In recent decades, the Northern Hemisphere has featured a “Warm Arctic, Cold Continents” (WACC) pattern, combining the warming and rapid sea ice loss of the Arctic with the frequent occurrence of cold, harsh winters over Eurasia and central North America.
A new study, funded in part by CPO’s Climate Variability and Predictability (CVP) program, investigates the drivers of interannual, or year-to-year, variability in the WACC. The research, published in the Journal of Climate, focuses on the WACC pattern over the North American region, as opposed to the Eurasian content, which has been the focus of most WACC studies. Determining which key processes are responsible for the formation of and variations in the WACC pattern is complex and challenging.
Previous research shows that sea ice loss, warming Arctic surface air temperature, and tropical sea surface temperatures may all play a role, along with the WACC’s own internal atmospheric processes. This study quantitatively characterizes the relative importance of the different key drivers of the WACC interannual variability over the North American region using both observations and multi-model simulations.
This study finds that internal atmospheric variability plays an important role in determining the variability of the internannual WACC pattern. Furthermore, unlike the WACC over Eurasia, the North American pattern seems to be more responsive to changes in sea surface temperature than Arctic sea ice. This link between sea surface temperature and WACC variability could serve as a useful predictor for seasonal climate predictions over the North American region.
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After 2 years of snowless winters, the upper midwest has seen an extended period without a thaw, leading to the thickest snow some areas have seen in years, including where I’m at.
Some areas in the Great Lakes are seeing record snowfall this winter, thanks in part to global warming–or “global weirding,” as I prefer to call it!
That’s because hasn’t been cold enough for most lake areas, other than Lake Erie and Georgian Bay, to completely ice over yet. So as cold air masses sweep across warmer lakes, they’re picking up more moisture. And this means greater snowfalls on the windward (typically south and east) sides of the lakes.
As you can see from the images here, most of the Great Lakes area is still open as of this week; and lake ice, while not record-setting, is below average. As a result, this season has already seen some impressive lake-effect snow and there is certainly more to come.
Historically speaking, Great Lakes ice cover is highly variable from year to year. However, since 1995 there have been 8 years at or below 20% coverage. And that’s why, although snowfall has been decreasing in more southern locations, lake effect snow hot-spots in the Great Lakes region are growing as the planet warms.
Rutgers University Snow lab has snow fall graphs for the Northern Hemisphere that are instructive. If you look at the Northern Hem Winter snow extent, you can see how a climate denier would use this as “proof” that the climate is even cooling.
Of course, this is completely consistent with Hayhoe’s explanation above, more moisture in the atmosphere. Ask any ski resort operator in the midwest, and they’ll tell you, sure, it snows, but in most years we consistently get strong thaws that greatly impact snow thickness and quality. This year is the first in a long time we have not had a pattern of thawing.
Where the warming shows up is in Spring snow extent.
