A polar cold front moving through the region on Thursday resulted in increased moisture and cooler air across Central Texas early Friday morning. Numerous reports of sleet (also known as ice pellets) and graupel (tiny frozen-over snow pellets) were reported through Hill Country and the San Antonio/Austin metro area. Sleet was also observed in Del Rio and at Laughlin AFB.
Small hail (about pea-sized) was also reported in Del Rio briefly around 8 AM.
Small hail, graupel, and sleet, while similar in appearance, differ in the processes by which they are made. Hail is formed due to convective processes that cause a rain drop to be lifted back to a point where it freezes before falling again - often several times. While often found in thunderstorms, hail can occur without thunder and lightning. Hail is often quite durable. Graupel is formed by supercooled water droplets which form over a snowflake and is often very brittle to touch, routinely taking the appearance of Styrofoam particles (opaque white). Sleet (ice pellets) is (are) formed when a falling water droplet re-freezes in a cold layer before falling to the ground. Sleet is often very small and clear.
All of these types of precipitation may fall a surface temperatures above freezing. Often, however, sleet and graupel will fall when the freezing level (altitude where the air reaches 32°F/0°C) is relatively low to the ground. Hail may fall with high freezing levels as it is often convectively forced.
For more information, contact Smalltown Weather at SmalltownWeather@gmail.com or (830) 313-6899