January 25, 2008 at 4:16 am | Posted in Uncategorized | Leave a comment

Light rain began to fall across north Texas during the evening hours on Thursday. And in some areas, that rain was mixed with sleet (ice pellets). But temperatures were above freezing. So how does that happen?

In this case those initial raindrops were falling into a dry air mass near the surface. As they fell, the rain drops began to evaporate. But evaporation is a cooling process. (Remember how perspiration helps cool you down in the summer?) And the evaporation cooled those rain drops to the freezing point, so that some of them froze into tiny ice pellets, or sleet. But once they landed, they quickly melted.

The real concern will be early Friday morning. By then, enough rain will have fallen to drop our temperatures below freezing. And once that happens, the rain will change over to freezing rain, which may begin to coat some local bridges and overpasses with a thin glaze of ice. I don’t expect any big accumulations, but just a little ice can cause havoc with the morning rush hour. A Freezing Rain Advisory is therefore in effect for the Metroplex.

But north and west of Fort Worth, the temperature will be below freezing for a longer period, so ice accumulations will be greater. In those areas, up to 1/4 inch of ice may be possible on bridges, overpasses, and even some road surfaces. There, a Winter Storm Warning is in effect.

But by Friday afternoon, the entire area will be back above freezing, and any ice will be only a memory. We will enjoy a real nice warm-up over the weekend, back into the 50’s and 60’s.

Chief Meteorologist David Finfrock


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