Weather variability and climate both contribute to winters in southeast Michigan. In this week's "Issues of the Environment," WEMU’s David Fair explores what kind of winter we may see and what factors play into the forecasts with University of Michigan professor of Climate and Space Sciences and Engineering, Dr. Richard Rood.
* Winter weather in southeast Michigan is predictably cold, but it is also highly variable which can lead to the perception that it is unpredictable. Factors that get tossed around are La Nina/El Nino, Arctic Oscillation (related to the polar vortex), and climate change. These elements each contribute to weather patterns in our area, but with varying importance.
* Part of the reason weather is difficult to predict in Michigan has to do with the uncertainty of focusing on a relatively small region surrounded by massive lakes. As the area gets smaller, the uncertainty gets higher.
* In Michigan, La Nina (at this date, the 2016-17 winter pattern) tends to be wet in the winter, and perhaps some tendency towards cooler. However, both of these signals are weak. La Nina gets a lot of press, but may not be as impactful as other factors.
* The largest variability of winter temperature in Michigan due to the Arctic Oscillation, another pattern of variability. La Nina might be viewed to actually "act" through Arctic Oscillation.
* Arctic Oscillation is connected to the polar vortex, the predominant force shaping winter weather in southeast Michigan for the past several years.
Like cold and snow? Hate it? Either way, there’ll be something for everybody this winter, according to meteorologists. While this winter season is expected to be harsher than last, that isn’t saying a lot.
In October, the National Oceanic and Atmospheric Administration's Climate Prediction Center issued the U.S. Winter Outlook. Rich Pollman told the Free Press what that means for Michigan. "That’s not a huge limb to go out on since last year was one of our warmest winters on record," Rich Pollman, warning coordination meteorologist for the White Lake Township office of the National Weather Service, said of forecasting harsher weather this December, January and February. He said there is a likelihood of above-normal temperatures across the southern half of the U.S. and a likelihood of below-normal temperatures from the Upper Peninsula back to North Dakota, South Dakota and Montana.
Those extremes — above-normal temps to the south and below-normal temps to the north — leads to a more active storm track for the central part of the country, Pollman said.
“What that means for us is that we’re looking at a better likelihood of above-normal precipitation and temperatures that are going to be highly variable across lower Michigan,” he said. "It wouldn't be surprising if some storm systems brought temperatures in the 50s with rain and then an arctic air mass could plunge in with lake effect snow."
The Climate Prediction Center gave Metro Detroit equal chances of all of these this winter: normal temperatures, below normal or above normal. (Expect similar weather for our listening area.) “We’re going to have the highs and the lows. We’re going to have warm air and cold air, both,” he said. "We’re going to have rain, we’re going to have mixed precipitation, and we’re going to have snow. We’re going to a have a little bit of everything this winter.”
Players in our Winter Weather
Predicting winter weather in our area is far from an exact science, and there are several reasons why. Dr. Rood pointed out that the size of an area is inversely correlated to the likelihood of an accurate prediction. From a weather prediction perspective, southeast Michigan is a speck on the globe, so it is hard to know with certainty if winter will be wetter, snowier, warmer, etc.. than average. Still, we try.
The past couple of winters have been deeply influenced by the polar vortex, and even if the La Nina pattern comes to pass, that could still be the case this winter. The polar vortex in heavily influenced by Arctic Oscillation. Never before measured variability has been found in the Arctic over that past decade, most likely due to climate change. So, even if it was possible to absolutely predict the historically expected weather based on models, climate change could alter everything.
Climate predictions are full of will they/won’t they suspense, like this year’s La Niña. In September, the National Weather Service canceled its months-long lookout for the climate phenomenon—which, as a counterpoint to El Niño, is associated with cooler overall global temperatures. Then, in early October, the agency reversed. Its Climate Prediction Center predicted a 70 percent chance of La Niña forming and folded that prediction into its Winter Weather Outlook. If true, that means the next few months will be warm and dry in the southern half of the US; wet and cool in the north.
A La Niña requires months and months and months of persistently cool sea surface temperatures in the equatorial Pacific—and—colluding atmospheric conditions, like stronger than normal trade winds.
La Niña and El Niño are part of the same climate cycle. And like all things climate, they begin with the sun. Solar energy heats the ocean’s surface, creating convection—wind. The Earth’s rotation (via the Coriolis effect) makes those winds blow from east to west. Trade winds. They, with help from giant subsurface waves, push the warm surface water westward against the island clusters of Indonesia and Papua New Guinea.
“There’s a slow buildup of warmer than average water under the surface in the western tropical Pacific,” says Anthony Barnston, chief forecaster for the International Research Institute for Climate and Society at Columbia University. “If you build up enough it will spill over into eastern tropical Pacific.” When the spillover happens, the normally cool eastern Pacific becomes unusually warm. The convection slows down, and the trade winds fade, or die. From there, global weather havoc—El Niño.
In all things, balance. La Niña is the yin in the tropical Pacific tajitu. Sometimes, as an El Niño drags on, giant subsurface waves begin to reflect off Indonesia and the other islands. The water there is tepid, drawn in to replace the warm stuff that went east. If the subsurface waves push enough cool water to overcome the balmy El Niño blob, you’ve got La Niña conditions. (Note: La Niñas don’t just form after El Niños.)
“But if the ocean cools off without the atmospheric component, you can’t have a La Niña,” says Barnston. That means the trade winds have to kick up a notch or so. “That correlates with things like shifts in tropical rainfall patterns, sea level pressure, and upper atmospheric winds.” And those drive phenomena like hurricane formation and drought.
For the past several months, a crucial area of the central tropical Pacific has been cold enough for La Niña, but the trade winds have been normal. The people who keep track of La Niñas and El Niños work at NOAA’s Climate Prediction Center. The crucial area they watch is a rectangle about the size of the US along the equator between the International Date Line and South America Pacific. It is called the Nino 3.4 region.
For now, a weak La Nina is expected, but, on the whole, this may not be all that important to weather in our listening area.
La Nina/El Nino and Climate Change?
Lest we not forget, 2016 will likely be the hottest year on record, according to a report this month in the Washington Post. “The past 18 months have shattered global temperature records,” adds Ed Hawkins, a climate researcher at the University of Reading in the UK. “The dominant cause is the long-term increase in temperatures due to human activities but global temperatures in individual years and months also fluctuate due to weather patterns and factors such as El Niño.”
Arctic Oscillation & Polar Vortex 3.0 - Major Players
Our area is expected to be cold and snowy this winter. For that reason, it seems important to make the point that a wintery winter does not negate the reality of climate change.
In writing about a similar prediction for 2011-12, Dr. Rood said, “Of course, those whose opinions on global warming are anchored in the political arguments use the cold and snowy winter to substantiate their position that global warming is not real...Others become sensitized to the weather and start to think about climate and changing climate and what such a cold and snowy winter means.”
Increasing Carbon Dioxide Levels: Melting Arctic Ice and Changing Arctic Oscillation Patterns
Dr. Rood explained that the Arctic Oscillation is often more important to Michigan than El Nino. “The way carbon dioxide changes the Earth’s climate is by changing the heating and cooling. A common comparison is to compare additional carbon dioxide to a blanket which holds the Sun’s heat closer to the Earth’s surface. This blanket causes the Earth to heat up more at the pole than at the Equator. The poles are also special because the Sun goes down for the winter and it cools off. In fact, it gets very cold, and as discussed in the previous blogs, the stream of air that gets spun up isolates the pole enough to let the cooling really get going. With these changes to heating and cooling, if we add a lot of carbon dioxide to the atmosphere, then it is reasonable to expect that the Arctic Oscillation might change.”
Videos About These Topics From Dr. Rood: