Freezing rain happens when liquid raindrops fall through cold air that is below freezing and then instantly freeze on contact with surfaces like roads, trees, and power lines.

What freezing rain is

Freezing rain is plain liquid rain that becomes a coating of ice the moment it hits something that is at or below 0 °C (32 °F). Meteorologists call these drops supercooled because they are colder than freezing but still liquid while falling.

Step‑by‑step: how it forms

Think of the atmosphere as layers with different temperatures stacked above your head.

  1. Snow forms high in the cloud
    • High up, temperatures are below freezing, so precipitation starts as snowflakes or ice crystals.
  1. Snow falls into a warm layer
    • Below the cloud there is a deep layer of air that is above 0 °C.
    • In this layer, the snowflakes completely melt into regular raindrops.
  1. Raindrops pass through a shallow cold layer near the ground
    • Close to the surface, there is a thin layer of subfreezing air, but it is not deep or cold enough to refreeze the drops into sleet (ice pellets).
 * The drops cool below 0 °C without turning to ice, becoming supercooled liquid.
  1. Instant ice on impact
    • When these supercooled drops hit a surface (roads, sidewalks, branches, power lines, aircraft) that is at or below freezing, they instantly freeze into a smooth, clear layer of ice.

A simple picture:

  • Deep warm layer in the middle → melts snow to rain.
  • Shallow cold layer at ground → cools drops below freezing but does not refreeze them in the air.
  • Cold ground → snap, a glaze of ice as soon as the drops land.

Weather patterns that cause freezing rain

Freezing rain usually shows up with certain large‑scale weather setups.

Warm front and “overrunning”

  • Commonly happens ahead of a warm front when warm, moist air moves over a shallow dome of cold air at the surface.
  • The warm air aloft produces rain, but the cold air near the ground keeps surfaces below freezing, setting the stage for freezing rain.

Frontal occlusions and terrain effects

  • A cold front overtaking a warm front (occlusion) can trap cold air near the ground, especially around mountain ranges such as the Appalachians, favoring freezing rain.
  • Valleys and low‑lying areas can hold cold air while warmer air flows above, again creating the classic setup: warm above, cold below.

Pressure patterns

  • Strong pressure contrasts between nearby low‑pressure (cyclone) and high‑pressure (anticyclone) systems can increase the flow of warm, moist air over entrenched cold air, boosting the chance of freezing rain.
  • Broad, weak low‑pressure areas with fuzzy fronts (extended lows) can also support long‑lasting freezing rain when warm overrunning persists over shallow surface cold air.

Why freezing rain is different from snow and sleet

All three depend on the temperature profile with height.

  • Snow:
    • Air stays at or below freezing all the way down, so flakes never melt.
  • Sleet (ice pellets):
    • Snow melts in a warm layer aloft, then falls through a deeper, colder layer near the ground and has time to refreeze into small ice pellets before hitting the surface.
  • Freezing rain:
    • Snow melts in a warm layer, then crosses only a shallow cold layer near the ground, so drops become supercooled but do not have time to refreeze before impact.

A common informal term for this pattern is a “warm nose”: a warm layer sandwiched between two colder layers, with the lower cold layer being too thin for sleet.

Why it’s so hazardous

  • Extremely slippery surfaces: A smooth, clear glaze forms, often more dangerous than packed snow because it can be nearly invisible (“black ice”).
  • Tree and power‑line damage: Ice adds a lot of weight, breaking branches and bringing down lines, sometimes leading to major outages and classic “ice storms.”
  • Transport and aviation risk: Roads become treacherous and aircraft can collect ice rapidly when flying through freezing rain, which is a serious icing hazard.

Quick recap (TL;DR)

  • Freezing rain needs three key ingredients: snow high up, a deep warm layer that melts it to rain, and a shallow subfreezing layer near the ground over freezing surfaces.
  • The raindrops become supercooled in that shallow cold layer and freeze instantly on contact, coating everything in ice.
  • It most often occurs with warm fronts and overrunning warm air over shallow surface cold air, especially near terrain and in certain storm patterns.

Information gathered from public forums or data available on the internet and portrayed here.