The type of cold event that recently impacted most of the continental U.S. is already rare and becoming even more rare.
“How rare? Extremely rare, but we seem to be saying that about a lot of events these days, in terms of extremes,” Doug Kluck, Regional Climate Services director at the National Oceanic and Atmospheric Administration (NOAA), said in a media briefing last week. “Easily, this will go down as another billion-plus dollar event.”
Also, the impacts of the “very odd event,” as he described it, are still happening now, and require a great deal of study, he noted.
The cold event began with a Feb 12 departure from January’s seasonally warm temperatures on.
Most of the country saw a warm January — the ninth warmest in 127 years.
“We broke from that warm, dry pattern that we’ve been in and over the past week or so, we started experiencing this major cold event that has swept across the entire country,” said Becky Bollinger, assistant state climatologist for the Colorado Climate Center. “We’ve seen a lot of cold extremes throughout our entire north-central region.”
The worst of the cold was from Feb. 12-16, and involved much of the north central U.S. and points south as far as Texas. Through the entire center of the country, temperatures were more than 20 degrees colder than average, she said.
Due to a number of failures, the Texas power grid was failing, which caused rolling blackouts in that state, but across the central plains.
“We had to pull energy from many other parts of the grid, where they are used to having this kind of cold,” Kluck said. “It was hard to transfer energy for a number of reasons: It’s not as easy to do when it’s cold outside and there were failures in various systems.”
The southern third of South Dakota and down into Nebraska experienced temperatures 40 degrees or more below average. The northern two-thirds of the state, as well as North Dakota and Minnesota saw temperatures anywhere from 20-30 degrees or more below average.
There are a lot of questions about why the cold event happened, Kluck said.
Firstly, he said, there was a Sudden Stratospheric Warming (SSW) event on Jan. 5.
SSWs occur rarely, about six times per decade, when the polar stratosphere warms and the winds that normally flow from west to east around the pole weaken dramatically or even reverse direction, causing a corresponding breakdown of the polar vortex.
The polar vortex generally refers to the atmospheric circulation in the stratosphere. In polar regions, the bottom edge of the stratosphere starts about 5 miles above the ground and extends upwards to around 30 miles, according to www. climate.gov.
“The cold air from that event went into Eurasia and Asia and really got them very cold,” Kluck said. “Part of the repercussion of that was the weakening of the polar vortex, where the cold air loves to sit at the Arctic and spin around.”
The SSW allowed the cold air to move south, escaping the polar vortex, he said.
“The model started saying, America and North America, so we were able to pick up on that and start forecasting it about two weeks in advance,” Kluck said. “Our ability to detect and forecast these events much more than two weeks in advance is not great. It is very difficult to do.”
Climatologists knew it would get cold, but couldn’t determine how cold until a week or so out, he said.
“Also, there’s the Arctic Oscillation that often drives a lot of cold air into the eastern part of the U.S. when it’s in a negative phase,” Kluck said. “We had a whole bunch of negative-phase Arctic Oscillation when we were warmer than normal.
Bollinger offered a spinning top as an analogy of Arctic Oscillation caused by a weakened polar vortex.
When the vortex is strong, it’s got that tight spin,” Bollinger said. “Things like SSWs can kind of poke at it and the little poke on that top starts to cause a wobble effect. When you start the top wobbling, you don’t know where those waves are going to wobble down to, but you know they are going to come.”
A weakened polar jetstream may lead to outbreaks of cold, she said.
“One does not necessarily lead directly to the other, but often, it does,” Kluck said. “That’s one of the complicating factors with what we do in the climate world in terms of forecasting beyond a week or two.”
Though hard to forecast, these complex connections are a normal part of the earth’s climate, Bollinger said.
“While this cold was unusual, we don’t know that it is due to climate change,” she said. “But, with a warmer climate, we can still expect the possibility of cold like this happening.”
“For those who haven’t experienced this kind of cold during their lifetime,” Kluck added, “feel lucky because it’s rare and becoming more rare.
Also during the webinar:
• The cold has increased frost depth in the ground, which for areas with wetter soil, could lead to precipitation events running off and not infiltrating the soil;
• Streamflow indicators in the northern part of the region are not reporting, likely because they are ice-affected. Also, ice jams on the Missouri River are “not an immediate threat” due to the cold, but a fast warm up or a rain event could change that;
• Most of South Dakota is currently experiencing a moderate drought, as well as southern North Dakota and most of Nebraska. The western edge of South Dakota is in severe drought and the portion of the state along the Iowa border is in extreme drought. The northeast part of the state is experiencing only abnormally dry conditions;
• Snowpack, a good indicator for how much water is in the snow on the ground, is at trace amounts for much of the region;
• Soil moisture for South Dakota is about average, though the southeast corner of the state is showing areas of drier soil, as is most of Nebraska and western Iowa;
• The drought in the west and the typically windy days of spring will likely see many red flag warnings and high fire danger in the high plains.
• The current La Nina is expected to continue through the spring. With the probability of an El Nino low, neutral conditions are likely to prevail for the summer. There are few indicators at this time as far as forecasting the effects of the La Nina on temperatures for South Dakota, North Dakota, northern Nebraska or Minnesota;
• Areas that have been dry have an increased chance of continuing to be dry into March. At this time, the outlook for April and May are similar.