Warm air is spiraling into the developing storm from the southeast, swirling in the all the way from the Gulf of Mexico. This air will ride up over the chilly air on the backside of the storm, climbing high into the sky in a region called the “comma head.” This is where heavy snow wraps in on the west side of the storm — the overlap of cold air, moist flow at the mid-levels, and dynamic lift in the atmosphere.
The combination of these three features will lead to prolific snowfall rates from northern New Jersey and New York City, to western Connecticut and central Massachusetts. Anyone along Interstate 95 in the Northeast away from the immediate coastline is in play for a four-hour period of two to three inches per hour snowfall rates.
What is so exciting about this storm to meteorologists is the type of atmospheric instability that will lead to this potential thundersnow.
Ordinary thunderstorms develop vertically as less dense air near the surface rises. That scenario is tough to get in the wintertime; instead, thundersnow typically develops in quickly spinning nor’easters when pockets of air are forced diagonally upward into the atmosphere.
Wednesday’s scenario is unique because the air at the mid-levels is so incredibly cold. That will enable the generation of “traditional” vertical instability, just like in the summertime. The result could be a spectacular — and unusual — light show in major metropolitan areas of the Northeast during the height of the storm. The National Weather Service Storm Prediction Center has included many Northeast cities in their thunderstorm outlook, a highly atypical move in the wintertime.
Even weirder is that individual thundersnow cells could even produce some small hail. Yep, that’s right — snow, thunder and hail all at the same time. With air climbing high into the sky so rapidly, it’s not out of the question that it gets to the level at which hailstones form. Tiny pellets of ice, called graupel, may shower down during intense burst of snow, but a few hailstones of pea or even dime size could occur in the most intense thundersnow.
Thundersnow is rare to begin with, and the muffling effect of snow makes it tough to hear even if it occurs. Most of the time, it appears just as a blue flash — blue because of the high concentration of ice crystals in the air.
If you happen to catch the roar of thunder, you’re probably within a mile or two of the strike. Even though it may seem harmless, don’t be fooled — thundersnow is just as dangerous as a summertime thunderstorm.
During a blizzard last year on Feb. 9, a bolt of lightning blasted a hole through a family’s house in Cranston, R.I., while a nearby strike ignited a house fire in Providence. It’s good to put off shoveling until after the lightning threat has diminished. Just as you wouldn’t go golfing and hold an nine-iron on the seventh fairway during a summertime storm, it’s not smart to be holding a metal shovel up during thundersnow.
There is an increased likelihood of thundersnow being observed in the vicinity of high towers and city skyscrapers. The pointed tips of these structures can literally poke into the cloud base and concentrate otherwise low ambient electric fields, building a charge that eventually triggers a lightning strike. Folks in New York and Boston especially should keep an eye out for this; in Hartford, the tallest buildings are about 400 feet too short to spark a flash.
The storm will pull away late Wednesday into Thursday morning as it departs into the Canadian Maritimes. But if you happen to hear some rumbling during the storm, don’t be “shocked.”