To a significant part of the East Coast, it can be a matter of 100 or 200 miles in the course of a storm whether the falling snow is scenic or disruptive. The reason why that thin margin is generating the recent uncertainty in the forecast of a fast-strengthening winter system that will develop off the Carolinas, and with enough intensification potential to reach the level known as bombogenesis by the meteorologists.
Guidance is all the same: a coastal low will develop in the vicinity of the Carolinas at the beginning of the day on Saturday, and then it will become quite strong as it proceeds towards the northeast. The term bomb cyclone is not used to characterize a different type of storm itself, but rather to characterize speed, the pressure that falls rapidly enough to accelerate the winds, narrow the difference between high and low pressure, and put a lot of precipitation in a very small area. In the given scenario, the air has already been already charged with cold air, and the chances of sloppy mix are decreased, and the chances of cleaner snow where the moisture of the storm mixes with the subfreezing temperature increase.
The most predictable one is to the south of the mid-Atlantic: North Carolina and south-central Virginia are within the sphere of greatest confidence regarding substantial snowfall and strong gusts. To the north of that, the confidence level falls very fast due to the fact that small variations in track mean that the snow shield of the storm will be on one group and the wind and cold on the other with little to no accumulation.
This is why forecasters have several scenarios on play. In the front track, the low remains very close to the shore as it intensifies. The Carolinas, southern Virginia and some northern coastlines are targeted by snow and wind, and most cities along the Interstate 95 corridor, such as Washington, Baltimore, Philadelphia and New York evade the worst bands. Onshore wind combined with low pressure still has a role to play even in that outcome that was mostly spared: the high water and the strong winds will push waves into exposed coastlines between the Outer Banks and southern New England.
An approach closer to the shore vastly extends the area of influence. Should the storm follow the coast as it intensifies, increasing snow and greater intensity spread northwards into the population centres of the mid-Atlantic and the Northeast. Such also increases the likelihood of coastal inundation and beach erosion due to the closer proximity of the strongest wind field to the land over a longer period of time, which causes water to be directed at inlets and bays, and enhancing the surges along the shore.
A third, less-probable scenario lies on the table which is formed further out in the ocean and moves into the sea leaving its strongest winds and heaviest liquid in the Atlantic. At that, the effects would decreased sharply even in those areas bracing in the Carolinas.
This system is different than the previous large storm in one aspect: scale and texture. Rather than a wide band of mixed precipitation moving far inland, this arrangement acts like a typical nor’easter, small, ocean-based, and free to focus the dangers along the coastal plain. Once a storm intensifies rapidly, the potential ingredients of blizzard conditions may intersect without unprecedented amounts of snowfall: high-speed winds, falling or blowable snow, and poor visibility.
Formally, the National Weather Service considers a blizzard to be wind more than 35 mph with a visibility less than a quarter mile during at least three hours. This particular fact is important to those households that need to make choices on what to be taken seriously: blowing snow will result in a minute amount of accumulation becoming dangerous traveling conditions, particularly when cold air is already established and drifting piles grow rapidly.
To the Carolinas folk and the New England folk, the label need not be taken since the lever is track. Models move towards convergence, and the prediction usually narrows down to place-specific, who is under the snow axis, who is in windy fronts and who has a cold, breezy weekend instead.
