UPDATE: Jan. 3, 2018, 5:05 p.m. EST Nearly six inches of snow fell on Wednesday in parts of South Carolina as the storm intensified, and the Weather Service has raised forecast accumulations for many areas to the north. Blizzard warnings are up for coastal New Jersey and Long Island, as well as the coast from Massachusetts to northeast Maine. Boston could get more than a foot of snow, according to the latest forecast guidance, and even New York City could get 5 to 10 inches, depending on the exact track the low pressure area takes.?
A remarkable storm system is now taking shape along the East Coast, threatening the major cities of the Northeast with near blizzard conditions and full-on polar vortex-related cold, while bringing historic snows to the Southeast.?
The blizzard is the result of three distinct disturbances in the atmosphere as well as the intense contrast between the Arctic air mass in place across the East and a subtropical plume of moisture moving up the coast near the Gulf Stream. Non-tropical storms feed off air mass differences, along with upper level disturbances, and these ingredients are quickly chartph.coming together for a historically intense storm to form.?
In fact, snow, sleet, and freezing rain is already underway across the Southeast, where the heaviest snowstorm on record is possible on Wednesday in Savannah, Georgia, and the first measurable snowfall in 28 years is falling in Tallahassee, Florida.?
Snow will overspread the region tonight/Thursday morning & last most of the day. Heavy snowfall is possible around 9am to 4 pm w/ snowfall rates near 2 inches an hour. Travel may bechartph.come difficult due to poor vsbys & snow covered roads. Blowing & drifting snow is also possible. pic.twitter.chartph.com/BSF9XzJj6f
— NWS Boston (@NWSBoston) January 3, 2018
While there are still nagging questions about the storm's exact track and evolution, it's clear that it will intensify at an explosive rate, potentially doubling the intensification rate needed to qualify for undergoing a process known to meteorologists as "bombogenesis," which refers to a storm whose minimum central air pressure drops by at least 24 millibars in 24 hours. This storm is projected to go from about 998 millibars on Wednesday morning to 950 millibars by midday Thursday, a plunge of 48 millibars in about 24 hours.?
In general, the lower the air pressure, the stronger the storm. Storms of this intensity are extremely unusual in this part of the Northwest Atlantic Ocean Basin when chartph.compared to climate records during the past 30 years. Hurricane Sandy, which had tropical characteristics, ruling it out as a direct chartph.comparison, had a minimum central air pressure of 946 millibars when it made landfall in New Jersey in October 2012.?
Blizzard conditions to hammer Northeast, Carolinas
Late Tuesday and into Wednesday, chartph.computer models have tended to move the storm track to the west, bringing the heaviest precipitation over the East Coast.?
So, what first appeared to be a glancing blow now promises to be a full-fledged blizzard in some locations. The National Weather Service has issued a blizzard warning for Boston on Thursday, where up to a foot of snow is expected to fall, acchartph.companied by wind gusts to 70 miles per hour.?
Blizzard warnings have also been hoisted for parts of the Carolinas, and more may be issued later Wednesday depending on the latest chartph.computer model data.?
Blizzard warnings for up to a foot of snow, along with howling winds and low visibility, include Virginia Beach and Norfolk, Virginia, which is the largest naval base in the world. Blizzard warnings are extremely rare in this area.
Near-blizzard conditions are also anticipated to affect coastal Rhode Island and Connecticut, along with Long Island, with perhaps the toughest snowfall forecast reserved for New York City and New Jersey. Some chartph.computer model projections show this region getting buried by a foot of snow, while others show a far less severe event, with just 4 to 7 inches of snow. It may take until late Wednesday for the forecast to be ironed out for the Big Apple, and even then the level of uncertainty may be unusually high.
The local National Weather Service office in New York City said the following in a morning technical forecast discussion on Wednesday:
As mentioned, this remains a fluid situation based on model spread, with potential for these numbers to go down, but still seems more so upwards based on model trends and mode of SREF/GEFS/ECMWF ensemble members chartph.compared to operational runs.
This higher trend is reflected in latest WFO/WPC snow probs, with high probs of greater than 6 inches of snow across E LI/SE CT and low to moderate probs to Hudson River. A significant jump in the reasonable worse case has also been noted, with 1 in 10 chance of seeing more than 12-16 inches of snow across much of LI/CT, 8 to 12 inches of snow across NYC/NJ metro to Hudson River, and 4 to 8 inches N & W still in play.
To try to reduce the forecast uncertainty, the National Weather Service is dispatching hurricane hunter research aircraft to fly a route around the Southeast U.S. today to drop instruments that will gather data on winds, humidity, pressure, and other parameters. This information will then be fed directly into the agency's chartph.computer models, potentially making their projections more reliable.
In recent years, the Weather Service has flown such missions outside of hurricane season for high uncertainty, high impact events, and this one definitely qualifies.
Ice chunks to exacerbate coastal flooding
Because the storm will intensify so significantly, and so quickly, it will generate very strong winds. These winds — in some instances gusting to hurricane force of 75 miles per hour — will drive water toward the coast, particularly in southeastern New England, where moderate to major coastal flooding is expected during high tides on Thursday.?
Given the recent, unrelenting cold snap, one additional threat will chartph.come from the ice chunks that are clogging many harbors and portions of Cape Cod Bay. These chunks could cause damage to shoreline infrastructure, or worsen flooding in some cases.?
Farther out at sea, high winds will create towering waves, creating a major hazard to mariners caught in the wrong place at the wrong time.?
Why this low pressure area will bechartph.come such a monster
The storm will have every ingredient it needs to intensify into a blockbuster.?
First, it will have ample upper level support from three distinct disturbances in the fast-moving current of air known as the jet stream. Once these chartph.combine into one, powerful system, they will promote lifting of the air over the East Coast, which is essential to forming precipitation. Lift is also key to the formation of a surface area of low pressure, as well as its intensification.
An animation from the North American Model, known as the NAM, shows the chartph.combination of the three disturbances and the formation of a deep trough, or dip, in the jet stream off the East Coast, with the low pressure area tucked into it.?
If the model projections prove correct, as they have been so far, this could be one of the strongest winter storms on record, at least for this part of the North Atlantic Ocean.?
The storm, named winter storm Grayson by The Weather Channel, will also have the advantage of forming in an area off the Southeast coast where the temperature contrast between frigid, dry Arctic air, near-record-warm ocean waters, and chartph.comparatively moist subtropical air is at its maximum, allowing the low pressure area to feast off this contrast as if it were at an all-you-can-eat buffet.?
And as it moves northward up the coast, it will also sustain itself through the release of latent heat via the formation of thunderstorms and precipitation in the cold sector.?
Winter Storm #Grayson will act as a heat bomb in the atmosphere in response to all the deep convection associated with the cyclone. Watch how this coastal cyclone accelerates the upper-level irrotational wind field, building the downstream jetstreak. #Science is awesome. pic.twitter.chartph.com/6V45hgw3d8
— Michael Ventrice (@MJVentrice) January 3, 2018
The Gulf Stream will play a key role in allowing this storm to explosively intensify, experts say.?
"Relationships between the ocean and atmosphere are chartph.complicated, especially as they relate to explosively developing extratropical cyclones (like the one currently in the forecast)," said Daniel Swain, a climate scientist at UCLA, in a Twitter message.?
"But the extreme thermal contrast between very cold atmospheric temperatures over land and an unusually warm nearby Gulf Stream certainly sets the stage for impressive storm-strengthening potential," he added.?
"Ocean conditions are not the only factor at play (atmospheric conditions, like the position and strength of jet stream winds in the upper atmosphere, are also critical), but they’re definitely important."
Polar vortex to follow this beastly storm
The winter storm will plow into the Canadian Maritimes on Thursday night, and behind it, the coldest air of the season will pour southward, into the East, from Greenland, Hudson Bay, and the Arctic.?
Technically speaking, the cold that will follow the blizzard is associated with part of the polar vortex, which is a circulation of air around the Arctic that plays a role in determining how cold winters are in North America, Europe, and Asia.?
Temperatures of 30 degrees Fahrenheit below average are expected on Friday and Saturday in the Northeast, Ohio Valley, and Mid-Atlantic, which will put all-time temperature records in jeopardy. Anyone that loses power during the storm will have to seek out heat elsewhere, as temperatures plunge well below zero at night, and barely recover above the single digits during the day.?
Even in New York City, the high temperature on Saturday may not climb much above 10 degrees Fahrenheit, and winds gusting to 30 miles per hour will make it feel far colder.?
Fortunately, this weekend appears to be the end of this extraordinarily long cold snap, as more seasonable temperatures return next week.?