Friday, February 4, 2011

Why the Ice and Not the Snow?

The winter storm that moved through East Texas over the past 24 hours, produced snow, sleet, and freezing rain. This mixed bag gave us a wide variety of snow and sleet totals across the area.

Unfortunately, those of us that wanted snow, received some freezing drizzle and ice instead.

The graphic above shows that the heaviest snowfall occured in northern portions of East Texas, ranging from Palestine to Jacksonville and over to Longview.

For most of us in Deep East Texas, it was a mix of sleet and freezing rain that fell throughout the night and early this morning.

Some people have asked me why we did not see more snow as was forecasted over the past few days.

The answer lies in the temperature profile of the atmosphere. You heard me talk about the difference between freezing rain, sleet, or snow all has to do with how the temperature changes as you go up to 15,000-20,000 feet in the atmosphere.

Anytime the temperature profile is all below freezing (32°), we will get an all snow event.

However, when we see temperatures aloft above freezing, that is when it gets tricky. The diagram illustrates what happened to our temperature profile over East Texas last night.

At about 10,000 feet or so, there was a warm nose that existed. That pocket of warm air melts snowflakes as they fall through the atmosphere. If it is deep enough, the snowflake will melt into a liquid water droplet, also known as rain. If the warm is in not very deep, then sometimes the snowflake will just change to a graupel or sleet pellet.

In our case, that warm layer was present, leading to a mixture of sleet and freezing rain, with very little snow.

Our friends and neighbors to our north had sub-freezing temperatures throughout the entire depth of the atmosphere, and ultimately, another 5-7" of snow.