12:15 AM CST | December 13, 2018
I just wanted to do a quick update on the trends this evening. First off, a few models have come in slightly warmer and slower with this system. What does this mean? It means that, while snow is still likely for western North Texas, it may be more localized. As mentioned over the last several days, the snow potential depends heavily on the cold temperatures aloft. Heavy precipitation rates will help transport this colder air to the surface, allowing for a switchover from rain, to rain/snow, to snow in some places. It will be a situation where, a friend 10-15 miles to the west may get 3 or 4 inches of snow, but you see none. That is what is challenging to forecasters right now. Where these areas of snow set up, there will be travel impacts given the strong winds.
As for the severe potential, I still see the potential for a couple low-topped supercells for parts of North/Northeast Texas during the afternoon hours. If the system is a few hours slower, this risk could extend as far west as I-35. For more information on cold core setups, there is an excellent case study by Jonathan Davies available here. He has done multiple research papers on these types of setups across the Central Plains. While not as frequent, Texas does see these setups from time to time. In short, the proximity of the upper-level low (and its cold temperatures aloft) to the surface low can compensate for a lack of greater moisture and instability. Sunshine may be what makes or breaks this potential tomorrow. Lapse rates are the temperature change with height. If breaks in the clouds allow for surface heating, the greater the temperature change and the "steeper" the lapse rates. The steeper the lapse rates, the more unstable we will become. If these conditions materialize, the most likely time for a few severe storms will be between 3:00 and 7:00 PM. Large Hail will be the primary hazard, followed by a brief Tornado. Do I expect "widespread" severe weather? No. Why am I mentioning this? Because while snow has been the bigger story with the media, there will be a conditional risk for severe weather that should not be overlooked.