This weekend will be active as a strong storm system transects the state. Let me start off by saying any sort of winter weather mischief will likely be confined to the Texas Panhandle, northern sections of the South Plains and Rolling Plains, and perhaps a sliver of Northwest Texas. The remainder of Texas will be too warm for any winter weather precipitation or impacts. However, we’ll be dealing with separate impacts where temperatures are above freezing. The upper level storm system responsible for our weekend weather is just now approaching the west coast of the United States. Once it gets onshore and in our upper air observation network we’ll be able to hone in on a particular forecast scenerio with confidence. Until that happens we’ll be dealing with some inherent uncertainty such as the storm system’s track, the exact location of the freezing line, where the heaviest precipitation totals will set up, and how much instability will be available on Sunday for thunderstorms in Central Texas.
Let’s start out with the time-frame for precipitation. While these chances are certainly subject to revision the best chance of precipitation seems to be Friday through Monday, generally from west to east. It won’t rain all the time where the highest rain chances are located, but a fairly wet period is expected. Once we get closer in time and more accurate forecast data we should be able to provide more detailed timing on each wave of precipitation.
The highest precipitation totals are expected to be in the eastern Texas Panhandle east along the Red River into North Texas and Texoma. At this time widespread rainfall or liquid equivalent totals of two to four inches are expected in that zone. We could see widespread one to three inch rains south into the Big Country, Concho Valley, Hill Country, Central Texas, into Northeast Texas. These totals will undoubtedly shift as confidence increases on the track of our incoming storm system. Take these as a generalized amounts over a region with the expectation that the highest rain totals will shift. Locally higher amounts are possible while some folks will see much less over a smaller area than these rain maps indicate. Localized flooding will be possible with a higher risk of river flooding next week.
The position of the freezing line will be critical in determining who ends up with a cold rain at 33 degrees or a winter weather event at 31 degrees. At 32 degrees we may start to see icing on elevated objects like tree branches and power lines. At 31 degrees we start to see more bridges and elevated surface ice over. Finally, at 30 degrees or below we freezing rain will generally accumulate on all objects, including surface objects (roads). A few other factors go into how ice accretion such as how warm a water droplet is and will it instantly freeze on contact. Of-course forecasting precipitation types can be challenging as well.
There is the potential for freezing rain in the Texas Panhandle by Friday morning into Friday night as temperatures remain below freezing. The reason we’re forecasting a freezing rain event at this juncture is due to a layer of warm air a few thousand feet above the ground. Snow falls into that layer of warm air and melts into rain. Those water droplets fall back into the freezing airmass near the surface and become super-cooled. If the layer of sub-freezing air is thick enough between the surface and the layer of warm air then the water droplets can freeze back into ice pellets (sleet). If the whole atmospheric column is below freezing than the precipitation type is snow. With a layer of warm air expected on Friday and Saturday the chance of snow will be low. By Sunday we may see a change-over to snow in parts of the Panhandle as colder air filters in. All of this is low confidence and could easily change depending on the storm system’s track, the behavior of the cold front and freezing air mass, and overall precipitation chances. There is the potential for accumulating ice on Friday with some indications that temperatures will warm above freezing on Saturday in the Texas Panhandle. By Sunday we may see temperatures go back below freezing with a change-over to snow. Depending on the storm system’s track some of that snow could bring significant accumulations. Winter weather forecasting in Texas is difficult at the best of times – and this situation is far from ideal. Stay tuned for forecast updates on the winter-weather aspect of this system.
Meanwhile, we continue to monitor for a low risk of severe storms on Sunday. At this juncture the atmosphere is not forecast to become more than modestly unstable. Wind fields will be quite strong across Central Texas on Sunday, but a fairly stable air mass would prevent more than an isolated severe storm risk. If the projected instablity values increase so would the risk of severe storms. Keep an eye on the updated forecasts as we head into the weekend.