A snowstorm brings out all of the usual preparations in a community accustomed to winter's white knockout. Schools are closed. Roads are cleared. Shovels come out of the closet. Markets sell out of bread and milk.
But freezing rain — the exacting intersection of precipitation and falling temperatures — is more rare. And it seems that pedestrians and drivers alike are caught off guard.
Just ask Defense Secretary Robert Gates, who broke his shoulder Tuesday night after a nasty slip on a sidewalk following ice storms in the Washington, D.C. area.
Gates was not alone. Emergency rooms in the national capital were flooded with injuries. Area roads and highways were clogged with traffic due to multiple pile-ups and countless fender-benders. The polls in Maryland's primary election were extended by an additional 90 minutes as voters struggled to get to voting booths in the icy conditions.
And with forecasts calling for continued poor weather up and down the East Coast this week, its anyone's guess where the ice storm will land next.
Dr. Robert Shesser, M.D., head of Emergency Medicine at George Washington University hospital, said his emergency room had seen "a 30 percent surge in volume over the last 24 hours."
Compared to a winter blizzard, an ice storm has "a danger that kind of sneaks up on you," says Robert Kelly, Chief of NOAA's Forecast Operations. "In anticipation of a blizzard, people tend to take mitigating actions ahead of time. With freezing rain, people don't."
Shesser said people injured by Tuesday's ice storm are still trickling into his emergency room, most with minor injuries from slips and falls.
It is the exact opposite phenomenon that he sees in the emergency room during a snowstorm. "For us, volume goes way down during a blizzard because nobody comes out."
Freezing Rain Explained
At NOAA's HydroMeteorological Prediction Center, Kelly describes freezing rain as "highly treacherous," explaining that, as a driver, at first glance "you can't necessarily see the ice and it might look like things are just wet, when they're icy."
What does it take to get freezing rain conditions? Kelly explains that rain needs to fall in liquid form — not cold enough in the air for snow or sleet to form — but land on surfaces where the ground temperature is at most 28 degrees.
Everything, he says, "tree branches, wires, overpasses — all those things exposed to the [28 degree] air — can be below freezing. So when the rain lands on them, the water simply freezes to ice."
Compared to sleet, which freezes while falling and appears as a coarse, crystalline frost coating the ground, freezing rain appears as a wet, clear glaze. Kelly says that makes freezing rain "more dangerous because you can't see it, you can't even tell by looking when the rain freezes on the street … you put on your brakes not realizing that there's ice on the road."
The Weight of Frozen Water
Ice can also build up quickly on tree branches and electrical wires, where the weight of the frozen water can create severe power outages and contribute to hazardous driving conditions.
Buzz Bernard, a meteorologist at the The Weather Channel, says that with more than a quarter-inch of ice creation, tree limbs can get heavy and take out power lines. Downed wires lead to power outages like the ones that have swept the Northeast this week.
"The heavier the rain, the faster the ice is going to build up," Bernard says.
Adequate drainage is another problem adding to the already dangerous situation caused by freezing rain, he explains.
"A lot of areas got snow, then they got sleet, then they got ice, then they go plain rain, and, by that time, the storm drains are so clogged up the water has no place to go. Unless you can clear the storm drains once the colder air pushes in behind the rainfall, it's going to refreeze," Bernard says. "You've got a small window."
AAA released winter driving tips offering guidelines on vehicle preparation, trip planning and careful driving.
The AAA and meteorologist Kelly both agree that winter driving and a full gas tank go hand-in-hand.
"People's perception of dangerous winter weather is a blizzard," says Kelly, "But an ice storm is deceptively dangerous because you lose power … roads freeze, you get into accidents, people slip and fall down."
"The freezing rain scenario can come quickly," he warns drivers, advising that they wait until the roads are salted because salt water has a lower freezing point. "If the temperature is near 32 and it might rain, there could be a problem."
ABC News Lauren Effron contributed to this report.