Joel's Blog: Mississippians see a mixed bag of weather - WLOX.com - The News for South Mississippi

Joel's Blog: Mississippians see a mixed bag of weather

Four inches of snow had accumulated in Tallahatchie County by mid-afternoon. At least six inches had been reported by sunset. Four inches of snow had accumulated in Tallahatchie County by mid-afternoon. At least six inches had been reported by sunset.
A snowflake that doesn't melt completely will refreeze before reaching the ground. This is a sleet pellet. A snowflake that doesn't melt completely will refreeze before reaching the ground. This is a sleet pellet.
A snowflake that melts completely will not refreeze before reaching the ground, but will freeze on contact. Freezing rain leads to major issues with black ice. A snowflake that melts completely will not refreeze before reaching the ground, but will freeze on contact. Freezing rain leads to major issues with black ice.

While much of South Mississippi has experienced cold, soggy conditions this Wednesday, the well-advertised winter storm for Central and North Mississippi has been underway for several hours.

Light showers began to make their way into the state early Wednesday morning, shortly before sunrise. At the time, most of the precipitation fell as rain or freezing rain. Throughout the morning and early afternoon, each raindrop, sleet pellet or snowflake contributed to a process called dynamic cooling—promoting a more favorable environment for heavy snowfall later in the day.

Of course, it's a beautiful sight for most of us in the South who rarely see snow. But as we learned in January of 2014, travel becomes a major hazard, especially on bridges and overpasses.

Winter weather is certainly one of the most challenging types of weather to forecast, especially in the south. During the summer, it's easy to determine precipitation types. In the winter, a thin layer of air where temperatures are above or below freezing may mean the difference between rain, sleet, freezing rain or snow.

So what's the difference? We're all very familiar with rain, but people often get confused when it comes to this mixed bag of precipitation we get on occasion here in the Deep South.

When precipitation develops in the upper-atmosphere this time of year, it usually begins as a snowflake. Yes, even the rain we see here on the coast sometimes begins as snowfall (way above the surface), then melts on the way down. Here's a detailed look at what other precipitation types we've seen in Mississippi today.

Snow is pretty simple. When an entire column of the atmosphere is below 32 degrees, melting will not occur. As long as the surface is below freezing, this snowfall will accumulate.

Sleet is not quite as simple, though. It begins as a snowflake, but when it passes through a thin layer of temperatures above 32 degrees, part of the snowflake melts. If the layer is thin enough, it may fall through another layer of freezing temperatures. As long as the flake has not completely melted, the liquid coating on the outside of the snowflake will refreeze, creating a sleet pellet that often bounces once it hits the ground.

Freezing rain is similar, but occurs when the melting layer is much thicker and the snowflake melts completely. This becomes a pure raindrop and will not refreeze while falling because it needs something to freeze to. With sleet, part of the snowflake is still frozen; but liquid water must have something to cling to in order to freeze. When it reaches the surface, where temperatures are freezing or below, the rain freezes on contact. This creates a much greater hazard to motorists than anything else because it creates a glaze on the roadways known as black ice. It is also the most damaging to trees and power lines because of the weight of the ice.

Another type of precipitation that we DID NOT see Wednesday in Mississippi is hail. Many people confuse this with sleet because both fall as pellets or chunks of ice. They may be similar in ways, but the process that creates the precipitation types is completely different. As mentioned earlier, sleet begins as a snowflake. Hail occurs in a much warmer atmosphere and begins as a raindrop. As it falls, it encounters a rush of air called an updraft, suspending the raindrops into the air with small particles of dust or even bugs into the top of the thunderstorm. The raindrop will freeze onto these small particles once it reaches the top of the storm, growing in size until it becomes too heavy for the updraft to suspend it into the freezing layer. These chunks of ice are much larger than sleet pellets and cause major damage when they come crashing to the ground.

Temperatures here in South Mississippi are a bit too warm to support anything besides rainfall. However, as the rain exits the region Wednesday night, temperatures may approach freezing inland before all the water has cleared the roadways. Because of this, use extra caution in these areas as there may be pockets of black ice early Thursday morning.

As always, be sure to turn to WLOX and WLOX.com for more detailed information concerning our forecast here in South Mississippi. For more information concerning travel conditions in Central and North Mississippi, you can find streaming video of MDOT Traffic Cams on their website: www.mstraffic.com

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