Ice storm warning
An Ice Storm Warning is issued by the National Weather Service when freezing rain is expected to produce ice accumulation of at least 1/4 inch, and some offices set that line at 1/2 inch. Freezing rain falls as liquid and freezes on contact with surfaces at or below 32 degrees Fahrenheit, forming a glaze. At that thickness, tree limbs and power lines begin to fail and roads can become impassable.
Right now0Ice storm warnings in effectas of Snow totals by state, measured
Freezing rain, sleet and snow
| Type | What it is | What it does on the ground | Which alert covers it |
|---|---|---|---|
| Freezing rain | Rain that freezes on contact with surfaces at or below 32°F | Forms a coating of ice on trees, roads and power lines | Ice Storm Warning for 1/4 inch or more; Winter Weather Advisory for thinner amounts |
| Sleet | Ice pellets form when rain freezes before it hits the ground. | Bounces on impact and does not glaze surfaces | Winter Weather Advisory for lighter amounts; Winter Storm Warning for heavy accumulations |
| Snow | Ice crystals that fall and accumulate | Accumulates, drifts and makes roads and walkways slippery | Winter Storm Warning for heavy snow; Winter Weather Advisory for lesser amounts |
Why a quarter inch is the line
A quarter inch of glaze is enough to add hundreds of pounds of weight to a span of power line, and at that thickness tree limbs start to break. At half an inch, widespread outages and restorations that take days are typical, according to the National Weather Service.
Staying safe when an ice storm warning is in effect
- Stay off roads, especially bridges and overpasses, which freeze first.
- Power outages are possible, so charge devices and keep flashlights ready.
- Never run a generator or grill indoors.
- Stay clear of downed power lines.
- Keep away from trees that are heavy with ice.