Saturday, February 01, 2014

More ICE Than Snow for Some?

New data is coming in and it looks a little more ICY on Sunday (tomorrow). As you recall from the earlier blog, sleet can drastically lower "accumulation" totals because it does not "accumulate" as fast as the puffy snowflakes. Sleet, snow, and freezing rain all accumulates differently. Because of that, let's just talk about the "liquid equivalent" for a moment. That means, let's pretend we melt all of it to liquid and show how much will fall and where. Here's the liquid equivalent of the sleet in orange, freezing rain in pink, snow in blue. The green precipitation map just shows the rain equivalent. Notice how much sleet and freezing rain (glaze) is projected to fall according to this model instead of snow. Click to enlarge:
So, what does that do to our forecast? Here are some thoughts Andrew and I are bouncing around:
  • First, both the GFS and NAM are leaning towards the icier setup, BUT snow will still fall on top of the icing. Some places more than others.
  • Second, we do plan to nudge the snow accumulations farther NW and increase the ice threat.
  • Lastly, we are going to start becoming more concerned with power lines and trees. This is NOT a 2009 situation, but we could see some icing similar to what we saw at the start of last December, which caused a few power issues.
So, what changed? Well, the models are hinting at a layer of warmer air from 3800' to 9800'. In that column of 6,000 ft, the snowflakes would MELT into raindrops. As they continue falling from 3800' to the ground, they will either refreeze into sleet OR fall as liquid and freeze on contact to a glaze. Here's a Skew T for Sunday afternoon using the NAM model. Imagine this a vertical representation of the atmosphere. Snowflakes form high in the sky, melt coming down, and then cause icy conditions at the surface:

If that layer of warm air does not materialize, we will stay mostly snow and see more accumulation. That's why we have a "range" for the uncertainty. The best chance for all snow is NW of Jonesboro. Places like Sharp County may see all snow.

Andrew will have an updated accumulation map at 6:00 and 10:00 on Region 8 News!

Stay tuned!

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