this time of year. We’re making a real quick turnaround.”

As for snowfall this season: it’s just over 20 inches. Average for an entire winter season is about 27 to 28 inches. She added: “A very snowy December brought about 14 inches, most of it in the last couple weeks.”

Contact John Kubal at jkubal@brookingsregister.com.