Beyond the Vortex: A Winter Wonderland of Cause & Effect

Snow storm warning, weather, polar vortex, jet stream, weather extremes — (Image credit: Olaf Naami | Shutterstock.com)

Matt Kelsch is a hydrometeorologist with COMET, a division of the University Corporation for Atmospheric Research (UCAR). Kelsch contributed this article to Live Science's Expert Voices: Op-Ed & Insights.

A fast-moving but potent nor'easter is bringing rain, snow and wind to the urban corridor from Virginia to Maine on Thanksgiving Eve, one of the busiest travel days of the year. The storm is taking advantage of the still-warm ocean and the cold air mass over the central United States, and there is travel-snarling heavy snow in, or just inland, from the major coastal cities.

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Even snow-savvy Buffalo, N.Y., met its match when "lake effect" snow squalls formed as cold arctic air swept along the length of Lake Erie converting the relatively warm, moist lake air into narrow bands of intense snow. The result was locally paralyzing snowfall to depths up to 5 feet (1.5 meters) within a 24 hour period, and storm totals greater than 7 feet (2.1 meters), perhaps making it the most intense such storm associated with Lake Erie. This time-lapse shows the snow-laden clouds moving eastward from Lake Erie into the hard-hit southern suburbs of Buffalo.

So what do the terms mean? Let's start with the simple reminder that the jet stream forms in the upper atmosphere between the cold polar regions and the warm tropics. The jet stream encircles the Earth at somewhere between 4.5 miles to 7.5 miles (7.2 kilometers to 12 kilometers) above sea level, flowing rapidly from west to east, with the warm air on the equator side and the cold, denser air — the polar vortex — on the poleward side.

If the Earth's surface were featureless, the jet stream would likely follow a nearly perfect circle around the world, and the cold air would stay in polar regions. But the Earth's varied land forms and vast oceans, with their warm and cold currents, cause big differences in how the planet's surface warms. As a result, the jet stream departs from its west-to-east flow and zig zags in places, allowing tropical air to penetrate into polar regions while arctic air surges down into mid-and low-latitude areas.

That disruption to the west-east oriented jet stream resulted in a southward kink of that river of air ,which pushed record cold into middle latitude areas of the mainland United States. Following the cold wave, the "wavy" jet stream led to a quick warm-up in the central and eastern United States followed by another cold surge in time for Thanksgiving Eve while much of the West should see mild Thanksgiving weather.

So many are wondering if this pattern is an indication of the winters to come. Some indications in the arctic suggest it may be, such as an above-average amount of early-season snow cover in Siberia, which may be correlated with cold winters in the central and eastern United States. But there is also growing evidence that a weak to moderate El Nino is emerging in the tropical Pacific, and El Nino winters are usually — but not always — associated with reduced risk of frequent arctic outbreaks (frequent multi-day spells of very cold air that originated in the frozen tundra of the arctic region) and potentially more rain for drought-stricken southern California.

The winter forecasts for 2014-2015 in the United States vary across the different projections from government agencies and private enterprise. The large snow cover in Siberia has prompted some to call for a winter with more cold-wave action than usual. Yet the increasing indications from El Nino have some, such as NOAA, calling for a lowered chance for frequent spells of arctic cold. The data that the different agencies analyze is pretty much the same, but the weight assigned to each of the many driving forces differs.