Ice storms: Inside wintertime's dreaded, frozen mess
An examination of these hazards and some of Washington’s historically worst events
'There may be snow lovers galore, but no one ever roots for an ice storm.
No discussion of Washington’s winter weather would be complete without a closer look at the perils of frozen water, in the form of sleet and freezing rain. The icy sheen on sidewalks and driveways makes the mere act of walking extremely hazardous. On roads, black ice can be an outright life-threatening scenario. And we all know what happens when myriad tons of ice bow down tree limbs onto the power lines that thread through them.
In short, there is nothing ever nice about the ice.
First, a critical distinction: Sleet is the term describing those tiny ice grains that ping on our window panes and accumulate as an opaque, crunchy layer on the ground. Freezing rain describes liquid water drops that fall to frozen ground, then freeze into a clear coating on impact.
Freezing rain will glaze and completely envelop tree branches, causing them to sag as clear cylinders of ice; whereas sleet tends to just bounce off. On the ground, both forms of ice create a slick rink. But the glasslike coating of freezing rain wins when it comes to sending pedestrians wheeling, and cars sliding sideways down the slightest grade.
Sleet and freezing rain develop as a result of a layering of different air masses in the vertical, between the cloud base and ground. These layers take on a triangular wedge shape, as shown in the figure below, with warm air riding up and over a ramp of subfreezing air trapped against the surface. The Appalachian Mountains often trap the dense, icy air layer, known as a cold air dam, while Atlantic winds usher in a milder air mass that glides up and over the top.'>>>
https://www.washingtonpost.com/weather/2020/12/02/washington-dc-worst-ice-storms/?