A comet tonight and your Sunday Story

As promised, I have included your Sunday Story below. It concerns the forecasting of wintry weather and the challenges that come with that.

But first, the NWS Nashville reminded us this morning that there is a comet tonight! I’ll be out looking for it and I’ll send out a blog update if I see anything. The NWS had this to say:

“Comet 46P or Wirtanen will pass its closest to earth today,
roughly 7.4 million miles. Theoretically visible to the naked eye, it is not easily seen without the use of telescopes or binoculars since its faint light is reflected over a very large area. You will need to find yourself a dark spot if you want to see it well. Good news is we are expecting minimal cloud cover tonight for such a viewing. For us here in Middle TN, it will be visible in the evening sky, around 530pm just above our eastern horizon. It will then reach its peak point around 10pm high in the sky looking toward the south. It will continue to be observable until around 330am before it disappears below our western horizon. If you plan on taking a gander and you spot it, let us know what you thought. Good Luck!”

Forecasting Wintry Weather

Forecasting winter weather for the plateau is never easy. We get enough cold air for snow, while being located close to the Gulf of Mexico, a major source of moisture for our region.

The problem is getting the cold air to align just right with the moisture.

To make matters worse, we have to consider the complicated terrain of the Cumberland Plateau and the impact that has on our weather. It can all cause a real headache for us forecasters!

The most complicated forecasts are those in which we find ourselves right on the border between wintry weather and plain rain. That seems to happen a lot to us here on the plateau. The difference between a cold rain at 33 degrees and an ice storm at 32 degrees is about as different as light is from dark.

Those temperatures here at the surface aren’t all that matter, either. The atmosphere is in layers from the ground up. Each layer has an effect on the type and amount of precipitation that ultimately falls to the ground. The atmosphere is like a layered cake, with each layer playing a vital role in the kind of weather we get here at the surface.

This is how we can get snow with temperatures above freezing here at the surface. That just means that the surface air that is above freezing isn’t deep enough to melt the snowflake before it hits the ground. The layer closest to the surface is too warm for snow, but one of the layers above is cold enough to keep that flake frozen for it to make it to the ground.

This winter will surely provide plenty of winter weather forecast headaches for meteorologists. Just always prepare for the worst, while hoping for the best.  


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