© tropicaltidbitsModel projection of the satellite signature of the major storm, from the NAM model.
An unusually powerful storm is threatening the East Coast of the U.S. this week with heavy snow, high winds, and record-shattering cold not seen in some places since the early 20th Century - if at all.
The storm will be the result of a combination of three strong pieces of atmospheric energy, known to meteorologists as shortwaves.
Think of these shortwaves as protein bars for storm formation. This particular storm, which is already beginning to form off the coast of Florida, will devour enough of them to allow it to become so powerful that it will contain hurricane force winds by the time it moves off the Mid-Atlantic coast late Wednesday night.
Because of the cold air in place ahead of the storm, winter storm watches and advisories for this event have been issued as far south as Florida, all the way northward to Massachusetts, which is nearly unheard of.
In fact, some computer model runs show that the storm could intensify far faster than what would be required for the tempest to be known as a weather 'bomb,' for a process called "bombogenesis."
This term refers to a low pressure area whose minimum central air pressure plummets by at least 24 millibars in 24 hours. By feasting off of intense atmospheric disturbances as well as differences in air masses and ocean temperatures, including the moisture rich Gulf Stream waters, the upcoming tempest is projected to exceed that intensification rate by several more millibars in 24 hours. This intensification rate, if it comes to pass, would be astonishing.
A minimum central air pressure of below 950 millibars would be an unprecedented intensity for a non-tropical storm in the Northeast during the past 30 years, according to Anthony Sagliani, a meteorologist at Earth Networks.
Some computer models are projecting a minimum central air pressure of below 950 millibars at its peak, which would be nearly unheard of for this part of the world outside of a hurricane. For comparison, Hurricane Sandy had a minimum central pressure of about 946 millibars when it made its left hook into New Jersey in 2012.
In general, the lower the air pressure, the stronger the storm. Computer model projections show that this storm is likely to reach a peak intensity that is rarely seen off the East Coast, with a minimum central air pressure of about 950 millibars. This is comparable to the air pressure measured in a Category 3 hurricane.
Storm track is key
The big question concerns the storm's track. As of Tuesday at midday, most computer model projections and human-made forecasts showed it heading just close enough to the Mid-Atlantic and New England, as well as the Canadian Maritimes, to bring significant impacts in the form of high winds, heavy snow, and possible coastal flooding.
Computer model runs on Tuesday showed a growing risk of blizzard conditions in Southern New England on Thursday, due to the combination of heavy snow and strong winds. Even parts of Delaware, Maryland, and Virginia could see close to blizzard conditions for a time as well.
An animation of projected satellite imagery, showing the explosive storm development along the East Coast. This is NAM 3KM model data.
New York City is straddling the line between a heavy snowstorm and a moderate event. It would take another 50-mile shift westward in the storm track, which is entirely plausible at this point in the game, to put New York City in the crosshairs for heavy snow as well, and a 100-mile shift - which is also within the realm of possibility, would put inland areas in play, too. The forecast trend through midday Tuesday has been to move the track slightly to the west, giving forecasters in New York, Philadelphia, and Connecticut heartburn.
A track wobble further offshore, of course, would lessen the anticipated coastal impacts along the East Coast.
As of Tuesday morning, the National Weather Service was forecasting 2 to 4 inches of snow in New York City from this storm on Wednesday night through Thursday, but such amounts may have to be raised given the storm track shift to the west.
The track of the storm depends on the subtle interactions between the two pieces of energy diving southeastward from the Pacific Northwest, as well as energy from the southern branch of the jet stream. Even with supercomputers and other modern assets at their disposal, forecasting storms such as this one still tests meteorologists' ability to anticipate what the capricious atmosphere will do.
Nova Scotia is likely to take a direct hit from this storm on Friday, with widespread power outages from hurricane force winds, along with heavy snow, heavy rain, and battering waves. This could be a storm for the record books there, as well as Downeast Maine, again depending on the exact track of the low pressure area.
Stupid-level cold follows this storm
Even if the storm leaves a fluffy 3 to 4 inches of snow in New York and Philadelphia, rather than a crippling blizzard with snow measured in feet, it is still going to have one dangerous impact that is quite certain to occur in those locations. The heart of cold air over North America and parts of the Arctic is currently parked over Hudson Bay, Canada.
© weatherbellTemperature departures from average projection from the Euro model for Saturday morning, Jan. 6, 2018.
How rude.
The cold weather that will result is going to be more frigid than anything that residents of the Midwest and East Coast have experienced so far during what has been an unusually intense and long-lasting cold snap. Instead of breaking daily temperature records, as dozens of cities have been, all-time cold temperature records will be threatened on Friday, Saturday, and Sunday.
For example, the high temperature in New York City may not get above the single digits on Saturday, with overnight lows in the metro area plunging below zero.
© nws/weatherbellForecast record cold high temperatures on Friday, Jan. 5, 2018. Broken records indicated by circles.
As former Weather Service meteorologist Gary Szatkowski explained via Twitter on Tuesday morning, areas that don't get much snow from this storm, but that do get into the heart of the cold air mass, could have more infrastructure problems since snow cover acts as an effective insulator to the ground below it.
For people venturing out into the cold this weekend, frostbite will be a risk on any exposed skin within minutes of being outside, particularly on Friday night, as gusty winds whip across the Northeast behind the storm.
The good news, however, is that there are signs of a "warm up" toward more average temperatures in the Midwest and East by early to midweek next week.
Hang in there, folks.
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