Weekend’s tornadoes rare for January

Published 7:00 am Tuesday, January 24, 2017

Saturday morning’s deadly and destructive tornado in Hattiesburg was just one salvo in a weekend of violent and severe thunderstorms that brought hail and tornadoes across the Southeastern United States.

By the time the last severe storms moved off the Southeast coast Sunday night, the National Weather Service’s Storm Prediction Center’s preliminary report states 53 tornadoes crossed Louisiana, Mississippi, Alabama, Florida, and Georgia since Thursday.

If this number is confirmed, it would make this one of the top three January tornado outbreaks since accurate tornado recordkeeping began in 1950.

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The Associated Press reported four deaths from the Hattiesburg twister, and storms in Georgia were even more deadly with 15 deaths reported in that state on Sunday.

In addition to the tornadoes, hundreds of thunderstorms reached severe levels during the outbreak. SPC received 313 reports of high winds and 81 reports of large hail.

The volatile weather pattern that spawned the storms was more typical of springtime than of mid-winter. Unusually warm, moist air near the surface covered the southeastern United States at the same time that colder than average air at middle levels of the atmosphere moved in from the west. This resulted in an unusually unstable atmosphere for January.

All that was needed was a trigger to get air in the lower levels rising. That trigger was provided by an intense low-pressure system moving eastward from Texas toward Mississippi, sucking in more warm air from the Gulf and lifting the atmosphere over the Southeast.

Those factors were enough to produce severe thunderstorms with high winds and hail. The additional ingredient needed to generate strong tornadoes was strong winds that changed direction rapidly from the surface upward through the atmosphere.

That wind shear was present in many areas across the Southeast on Saturday and Sunday resulting in an outbreak of intense, rotating thunderstorms called supercells.

One such supercell embedded in a larger cluster of storms produced the tornado that tore through Hattiesburg and Petal on Saturday.

Not only was it unusual to have all of these ingredients come together in mid-January. It was also unusual to have the situation extend so far southward. On Sunday as the system moved over northern Florida and south Georgia, the SPC issued a rare “Particularly Dangerous Situation” Tornado Watch for that region to indicate the seriousness of the threat. Later that day tornadoes in the PDS Watch Area resulted in the deaths in Georgia.

In 2006 two meteorologists, Andrew Dean of the University of Oklahoma and Joseph Schaefer of SPC, calculated that in the decade preceding their study, in over 3,000 tornado watches issued by SPC, only 7 percent were issued as “Particularly Dangerous Situations.”

The weather in south Mississippi will be much quieter this week. An approaching cold front may kick off some showers on Wednesday before winter returns with near normal temperatures and dry air for Thursday through Monday.

During that period, forecasters predict skies to be fair with highs around 60 and lows in the middle to upper 30s.

By Skip Rigney