LITTLE ROCK, Ark.- From Monday, November 30, through Friday, December 4, is Winter Weather Awareness week here in Arkansas.
This is a good time to go over some different aspects of the winter months ranging from winter precipitation types, the difference between winter weather watches, advisories, and warnings as well as some winter safety tips.
We are all familiar with rainfall but on the seldom occasions, it seems like we can also observe winter precip types like freezing rain, sleet, and snow.
For us to receive snowfall, nearly the entire column of air from the cloud base where the precip is occurring to the surface must be less than 32 degrees Fahrenheit. While it is possible and we have even observed this, snowfall can reach the surface while the air temperature is slightly above freezing. The reason why is because that layer of air that is above freezing at the surface is very thin (likely <100ft). If it were to become thicker, our precip type may no longer be snow.
Sleet occurs when the precip begins as snow in the cloud but then falls through a shallow layer of air that is above freezing. It partially melts before descending back into below-freezing temperatures. It will refreeze and form the sleet that is observed at the surface.
Freezing rain happens when the precip either starts off as rain or snow but melts before reaching the surface. At the surface, there is a shallow layer of air that is below freezing. This causes liquid precip to begin to freeze on contact with objects at the surface resulting in freezing rain.
WATCH, ADVISORIES & WARNINGS:
During the winter months, even sometimes, late fall and early spring, certain watches, advisories, and warnings will be issued to highlight certain winter weather events and their importance.
Winter Storm Watch– Issued when there is the possibility of the following weather scenarios either separately or in combination:
- Snow accumulations of 4 inches or more. Lesser amounts like 2 to 4 inches can be used if the forecaster at the National Weather Service Office feels there could be significant impacts.
- Freezing rain or freezing drizzle accumulations of 1/4″ or more.
- Sleet accumulations of 1/2″ or more.
Winter Weather Advisory– Issued when the following conditions are expected separately or in combination:
- Snow accumulations of 1 to 3 inches. An advisory can be issued for 1 inch or less depending on the situation where extra caution is warranted by the National Weather Service forecaster.
- Sleet Accumulations of less than 1/2″
- Freezing rain or freezing drizzle accumulations of less than 1/4″
Winter Storm Warning (NEW Criteria)– This year, the warning criteria changed for the Little Rock office to help create a more cohesive relationship with surrounding offices with their winter storm warning definition. A warning will be issued when there is hazardous weather occurring, imminent, or has a high likelihood of happening below separately or in combination:
- Snow accumulations of 4″ or more. Lesser amounts of 2 to 4 inches can be used if the National Weather Service forecaster feels the impacts could be significant.
- Sleet accumulations of 1/2″ or more.
- Freezing rain or freezing drizzle accumulations of 1/4″ or more. (If this is not expected in combination with the other types, then an ice storm warning will likely be issued)
Ice Storm Warning– Issued when significant or possibly damaging accumulations of freezing rain and/or freezing drizzle are expected.
- Ice accumulation of 1/4″ or more.
Wind Chill Advisory– Issued when wind chill values will reach 0 degrees Fahrenheit to 15 below zero Fahrenheit with average wind speeds around 10 mph or stronger with conditions lasting for 3 hours or longer.
Speaking of wind chill, why is it important to know this value? Wouldn’t the air temperature suffice? Not exactly. As noted in the graphic below, when there is no wind, a thin warm layer exists around our body. When there is wind, it will break up that fragile warm layer and cause heat to be moved away from our body. In doing so, our body will attempt to compensate for heat loss and causes our body temperature to drop.
Wind Chill Equation:
Twc= 35.74 + 0.6215T – 35.75(V0.16) + 0.4275T(V0.16)
V = Wind Speed in mph
T = Air Temperature inoF
Knowing the wind chill which factors wind and air temperature will help you understand the amount of time it would take for frostbite to occur. While in most cases it will take a long period of time in Arkansas for this to occur, it is something to watch when we have frigid/windy nights.
WINTER & TRAVEL:
During this winter season, it is also very important to keep watch on travel conditions across the state when snow, freezing rain, sleet is forecast.
While traveling is highly discouraged during times of winter weather, it is understandable that some may not have this option.
To monitor road conditions, the Arkansas Department of Transportation has a website where you can track road conditions during the times mentioned above. You can find it HERE.
THE 4 Ps:
During this winter season, always remember the 4 Ps-
People- Check on those who have difficulties handling cold temperatures.
Pets- Make sure outdoor animals have sufficient shelter, food and water. Make sure the water has a way of not freezing.
Pipes- Cold weather cause wreak havoc on pipes that are not properly insulated.
Plants- Take care of any plants that cannot handle freezing temperatures