The National Weather Service has issued a Winter Weather Advisory for Central Texas until 6 p.m. tonight. Forecasters warn a wintry mix of precipitation could make for treacherous road conditions. Much of that precipitation will be your run-of-the-mill rain and sleet. Some of it will be graupel (pronounced "grau-puhl").
Right about now, you're probably wondering what exactly graupel is.
Think of frozen precipitation as a spectrum. If snow's on one end, and hail's on the other end, sleet – and graupel – exist right there between the two. While snow is crystalized precipitation and hail is frozen raindrops, graupel is sort of a combination of the two.
It's formed when there are above-freezing temperatures on the ground and very cold temperatures in the air. So, a snowflake forms, then it's caked with near-freezing drops of rain, forming something akin to Dippin' Dots ice cream, as the National Weather Service notes.
Sleet, on the other hand, is formed when there are near- or below-freezing temperatures on the ground and warmer temperatures in the air. That combination melts snow crystals and they refreeze as they drop to the ground.
Compared to its more famous sister, sleet, graupel is an opaque white, while sleet is made up of translucent ice pellets that never fully crystalize on their way down.
The National Weather Service in Austin and San Antonio tweeted photos Friday morning showing graupel and sleet falling at the same time in South Austin's Circle C subdivision.
7:55a - Want to dive in a bit more to the differences between sleet and graupel. Here is a graphic from @NWSChicago they produced last year detailing some of the differences. pic.twitter.com/Jgxhu6g24G— NWS Austin/San Antonio (@NWSSanAntonio) February 8, 2019
This is an EXCELLENT picture of the difference between sleet and graupel. The sleet are the clear bits of ice, while the graupel are the cloudy snow grains. We are seeing both across the area this morning. Thanks for continuing to share your reports! https://t.co/qM5MVrrjbg— NWS Austin/San Antonio (@NWSSanAntonio) February 8, 2019
The National Weather Service expects temperatures to warm above freezing by the late morning hours, with today's high expected to be near 39 degrees. (Compared to Thursday's high temperature of 72 degrees.)