Fall severe weather season underway

Published 7:00 am Tuesday, November 10, 2015

This week’s weather looks quiet, with the possible exception of Wednesday night when an approaching cold front associated with a strong low passing to our north will give us a chance of thunderstorms.
Most people think of springtime as the season for tornadoes and severe thunderstorms, and rightfully so. But in our area, there is a secondary peak in severe weather. Climatologists have named a broad area of Mississippi, Louisiana, Alabama, Tennessee, and Arkansas as the “Dixie Alley” of tornadoes. A number of significant tornadoes have occurred over the years in Dixie Alley in the months of November and December.
Over the past 35 years, four tornadoes have struck Pearl River County and northern Hancock County in November and December. The most severe was the Christmas Day tornado in 2012.
Two of the key ingredients usually needed for severe thunderstorms and tornadoes are wind shear and instability.
In fall and early winter, the polar jet stream in the upper atmosphere is becoming stronger and pushing further south. This can mean sharp differences in wind speed and direction at various heights in the atmosphere, which can provide the twist needed to initiate tornadoes.
The more rapidly that temperature decreases with height, the more unstable the atmosphere is. Here in Dixie Alley, in the late fall and early winter we sometimes still have enough relatively warm air near the surface to create instability.
Wednesday and Wednesday night an especially strong wave in the jet stream will be moving through Arkansas and Missouri. Instability will not be all that great with this system, but there will be a lot of energy associated with the upper level winds, and the National Weather Service is expecting severe thunderstorms and some tornadoes to develop from northern Mississippi northward.
Here in Pearl River County we have about a 50/50 chance of thunderstorms Wednesday night, but the strongest chance of severe weather should stay to our north.
Still, it’s a good time to make sure you and your family are ready in case we have severe weather from this system or another during the November-December severe weather season.
First, make sure you have a way of receiving tornado and severe thunderstorm warnings when they are issued. A warning means that severe weather has been detected, is about to hit, and you should take action immediately. (A watch just means that conditions are favorable for severe weather, and that you should keep up on the weather.) A number of phone apps are available that will alert you if the National Weather Service issues a warning.
A weather radio is another good alternative.
Second, have a plan for you and your family. Where will you take shelter if a warning is issued? If you live in a sturdy house, an interior bathroom or closet is often the best bet. If you live in a mobile home, do you have a plan to get to a sturdier structure? Consider going from the mobile home to that safe house when severe weather is expected, even before a warning is issued.

By Skip Rigney

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