For the tens of millions who live in the Midwest, Mississippi River Valley, Ohio Valley, and the East Coast, the first taste of true winter weather is just days away. Ushered in by a powerful cold front, the cold air, with high temperatures running 10 to 15 degrees below average, will come as a shock following one of the warmest fall seasons on record.
Computer models are in agreement that the weather pattern across the Northern Hemisphere will become extremely amplified, which means that the jet stream -- that high altitude superhighway of winds that steers weather systems and forms the boundaries between air masses -- will carve out large dips, or troughs, as well as strong, practically immovable "blocking" ridges.
Such weather patterns are ideal for creating extreme weather.
SEE ALSO:La Niña is officially here to shape U.S. winter weather, along with global climateThis configuration of the jet stream will lead to a bizarre but increasingly common situation in which the Arctic is unusually mild for this time of year (while still being cold, by lower latitude standards), as parts of North America, Europe, and Asia experience colder than average conditions.
Via GiphyHowever, there are two big caveats to keep in mind about the cold air about to invade the East Coast, so don't panic quite yet.
First, the cold air coming to the U.S. won't be coming straight out of the Arctic, but rather it will be oozing south from Alaska and Canada. It also won't traverse snow-covered ground, keeping the cold air warmer than it might otherwise be.
Snow cover across the lower 48 states is unusually low, with virtually no snow on the ground south of the U.S. border with Canada from Michigan eastward.
All that means that this will not be a historic cold snap, not even close. One should expect few, if any, cold temperature records to be set or tied during the coming two weeks, even though temperatures will run below average in the eastern half of the lower 48 states.
Computer model projection showing a cold air mass in place across the Midwest and eastern U.S. as of Dec. 9, 2017.Credit: weatherbell analyticsSecond, while the large-scale weather pattern will be primed for a big East Coast snowstorm, with a blocking high pressure area over Greenland, a negative phase of a cycle known as the Arctic Oscillation, and a deep dip in the jet stream from Canada southward to the Gulf of Mexico, it's unclear if any formidable storm will materialize.
Winter storms require a spark or trigger in the form of atmospheric energy riding along the jet stream. As of Monday, computer model projections showed no indications of a significant storm in the near-term, 7-day period.
We'll have to wait and see if one emerges after that.
Tweet may have been deleted
For East Coast snow lovers, it would be a huge disappointment if the next 14 days or more turn out to be cold and dry, despite most of the pieces being in place for a big storm.
There is one snow-making machine that will kick into gear with the arrival of the cold front: lake effect snow.
As cold air blows across relatively mild, unfrozen waters, moisture will be dumped downwind in the form of heavy snow squalls. Feet of snow could pile up in parts of Michigan, Wisconsin, Illinois, Ohio, and New York State.
This will at least increase the proportion of the U.S. with snow cover, which stood at a measly 15.5 percent as of Monday.
Featured Video For You
A giant sculpture translates vibrations of 40,000 live bees into an explosion of light and sound
何禹萱
狼啸
黄新德
