A major winter storm is getting its act together over the south this evening, threatening most of the southeast from Arkansas to Virginia with heavy snow and freezing rain on Monday and Tuesday. Little Rock and Memphis could see an ice storm, while snow accumulations of more than one foot are possible to the east.

The Setup

A budding area of low pressure over northeastern Texas will quickly get its act together as upper-level winds grow more favorable for development through the evening and nighttime hours on Sunday. The enhanced lift at the surface, along with an influx of moisture from the Gulf of Mexico, will allow a cold and juicy storm to produce heavy snow and ice along a large stretch of real estate from the Mississippi River to the Atlantic Ocean that doesn't typically see that much winter weather, let along a significant storm on this scale.

Once the storm moves off the coast of North Carolina on Tuesday morning, it will hook northeast and bring some light/moderate snowfall to the I-95 corridor from Washington D.C. to Boston. Snowfall totals across the megalopolis will range from five or more inches towards D.C. and Philly, to just a few inches closer to New York and Boston.

Snow Accumulations

Let's jump right into snowfall totals. It doesn't take much snow to break records around here, and for good reason: it just doesn't snow very often. Storms need to take a specific path out of Texas or away from the Gulf Coast in order to produce heavy snow across the mid-south, and even then, it's pretty hard for cold air to overpower warm air in the right sequence to produce snow. The latter point will contribute to major freezing rain and sleet mixing with snow towards the southern edge of the system, but we'll get into that in a moment.

The heaviest snow will fall over Tennessee and Kentucky, with the National Weather Service currently predicting more than a foot of snow in eastern Kentucky. This could break some all-time snowfall records. The largest snowfall ever recorded at the airport in London, Kentucky (KLOZ), was 15.0 inches on March 9, 1960. The city's current NWS forecast shows the potential for 14.6 inches of snow, which would come in second and rival the all-time snowfall record.

Elsewhere, a widespread snowfall of four to eight inches is likely from western Missouri through Virginia and probably the Delmarva Peninsula. The National Weather Service's Enhanced Data Display only shows snowfall accumulations through 7 PM on Tuesday, so it doesn't fully cover the eastern extent of the storm yet. Contrary to the above map, for example, the Washington D.C. area could see five or more inches of snow as the system passes to the east.

The Weather Channel, which produces pretty good forecasts (despite their silly naming scheme), expects higher snowfall totals than the National Weather Service. The Atlanta-based weather behemoth expects a swath of 12 to 18 inches of snow stretching from western Kentucky through the mountains of Virginia, with a larger 8- to 12-inch region from Missouri to the Atlantic Ocean.

Some areas towards the southern extent of the snowfall will experience mixing as a result of mid-level warm air intrusion, even if temperatures at the surface are well below freezing. Any sleet or freezing rain that mixes with the snow will hold accumulations down, but it will leave the snow more watery and compact, making it heavier, harder to shovel/plow, and potentially freeze it solid once temperatures drop to near-record levels once again on Tuesday night.

Winter storms in the south are typically on the lighter side—last year, for instance, we saw just a couple of inches of snow in Birmingham and Atlanta, and that was just enough to cripple the area for several days. As Gizmodo's former Editor-in-Chief Brian Barrett pointed out at the time, we are just not equipped to deal with snow in the south. Places like Tennessee and Kentucky are more equipped than Alabama and Georgia, but snow and ice has a much different mental and physical impact than it does in places up north that are used to wintry weather.

Ice Accretion

Meteorologists generally agree that the worst freezing rain will occur across parts of central Arkansas, southern Tennessee, and northern Mississippi, though they differ on who will see the most ice. The National Weather Service (above) calls for significant ice accretions on the order of at least one-quarter of an inch from central Arkansas through the Memphis metro area. Parts of the Tennessee mountains (around Knoxville) and the Greenville-Charlotte corridor in the Carolinas could also see accretions of one-quarter of an inch or more.

Ignoring the silly name plastered on the map above, The Weather Channel (whose winter storm names are purely advertising) slightly differs with the NWS on the location/amount of ice, but they agree that the I-40 corridor between Little Rock and Memphis will see a major ice storm overnight on Sunday and into Monday.

The center of this storm will serve as a boundary between relatively "warm" air to the south and the very cold Arctic air to the north. In many locations just north of the track of the low, temperatures at the surface will remain below freezing, while above-freezing temperatures flow in from the south just a few thousand feet above ground level. Just imagine a wedge of warm air sitting around 3,000 to 4,000 feet above the ground.

This invasion of warmer air at the mid-levels will cause snowflakes to completely melt as they fall through the above-freezing temperatures. These newly-formed raindrops will fall into the sub-freezing air near the surface and become supercooled; that is, the raindrop's temperature will dip below freezing, yet the droplet will remain in liquid state as it has no impurities around which to refreeze. The supercooled raindrops will freeze on contact once they land on any exposed surface outdoors, completing a much-hated process we know as "freezing rain."

The longer the cold air remains at the surface with warm air aloft, the longer we'll see freezing rain.

Any glaze of ice on sidewalks, porches, steps, decks, and roadways is dangerous for pedestrians and drivers. It's possible to gain some traction in snow, but ice is unforgiving and favors no one. Once ice accretions reach that "significant" level of one-quarter of an inch, it sufficiently weighs down tree branches to where some may snap, and the weight (which can equal hundreds of pounds) can start to bring down power lines. Greater ice accretions equal greater weight, which equates to more tree and power line damage.

Impacts/Travel Hazards

Power Outages: Folks who live in areas that see freezing rain are at an increased risk of seeing power outages as a result of trees and power lines coming down under the weight of the ice. People losing control of their cars and crashing into power poles is also a factor. This storm shouldn't have the severe winds that we saw with the one that just hit New England, but any wind with the weight of snow and ice can stress trees and lines to their breaking point. Make sure you're prepared for an extended power outage, keeping in mind that you'll need cash, gas, medication, water, food, and a fully-charged cell phone.

One of the biggest risks with power outages includes people using fire (candles and fireplaces) for warmth or light; it's pretty easy to forget about a candle or knock one over. Never use a grill or gas-powered generator indoors unless you really want to die of carbon monoxide poisoning.

Tree Damage: If you're out and about on foot or by car, watch the trees above you and steer clear of any branches or limbs that look like they're on the brink of snapping. Listen for cracking sounds (it's very audible with ice present) and go the other way if you feel you're at risk. If you live in a home surrounded by trees, try to limit the time you spend on a side of the house susceptible to damage if a tree were to fall into your home.

Schools: Closed. It doesn't matter if you're going to see a dusting or a foot. Schools will be closed for at least a day, if not longer.

Flights: Cancellations are highly likely at smaller airports across the south. Charlotte is the largest hub affected by the storm, and will likely experience major delays and cancellations as a result of the snow and ice in the Queen City. Atlanta should escape the wintry weather by the skin of its teeth, but heavy rain and wind will likely cause congestion delays. Washington D.C. and Philadelphia are on track if current forecasts hold up, so many flights to and from those hubs will also see major delays or cancellations.

Car: Municipalities that haven't fully funded/prepared for road sanding and snow removal will have a hell of a time keeping up with the snow and ice from this system. Stay home if you can. We don't want another commutageddon like we saw last year.

Foot: It will be nearly impossible to walk in areas that see freezing rain. Stay indoors unless your house is on fire. If you absolutely must walk outside when it's icy, sprinkle rock salt, sand, or kitty litter in front of you as you walk. Walk with a flat foot to maximize surface area and evenly distribute your weight. Walking on the grass is usually a good bet (especially if there's a coating of sleet or snow present), but once ice accretions reach one-tenth to one-quarter of an inch, even grassy surfaces will become a skating rink.

Train: As a general rule, passenger trains do not run when there's ice on the tracks, and it's unlikely that any train service will occur in areas that see wintry weather on Monday or Tuesday.

Keep an eye on forecasts over the next 24 to 36 hours, as any small changes in the track of this system will dramatically change who sees snow, ice, or rain. Forecasting outlets update their forecasts every couple of hours as more model runs become available. I will make every effort to update this post through the night as new models and new forecasts roll out.

[Images: AP (from a wiped-clean grocery store in Atlanta back in January 2011), Tropical Tidbits, NWS, TWC, NWS, TWC]

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