Winter Weather Ending Tonight.


Saturday, December 21st 2013, 4:19 pm
By: News On 6


So far this freezing rain event has largely been an issue for the elevated surfaces such as trees, power lines, and to a certain extent bridges and overpasses. Most of the roads themselves have just been wet so far and the soil temperature map on the right, courtesy of the OK Mesonet, is one reason why. As you can see, soil temperatures are well above freezing but keep in mind that is at the 2" level under sod. With air temperatures hanging around the freezing mark, elevated surfaces including everything from the grass on the ground to trees to power lines are cold enough that much of the liquid rain that falls will freeze on contact. Thus, the freezing rain that is accumulating on elevated surfaces.

Also, since temperatures have been below freezing for many locations, that makes it difficult to determine just how much precipitation has fallen. The second map on the right, also courtesy of the OK Mesonet, shows the 24 hour precipitation totals. As you can see, locally heavy rains have fallen over the more SE counties where temperatures stayed above freezing, but along and NW of I-44 there are fewer rain gauge reports due to the freezing temperatures. The overlay shows radar estimates which helps to fill in those missing reports.

By the way, I have mentioned this before but the reason this is falling as freezing rain is perhaps best explained by the graph on the right. It shows the vertical profile of temperature in an event such as this. As you can see, a shallow layer of sub-freezing air near the surface is overlaid with a substantial layer of warm, wet air just above the surface. Thus the rain becomes super-cooled as it falls into the shallow, cold layer and will then freeze on contact. If the sub-freezing layer were much thicker and the warm layer much thinner, then we usually wind up with sleet. And, in the event the column of air is below freezing all the way up, then we get snow.

As we go through the rest of the day today and into the night tonight, colder air aloft will be spreading across the state and the precipitation will be changing over to snow. However, there will also be a dry slot working in bringing much of the precipitation to an end and limiting the potential accumulations. The I-44 corridor will be on the fringe the way things look now with a dusting to perhaps an inch and several inches more likely further NW and into KS.

Additional travel issues due to the snow may be a concern for those locations, but quite frankly the greater concern for the overnight hours is the temperature. As mentioned earlier, so far the roads have just been wet. But as the precipitation comes to an end and temperatures drop into the mid 20s, those wet surfaces will become icy surfaces creating greater travel problems for the first hours of the morning on Sunday. The precipitation will have ended by Sunday morning, but don't look for much in the way of sunshine for at least another day or two. The cloudy skies together with northerly winds will likely keep temperatures below the freezing mark through the day Monday. Christmas Eve and Christmas Day though will see more sunshine and daytime highs at least back into the 40s.

In fact, much of the coming week looks relatively quiet. So, stay tuned and check back for updates.

Dick Faurot