File:Cloud streets off the northeastern United States (MODIS 2018-01-01).jpg

English: As 2017 drew toward a close, Arctic air spilled into the eastern United States and Canada for several days. Blasts of bitterly cold air set up a white Christmas for many Americans, and forecasters are expecting New Year’s Eve celebrations to be the coldest in recent memory for many areas.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this true-color image of the frozen Northeast landscape on December 28, 2017. Brisk northwesterly winds created rows of “cloud streets” as cold air blew over Lake Ontario and the Atlantic Ocean. A layer of snow covered much of New England and upstate New York.

Cloud streets are long parallel bands of cumulus clouds that form when cold air blows over warmer waters and a warmer air layer (temperature inversion) rests over the top of both. The comparatively warm water gives up heat and moisture to the cold air above, and columns of heated air called thermals naturally rise through the atmosphere. The temperature inversion acts like a lid. When the rising thermals hit it, they roll over and loop back on themselves, creating parallel cylinders of rotating air. As this happens, the moisture cools and condenses into flat-bottomed, fluffy-topped cumulus clouds that line up parallel to the direction of the prevailing winds.

While the cold streak has not broken all-time records, it is breaking records for individual days. On the day the image was acquired, weather observers on Mount Washington (New Hampshire) recorded a daily record low of -34 degrees Fahrenheit (-36° Celsius). Baltimore, Boston, Flint, New York, Montreal, and Toronto Cities have seen records fall during this cold snap.

For the ball drops in New York City on New Year’s Eve, forecasters expected air temperatures of 10°F (-12°C), with wind chills of -5°F ( -15°C). The last time it was so cold was in 1962; the record for the coldest ball drop occurred in 1917, when the air temperature was just 1°F (-17°C), according to Jason Samenow of the Capital Weather Gang.

The cold weather pattern has its origins in a large bulge, or ridge, in the jet stream that has brought unseasonably warm weather to Alaska. On the east side of this ridge, a trough in the jet stream plunged southward, bringing plenty of Arctic air with it. This orientation of the jet stream, which looks similar to the greek letter omega, is known as an omega block.