AUSTIN (KXAN) — While it might feel cold enough for snow outside, several factors mean that our precipitation type this week will be rain and freezing rain, rather than snow.
It all has to do with the temperature profile of the atmosphere. Temperatures Wednesday morning were frigid, with some areas dropping into the 20s.
Temperatures overnight into Thursday morning will get even colder with lows in the metro even expected to fall below freezing.
Rain transitioning into freezing rain and freezing drizzle is expected to occur tonight through tomorrow morning.
Some models are projecting to have up to a tenth of an inch or even more of ice in the Hill Country.
With that said, why is ice/freezing rain in the forecast and not sleet or snow? It has to do with the temperatures high up in the sky.
For snow to fall, you would need all layers of the atmosphere to be at or below freezing. For at least sleet to fall, you would need a much thicker layer of below freezing temperatures than what we currently expect. The surface layer of below freezing temperatures we currently have is very shallow (meaning only a few thousand feet thick!).
Below is a sounding (temperature profile) of the atmosphere. It shows that just about 3000 feet up in the sky the temperature warms up to nearly 55°F. Because of this, liquid rain or drizzle will fall from the sky and then freeze on contact with the freezing cold ground making for “freezing rain.”
Let’s talk about accumulation. Will this be a widespread, impactful icing event?
One of the reasons for that is because of the extremely warm temperatures we experienced Tuesday. We reached 88°F at Camp Mabry. The ground, including all the surface roadways, is still holding on to a lot of that heat from Tuesday. It will take several hours to days for those roads to cool down enough to be problematic. In other words, it will be tough for the ice to stick and not melt on the ground.
The Texas Water Development Board has a great interactive mapping tool with rain gauges and soil temperatures for Central Texas.
As of late Wednesday morning, its maps show area-wide 50°F and 40°F temperatures at ground level. That’s too warm for freezing rain to initially stick. With that said, another 12- to 24-hours or so of below freezing or near-freezing surface temperatures will be enough for the ground to cool and be cold enough for some light icing to accumulate and be problematic, especially on elevated roadways, surfaces and bridges. This will especially affect areas out in the Hill Country that are significantly colder and colder for a longer period of time.