We experienced a true wintry mix Sunday afternoon — sleet, freezing drizzle, even uncommon graupel (snow pellets).
A layer of mild air was sandwiched between cold air aloft, where snow was falling from the middle of the clouds, and subfreezing ground temperatures. If the warmer intervening layer is shallow, partially melted snowflakes refreeze into ice pellets. Sleet is translucent like ice, allowing light to pass through.
Graupel, or soft hail, bounces off decks and windshields and is less common. Snowflakes come in contact with supercooled (liquid) water passing through a milder layer below the cloud base. Water freezes and coats the crystal (rime). Most graupel is about 0.2 inch in diameter, but can come in larger chunks.
If the layer of above-freezing temperatures is deeper, raindrops remain unfrozen all the way to the surface, and the freeze to form a glaze. Freezing drizzle is potentially dangerous because that’s how black ice forms, which looks wet, but is deceptively slick to walk or drive on.
Hail is normally associated with a thunderstorm, composed of multiple layers surrounding a water droplet carried aloft by strong updrafts into very cold air in the upper region of the storm cloud.